# Power Meter Recommendations?



## waltaz (Oct 14, 2004)

I started structured training with a coach at the end of last year, and have really enjoyed the structure and process. Everything has been HR based, as I had never used power. I picked up a Wahoo Kickr in August, and have started using it, and power, for my interval workouts. Wow; what a difference, and very eye-opening!

I’d like to look at adding power to one or two of my bikes (MTB’s only, as I don’t/won’t road ride), and thought I’d ask this knowledgeable and seasoned group for some recommendations. Don’t need the very best/most expensive; just want something that is accurate and reliable and easy to use, and, ideally, I can easily swap between bikes (so I don’t have to buy two).

Thanks if advance for any input!


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## Tyrone Shoelaces (Nov 6, 2006)

Did your coach recommend anything?


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## waltaz (Oct 14, 2004)

Tyrone Shoelaces said:


> Did your coach recommend anything?


Not yet; I just started mulling it over.

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## TDLover (Sep 14, 2014)

I would recommend building a powertap wheel if your two rear wheels match, that way you can simply swap the wheel between bikes. 

Powertap hubs are quite reliable in my experience, however, for mtb, power is not that useful depending of the terrain you ride. If its fairly flat and consistent then yes, but anything else is hard, in other words you will never be able to match your trainer's power and you might question yourself.


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## Lone Rager (Dec 13, 2013)

Agree PowerTap hubs (now owned by SRAM/Quarq) are really good. If you can easily swap a wheel between your bikes with respect to axle standards, whee/tire size and freehub, they're the easiest PM to switch between bikes. There are no mtb power pedals yet, though SRM just announced of SPD power pedals that will hit the market soon. Some have converted Assioma road pedals to SPD by changing out the pedal bodies. IDK how well pedal PMs will stand up to pedal strikes.

Crank types include crank arm, crank spider, and spindle types. Left-only crank arm types are probably the easiest among these to move between bikes. A really good objective review of PMs in general (though not specifically mtb centric) is:

https://www.dcrainmaker.com/product-reviews/power-meters

FWIW, I use Assioma Duo power pedals on the road bikes and the Zwatt Yding spindle based left/only PM on one of my mtbs. My smart trainer is a direct drive Cyclops Hammer (current model is now the Saris H3).

Agree that mtb power use is somewhat diff for me from road/trainer power as on the mtb the riding and power output various more and much more rapidly. That said, averages over 30 seconds and longer can be quite comparable. On the mtb, I use it mainly to go back and compare avgs (normalized power) over various segments that I ride rather than reference while riding or to do power based training riding the mtb.


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## Tristan Wolf (Oct 21, 2019)

Really don’t know what to say. They all seem to be expensive, and to truly make use of it one should have power meter that measures power on both cranks independently. And that screams EXPENSIVE!


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## Sidewalk (May 18, 2015)

I've been happy overall with the Cinch PM. I have one on a Turbine crank (I train on my Enduro), and one on my XC bike with Cannondale cranks.

I recently got a Stages crank arm on my gravel bike, but it seems to eat the battery like crazy. I am guessing it wakes up when getting jostled, so eats the battery up when it is on my bike rack and driving.


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## Poncharelli (Jan 13, 2005)

I really want to try a different PM but my Powertap hub keeps going, and going, and going.....

Same road bike powertap hub since 2008 (paid $1100 with a Mavic Open Pro). Rebuilt by Saris once ($400). 4 rims on it so far. Got six seasons from a Velocity A23 OC rim.

I do volume riding and races on the MTB, and do intervals mostly on the RB since it has the PM.

There was a recent study saying accuracy of intervals isn't too important. But _doing_ them is important. So the extra OCD might not be worth the money.


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## bootsie_cat (Nov 3, 2004)

Power2max makes powermeters that fit a variety of cranks. Raceface, SRAM, Rotor, Shimano, etc.

I had a Power2max on an Easton crank for my gravel bike. Function was flawless.


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## HyperSprite (Mar 14, 2014)

I've got PM's on all my bikes (don't judge, I've slowly collected them over time). 

Started with a Powertap and sold it for Power2Max S-type on my road bike. Great but because its mounted to a narrow Specialized BB30 crank, options for moving it are limited. The new ones are better with USB charging, my older one required the cranks be removed from the bike to change the battery. It last a long time but it's a total pain.

Stages v1 on my old mtb with XTR cranks, spikes bad if I'm descending. This screws up my power graph with 2000w 1 second spikes and ridiculous TSS calculations. Batteries are probably dead every other time I take it out. Could be moved to another bike, but the arm looks like it's been through a war (rock strikes and shoe rub).

Stages v2 on my gravel bike with Sram Force crank. I thought it would be better than the v1 with the spikes and battery. Nope. Because the cranks allow for direct mount chainrings, at least it has that going for it.

D-Zero on XX1 Dub. Arrived, didn't clear my frame, returned, so I don't have any exp with that one.

Cinch on my new mtb with Raceface Next SL g5 cranks. Of these, this is my favorite because:
Pros
I can use any raceface style direct mount chainring and they are not hard to swap.
No clearance problems.
It charges via USB and seems to last a while between charges (I've had it 3 months and only charged it when I got it). 
Crank arms come in a wide size/price range.
Seems safe from damage inside the BB.
Price was reasonable.
BB92 version I bought should be compatible if I want to move it to another bike (at least I hope so).
No 2000w power spikes on descents

Cons
Really just a left side measurement (still reads the same as my dual side Power2max when I compare my efforts, so it doesn't bother me).

It might be reasonable to move a Cinch between bikes but it would depend how often.


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## waltaz (Oct 14, 2004)

Great feedback; thank you all. I appreciate it!


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## bloodninja (Jul 11, 2012)

HyperSprite said:


> Cinch on my new mtb with Raceface Next SL g5 cranks. Of these, this is my favorite because:
> Pros
> I can use any raceface style direct mount chainring and they are not hard to swap.
> No clearance problems.
> ...


Ahh man you had me sold on the Cinch until I realized it was left side only.

I hate to keep plugging a product that's not out yet, but I have high hopes for the SRM X-power. If it works well, I'm gonna use it on every bike...even my road bike.


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## Sidewalk (May 18, 2015)

I would say I am highly invested in PM's, but luckily got them all heavily discounted so I don't feel so bad. PM's on 4 bikes (Vector, Stages, and Cinch). 

Really, besides the geeking on numbers, they were probably a waste of money for me. At least right now. If I change my training methods in the future to an ultra low hour method where hitting target numbers is more important, than maybe. But right now, it doesn't do me any good.


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## jtsoderman (Sep 12, 2013)

bootsie_cat said:


> Power2max makes powermeters that fit a variety of cranks. Raceface, SRAM, Rotor, Shimano, etc.
> 
> I had a Power2max on an Easton crank for my gravel bike. Function was flawless.


I've got a P2M on my MTB, Quarq on the road bike and a second P2M on the TT. All are great reliable etc. I think a PM for road or trainer riding is much more useful than for MTB. The riding is so much more on/off from an effort perspective the info just isn't as useful. What I've found is that the PM is most helpful for being sure I do my intervals correctly, which is much more productive on the road/trainer. All that said, I still nerd out over the MTB data...


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## careyj1 (May 12, 2017)

I just installed a 4iii on the right ride (drive side) on my Tall Boy. The took the crank arm off and mailed it to them, they installed the powermeter and send it back to me. It works well. I compared the numbers to the S works dual sided powermeter on my road bike and the numbers seem to be similar.


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## mtb_phd (Jun 28, 2017)

I get asked this a lot so I wrote an article about it!
https://smartmtbtraining.com/articles/picking-the-right-power-meter-for-mountain-bike-racing


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## Brad (May 2, 2004)

I would not recommend the PowerTap Hub as its at the back end of the drive system. The torque it will register to calculate power is high;y variable off road.

I would suggest a crank based unit of sorts since this measures twist in the crank arm due to the force yo apply to it. Ultimately the traction will play a role but not as much as it would for the Powertap to give meaningful results. Not sure what type of crank you have but most are easily transferable from bike to bike with an allen key fitted to a torque wrench.

If you have Shimano Cranks then he Stages or 4iiii Precision PM's are good.
For crank based Power2max and Quarq are the standard.

when conducting intervals out on the trail it will be critical for your plan that you identify regular routes that you can use consistently to conduct your drills on.
Set your head unit to 10s averaging otherwise your will be chasing your tail trying to stay in the correct zone.
And learn to work with Normalised power and average power as staying in a zone is going to be extremely challenging anyway


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## Lone Rager (Dec 13, 2013)

Brad said:


> I would not recommend the PowerTap Hub as its at the back end of the drive system. The torque it will register to calculate power is high;y variable off road. I would suggest a crank based unit of sorts since this measures twist in the crank arm due to the force yo apply to it. ...


You can't apply torque to the crank unless there is something resisting spinning the crank. The only thing that can resist it is the rear hub. If the cassette is spinning freely on the hub, the crank will spin freely and though you can spin the crank, you can't apply torque or generate power. Aside from the minor losses in the drivetrain, I don't see how power measurement at the hub can differ from that at the crank.

I'm not arguing for against hub or crank based power. I just don't believe they'll be consequentially different.


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## WR304 (Jul 9, 2004)

bloodninja said:


> I hate to keep plugging a product that's not out yet, but I have high hopes for the SRM X-power. If it works well, I'm gonna use it on every bike...even my road bike.


I reckon the SRM X-Power pedals are going to be a disaster as pedal bodies are quite an exposed part of the bike and take some hard hits. The first time you're at the top of a scree slope, watching your bike cartwheeling off down through the rocks without you onboard will be the real test of them!

Power pedals are also notoriously difficult to make work and be reliable as power meters to begin with even as road pedals. Just look at Garmin who are up to Version 3 of their Vector pedals and even so have many problems.

https://www.dcrainmaker.com/2019/09...meter-first-look-a-turning-point-for-srm.html

I went and had a look back through some historic rides when I had a Powertap hub (2010 to 2012). There was a lot wrong with it (don't even get me started on the virtual cadence or the reliability issues that saw a failure and out of warranty new torque tube every season) :madman: but to be fair the actual power data it provided riding offroad always looked ok and consistent between on and offroad. It wasn't like it had a meltdown as soon as you left the tarmac.

Stages and 4iiii power meters are crank arm based and can create false power spikes in your data when riding offroad on rough surfaces, particularly downhill. My friend has a 4iiii on his gravel bike and I always have fun emailing him to let him know that he didn't actually pedal at 1,680 watts in the Brecon Beacons after every ride! That's a very recent crank too, only a few months old, so it hasn't improved much. From a quick look at some of his rides the 4iiii tends to have issues with initial bursts, going from not pedalling to starting pedalling, possibly when the initial pedal stroke isn't smooth or a complete rotation, which results in a massive power spike and false cadence (eg: 172rpm cadence and 1,123 watts for 1 second, the next second being 52rpm cadence and 219 watts).

The crank spider based power meters like Power2Max, Quarq and SRM are generally about as good as it gets offroad. They tend not to get power spikes and can usually stand up to wet weather without failing.


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## Brad (May 2, 2004)

In my experience they are. The Crank isn't affeced by the chain unloading repeatedly as the bike rides over bumps and jumps. The Crank is not affected by tyre impacts that deliver spikes in the data. Powetap have done well to filter noise but I always ended up with higher NP and lower average power values than with either a stages, p2m or quarq. I settled on the p2m eventually.
I've just read through the smart mtb training article and they talk to a similar experience. Also explains why the power tap mtb hub isn't very popular anymore.

The p2m, stages. PT hub and sort of half a quarq were the only solutions I could get that worked on the scalpel Ai. The hub based unit really stood out as not giving consistent results once out in the mountain single-track. It was right there with the others on the tar and gravel roads but once we hit the technical stuff it was out and inconsistently so


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## richde (Jun 8, 2004)

WR304 said:


> Power pedals are also notoriously difficult to make work and be reliable as power meters to begin with even as road pedals. Just look at Garmin who are up to Version 3 of their Vector pedals and even so have many problems.
> 
> https://www.dcrainmaker.com/2019/09...meter-first-look-a-turning-point-for-srm.html


FYI: There's an easy fix for the Garmin pedals, since the problem seems to be that the inner battery connection tab just doesn't have enough spring tension....you slide a little something (slice of wine cork) under the tab and the problems disappear.

Should it need that fix? Of course not, but it does fix it and pedal power meters are a great idea for the road, although very bad for off road.


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## bloodninja (Jul 11, 2012)

WR304 said:


> I reckon the SRM X-Power pedals are going to be a disaster as pedal bodies are quite an exposed part of the bike and take some hard hits. The first time you're at the top of a scree slope, watching your bike cartwheeling off down through the rocks without you onboard will be the real test of them!


I bought a set of Favero Assioma pedals for my road bike, and they've been flawless. Being able to easily swap from one bike to another is such an advantage that it's worth the risk since they're supposed to retail for only $999. The pedal body is supposed to be replaceable.


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## J.B. Weld (Aug 13, 2012)

bloodninja said:


> I bought a set of Favero Assioma pedals for my road bike, and they've been flawless. Being able to easily swap from one bike to another is such an advantage that it's worth the risk since they're supposed to retail for only $999. The pedal body is supposed to be replaceable.


Pedal strikes are pretty rare in road biking but common on the mtb. I think power meter pedals are a great idea for the road but seem like a bad idea for the trail. I think a crankarm based one would be best.


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## Lone Rager (Dec 13, 2013)

^^^ agree. I'd wait a bit on mtb pedal power meters until there's more user experience out there to see how they hold up against pedal strikes. 

FWIW: Assioma Duo pedals are $650.


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## bloodninja (Jul 11, 2012)

J.B. Weld said:


> Pedal strikes are pretty rare in road biking but common on the mtb. I think power meter pedals are a great idea for the road but seem like a bad idea for the trail. I think a crankarm based one would be best.


I'm counting on the SRM engineers knowing more about this stuff than you guys


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## WR304 (Jul 9, 2004)

Brad said:


> In my experience they are. The Crank isn't affeced by the chain unloading repeatedly as the bike rides over bumps and jumps. The Crank is not affected by tyre impacts that deliver spikes in the data. Powetap have done well to filter noise but I always ended up with higher NP and lower average power values than with either a stages, p2m or quarq. I settled on the p2m eventually.
> I've just read through the smart mtb training article and they talk to a similar experience. Also explains why the power tap mtb hub isn't very popular anymore.
> 
> The p2m, stages. PT hub and sort of half a quarq were the only solutions I could get that worked on the scalpel Ai. The hub based unit really stood out as not giving consistent results once out in the mountain single-track. It was right there with the others on the tar and gravel roads but once we hit the technical stuff it was out and inconsistently so


I think that the explosion of new entrants into the power meter market over the last decade, often at drastically lower price points, really cut into the popularity of Powertap hubs. Being able to just put a left hand crank or some pedals on without having to mess around with having a rear wheel built etc has been a real game changer.

In terms of the mountain bike Powertap hubs they were extremely slow to react to the changes of rear wheel standards, 142x12mm thru axles were years behind, then the move to 148x12mm boost hubs left them behind again. At the time of writing 14 November 2019 there isn't even a 148x12mm boost Powertap MTB hub available and 148x12mm Boost has been standard on most new MTB XC bikes for at least 2 years by now which makes them a non option. Even if I wanted to put one on my new 2020 Orbea Oiz with its 148x12mm Boost hub spacing for example I couldn't.

https://www.quarq.com/product/powertap-g3-disc-hub/

When I had a Powertap hub (RIP) I didn't have anything else to run it against simultaneously.

As a big picture overview here's a look at a six month slice of my riding from 01 January 2011 to 30 June 2011 Powertap MTB hub compared to 01 January 2017 to 30 June 2017 Power2Max Type S crank power meter. I did 100 hours more riding in the first six months of 2017 than in 2011 (369 hours 2017 to 266 hours 2011) so my fitness wasn't too bad but you can see that even so I was nowhere near close to the short term power figures recorded by the Powertap hub. 2011 Peak 5 second power 590 watts, 2017 Peak second power 507 watts. There are lots of various factors to consider but it's fairly clear to me that my Powertap hub read high at short durations. I was slow enough to begin with without losing all my watts! :cryin:

I have run my Power2Max Type S crank against a Tacx Neo turbo trainer (and also my Power2Max Classic crank against the Tacx Neo) and overlaid the data from the two and they were all close so the Powertap hub looks to be the outlier.

Anyway, that's a long winded and poorly worded way of saying that no I wouldn't recommend a Powertap hub.


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## WR304 (Jul 9, 2004)

bloodninja said:


> I'm counting on the SRM engineers knowing more about this stuff than you guys


SRM do have some prior pedal history already with the SRM Exakt road pedals. Those aren't the same as the unreleased SRM X-Power MTB pedals but don't get a glowing review:

https://www.dcrainmaker.com/2018/12/srm-exakt-power-meter-pedals-in-depth-review.html

On a general point the pedal bodies are SPD compatible but aren't actually Shimano SPD. From the other "SPD compatible" but not made by Shimano pedals I've had in the past I far prefer to have a proper Shimano SPD pedal and Shimano cleat underfoot for clipping in and out with when riding.


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## Brad (May 2, 2004)

For the road Assioma is simply the best value for money product in the OM space. It’s reliable, easy to set up and tracks well across a wide power output range. It’s easily the best pedal based system. Would I use a pedal based system on a mtb? No way!i pedal through everything. My TIME pedals are battered and bruised. I can’t see strain gauges holding up reliably to that sort of continuous abuse


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## Lone Rager (Dec 13, 2013)

bloodninja said:


> I'm counting on the SRM engineers knowing more about this stuff than you guys


Yep. I figure marketing said, "There's market opportunity for mtb power pedals because nobody else is doing it." Engineering said, "There's a good reason for that." Management said, "Do it anyway." Engineering said, "OK, here's the best we can do but we still have concerns." Management, "Goody. Sell them."


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## J.B. Weld (Aug 13, 2012)

bloodninja said:


> I'm counting on the SRM engineers knowing more about this stuff than you guys


I don't know anything, just stating a hunch. My spd's get beat to $hit. Hopefully those SRM's will be great, at least for your sake.


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## Sidewalk (May 18, 2015)

All I have to do is look at my crank arms and know that power based pedals are a bad idea. The couple of broken pedals (and broken crank arm) are also good telltale signs.


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## TDLover (Sep 14, 2014)

That's the same reason carbon cranks are a bad idea, yet you still find plenty of people who defend them fiercely. You also find anecdotes of people who claim they last longer than aluminum, strikes included. Some people are fine if they last a season, maybe 2, so in their logic these products are perfectly reasonable given the advantages and disadvantages they have.


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## richde (Jun 8, 2004)

J.B. Weld said:


> I don't know anything, just stating a hunch. My spd's get beat to $hit. Hopefully those SRM's will be great, at least for your sake.


It's very possible to break the retention portion of an SPD pedal, and we've probably all seen bent Crank Bros...

I'm pretty happy with my Vectors on my road bike, but just got a Quarq for my MTB. I'd be a little wary of typical crank based power as well, since bouncing rocks do like to find the expensive bits and if that pod is on the forward pedal....


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## Lone Rager (Dec 13, 2013)

For crank based there're crank arm, spider, and spindle PMs. I'm running a spindle PM but would think they'd all be much more resistant to rock strike ramifications than pedal PMs.


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## Brad (May 2, 2004)

I've heard some truly bizarre impact failures related to Crank based pm's, but I believe those people also tend to walk into closed doors and trip over their shoe laces. To break a quarq battery compartment takes a special kind of bad luck, especially if you get it right without breaking your leg.
p2m.... Jerez you'd need to have someone intentionally shoot at it to break it via trail impact.
Pedals..... My box of failed products is filled with pedals including xtr m980 with Ti axles. Numerous spd failed mechanisms. I wish SRM all the best with their marketing venture


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## Skier78 (Jun 10, 2016)

On my mtb I have a Power2max Ngeco (on a sram x01 crank) and on my cyclocross I have an older Quarq Riken, both have been flawless for me, with fairly long intervals for battery changes and no issues with strange readings.

A couple of years ago I had a Stages on the mtb (second generation I think) but sold it due to a lot of problems with power spikes when going downhill. For me the Power2max is the best choice, fairly low price for a dual sided measurement and they have been around for some time now as well, so reliability seems to be ok.


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## bloodninja (Jul 11, 2012)

LOL, I can't believe you guys have such strong opinions about something that's not even out yet. I've never broken a pedal or crank arm, but I guess if you're breaking them regularly then it's not the product for you. As long as they're accurate and handle potential power spikes or whatever from pedal strikes then I'll take the risk since they're only $999 and if I get 2 seasons out of them I'll be happy.


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## bloodninja (Jul 11, 2012)

One other thing... I'm not that knowledgeable about crank and BB standards and thought that the Quark XX1 carbon was the only PM that would fit my bike. I didn't want that crankset, but I found out in the last week that a P2M spider would work. If the SRM gets delayed past Jan-Feb, I'll probably just pick up the P2M.


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## Lone Rager (Dec 13, 2013)

bloodninja said:


> LOL, I can't believe you guys have such strong opinions about something that's not even out yet...


Not strong opinions, just reservations based on experience bashing pedals. I think they're great idea (as are road power pedals) as long as they're demonstrated to hold up to the type of abuse mtb pedals can be subjected to.


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## WR304 (Jul 9, 2004)

bloodninja said:


> One other thing... I'm not that knowledgeable about crank and BB standards and thought that the Quark XX1 carbon was the only PM that would fit my bike. I didn't want that crankset, but I found out in the last week that a P2M spider would work. If the SRM gets delayed past Jan-Feb, I'll probably just pick up the P2M.


What bike have you got? You should be able to fit a Shimano crankset to more or less any frame by replacing the bottom bracket. The same goes for any crank with a 24mm diameter axle (the same bottom bracket type as Shimano) such as the 24mm diameter axle Race Face or Rotor cranks.

The newer style Shimano 12 speed 1X cranks all have removable spiders so can take a Power2Max crank spider. The Power2Max crank spiders are standard 104BCD (bolt circle diameter) so you can then fit your own choice of narrow wide SRAM or Shimano compatible chainring on there for drivetrain compatibility.

For my Orbea Oiz I've got a Power2Max NG Eco Shimano spider and a Wolftooth Shimano Dropstop 34 tooth round chainring

Power2Max NG Eco Shimano spider
https://www.power2max.com/en/product/ngeco-mtb-shimano-power-meter-spider/

Wolftooth Shimano 104bcd Dropstop chainring
https://www.wolftoothcomponents.com...-chainring-for-shimano-12spd-hyperglide-chain

That setup runs fine with your choice of crank SLX/ XT or XTR and the new style Wolftooth chainring seems to have no issues with the quick link on the new Shimano 12 speed chain.

That's about as far as my new bike has got as Shimano have shortened the axle length on their new chainsets compared to the older ones, which isn't good for swapping in my custom left crank as it doesn't fit on the new cranks.:madman:

Zero Watts! :eekster:


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## variant13 (Jul 7, 2019)

I have have had an excellent experience with a Quarq on SRAM DUB crank/DUB bb.




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## waltaz (Oct 14, 2004)

Hi all...thanks again for all the valuable info!

The bike I want to (initially) add a power meter to is my Yeti SB100, which has a SRAM Dub PF92 BB and SRAM X01 cranks. In the SB100 thread, it was noted that the Stages Carbon GXP crank-arm power meter doesn't clear the SB100's chainstay, so I looking to go with the Power2Max NGECO SRAM spider, with a Wolftooth chainring.

As a quick compatibility check, this is the correct power meter for my SB100, right? Assuming, of course, that I want the Power2Max...

TIA!


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## waltaz (Oct 14, 2004)

WR304 said:


> What bike have you got? You should be able to fit a Shimano crankset to more or less any frame by replacing the bottom bracket. The same goes for any crank with a 24mm diameter axle (the same bottom bracket type as Shimano) such as the 24mm diameter axle Race Face or Rotor cranks.
> 
> The newer style Shimano 12 speed 1X cranks all have removable spiders so can take a Power2Max crank spider. The Power2Max crank spiders are standard 104BCD (bolt circle diameter) so you can then fit your own choice of narrow wide SRAM or Shimano compatible chainring on there for drivetrain compatibility.
> 
> ...


Excellent info; thanks!


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## waltaz (Oct 14, 2004)

bloodninja said:


> One other thing... I'm not that knowledgeable about crank and BB standards and thought that the Quark XX1 carbon was the only PM that would fit my bike. I didn't want that crankset, but I found out in the last week that a P2M spider would work. If the SRM gets delayed past Jan-Feb, I'll probably just pick up the P2M.


I was also eyeing that SRM, but decided to go with the P2M.


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## Walt Disney's Frozen Head (Jan 9, 2008)

Given the type of riding you do it'd be a good idea to pick up a few extra battery covers (imo) as sometimes they just seem to disappear. I still love this PM despite that issue.


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## zgxtreme (Mar 25, 2007)

Ok so I’ve admittedly not looked into the P2M, always directing my interest in a Quarq. 

Can an ECO model install directly to the Truvativ (presuming SRAM model P2M?) with the SRAM ring on my new Top Fuel? Or I need to upgrade crank as well if I were to pursue this more cost effective solution?


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## WR304 (Jul 9, 2004)

waltaz said:


> Hi all...thanks again for all the valuable info!
> 
> The bike I want to (initially) add a power meter to is my Yeti SB100, which has a SRAM Dub PF92 BB and SRAM X01 cranks. In the SB100 thread, it was noted that the Stages Carbon GXP crank-arm power meter doesn't clear the SB100's chainstay, so I looking to go with the Power2Max NGECO SRAM spider, with a Wolftooth chainring.
> 
> ...


If you've got a SRAM X01 boost dub crankset with the 3 bolt direct mount spider you'd want a Power2Max NGeco MTB SRAM single power meter (boost) €590 euro

https://www.power2max.com/en/product/ngeco-mtb-sram-single-power-meter-boost/

For the chainring it's a standard 104BCD sizing so you could use a Wolftooth 104 BCD Dropstop narrow wide chainring (you're not restricted to just Wolftooth so Praxis, Absolute Black etc 104BCD chainrings should fit too)

https://www.wolftoothcomponents.com...products/104-bcd-chainrings?variant=303173223

You can also fit a SRM spider to the same SRAM X01 crank if you wanted an SRM power meter spider instead of Power2Max €1079.20 euro:

Home page

There is also the more expensive Power2Max NG power meter which fits too €990 euro

https://www.power2max.com/en/product/ng-mtb-sram-single-power-meter-boost/

For the €400 euro price difference between the Power2Max NG Eco and NG you get a rechargeable battery in the NG, the power balance metrics (which don't mean much on a crank spider as it's an estimate) and supposed to be higher accuracy. For me I decided I'd rather have a Power2Max NG Eco as it has a replaceable battery. Rechargeable batteries don't always age well (losing charge as they get older with use as in mobile phones) so being able to put a fresh battery in when needed was more appealing to me.

I haven't got my Power2Max NG Eco spider here (it's at my mate's factory waiting for a crank to put it on) but the battery cover is different to the older models in that it is a rubber push on cover. When ordering I got a spare battery cover at the same time.

The Power2Max NG Eco broadcasts on ANT+ and Bluetooth. When you get it you have to pair it via a mobile phone to register the power meter and update the firmware. You have a red sticker attached to the power meter with a Serial Number and Activation Token on that you use.

This was a lot harder than it should have been. Here's how I did it eventually:

Step 1: Go to the Power2Max app portal web page and setup a new account on there (this is different to the shopping account for purchasing from Power2Max)

https://apps.power2max.com/portal/index.php

Step 2: Once you have a new account go to Manage powermeters and enter your Serial Number and Activation Token number into the webpage so it shows as registered to you.

Step 3: Using an ANDROID phone such as a Samsung Galaxy go to the Google Play Store, download and install the Power2Max app to the phone. I originally tried this on my Apple iPad but it was only after I switched to the Android version of the Power2Max app that I could make it register.

Step 4: Wake up the Power2Max spider by spinning it so the light flashes, have Bluetooth turned on on the phone, hold the phone extremely close to the spider and do the search for new devices on the Power2Max app. When the Power2Max spider shows up on the list in the app tap on it and then enter the serial number and activation token when prompted in the app. This took probably 5 and 10 tries with it being rejected until the registration worked.

Step 5: Now it's registered that should be it. I was then able to update the firmware through the Power2Max android app and it would also connect to the Power2Max app on my Apple iPad and display the information for the spider.

Pictured below: The red sticker with Activation Token and Serial Number that comes with a new Power2Max NG Eco

A screenshot of the Power2Max app portal webpage for registering the power meter.


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## WR304 (Jul 9, 2004)

zgxtreme said:


> Ok so I've admittedly not looked into the P2M, always directing my interest in a Quarq.
> 
> Can an ECO model install directly to the Truvativ (presuming SRAM model P2M?) with the SRAM ring on my new Top Fuel? Or I need to upgrade crank as well if I were to pursue this more cost effective solution?


Which Truvativ crank is it? The new Eagle ones look to be SRAM cranks in all but name with DUB axle sizing and direct mount chainrings that have SRAM stamped on them. The way to check is to look at the inside of the driveside crank and see if the direct mount chainring is held on with three bolts.

https://www.sram.com/en/truvativ/models/fc-styl-c-b1

This is the compatibility list that Absolute Black have for their SRAM compatible direct mount chainrings. This includes Truvativ cranks so it sounds like you could switch the spider to a power meter spider: 

https://absoluteblack.cc/xx1-style-sram.html

*Absolute Black SRAM Boost direct mount chainring compatibility list:*
SRAM AXS, XX1, XX1 Eagle, X01, X01 Eagle, GX Eagle, NX Eagle, SX Eagle, X1, X0, X9, X7, S2210, S1400, Descendant, Stylo, Truvativ AKA and all DUB cranks.Cane Creek eeWings. GXP and Long spindle BB30. BOOST148 bikes ONLY. 9, 10, 11 and 12spd Eagle compatible.


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## waltaz (Oct 14, 2004)

WR304 said:


> If you've got a SRAM X01 boost dub crankset with the 3 bolt direct mount spider you'd want a Power2Max NGeco MTB SRAM single power meter (boost) €590 euro
> 
> https://www.power2max.com/en/product/ngeco-mtb-sram-single-power-meter-boost/
> 
> ...


This is incredibly helpful; thank you very much for the detailed info!


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## bloodninja (Jul 11, 2012)

2020 Top Fuel? That's the same bike I have. I emailed P2M and they confirmed that it would work.


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## zgxtreme (Mar 25, 2007)

bloodninja said:


> 2020 Top Fuel? That's the same bike I have. I emailed P2M and they confirmed that it would work.


Yeah, a 2020 9.8. Good to hear.


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## Brad (May 2, 2004)

zgxtreme said:


> Ok so I've admittedly not looked into the P2M, always directing my interest in a Quarq.
> 
> Can an ECO model install directly to the Truvativ (presuming SRAM model P2M?) with the SRAM ring on my new Top Fuel? Or I need to upgrade crank as well if I were to pursue this more cost effective solution?


Truvativ carbon and alloy cranks have the three bolt mount. The axle whether bb30 or dub or gxp doesn't matter. They use the same three bolt interface as the direct mount chain rings. 
Only quarq cranks have the 8 bolt mount and same OEM road cranks that all PM ready. 
You order the P2M for SRAM in the boost version. Well doesn't matter if you order boost or standard as the standard is a boost with a spacer in the box to mount the chainring in the 6 mm offset position.


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## euro-trash (Feb 9, 2008)

MTB powermeter pedal hack if anyone is interested:


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## WR304 (Jul 9, 2004)

Here's a look at my completed Power2Max NGeco power meter.









It's a Shimano Deore XT M8100 right hand crank with a Power2Max NGeco spider and Woftooth 34 tooth round chainring. That was supposed to be it, no modification needed, but Shimano have shortened the axle and slightly altered the splines on their newer cranksets. These things are never straightforwards.









In order to make it work the steel crank axle was wire cut in half and then half a Shimano Deore Crank axle with the correct spline and length for a Shimano Deore Crank was attached to it. In this picture the piece of metal at the bottom shows the test cut. The axle has a reinforcing steel sleeve inside and a bolt through the middle so there's no way this is coming apart when riding!

That means I can attach my custom swing crank, based on a Shimano Deore left hand crank, to the Shimano Deore XT right hand crank making the bike fully rideable at last.


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## DrewBird (Apr 11, 2007)

WR304 said:


> Here's a look at my completed Power2Max NGeco power meter.


Nice work, looks like a solid and well-executed solution.

Just to be clear, this modification was only needed to fit your custom left-side crank arm, correct? Not because of incompatibility between the P2M unit and the 12-speed cranks?

I'm running Shimano FC-MT900 cranks (which I wholeheartedly recommend; these are the "temporary" XTR cranks, currently being blown out for $150 with chainring at Jenson. 40g heavier and ~$400(!) cheaper than the XTRs). Hoping a P2M will fit these without drama.


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## TDLover (Sep 14, 2014)

DrewBird said:


> I'm running Shimano FC-MT900 cranks (which I wholeheartedly recommend; these are the "temporary" XTR cranks, currently being blown out for $150 with chainring at Jenson. 40g heavier and ~$400(!) cheaper than the XTRs). Hoping a P2M will fit these without drama.


Those cranks will be a relic in the future I almost want to buy them to keep them for collection. Unmarked, xtr chainring and cheap.


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## DrewBird (Apr 11, 2007)

TDLover said:


> Those cranks will be a relic in the future I almost want to buy them to keep them for collection. Unmarked, xtr chainring and cheap.


Yeah crankset with chainring is $30 more than just buying the XTR chainring alone.


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## WR304 (Jul 9, 2004)

DrewBird said:


> Nice work, looks like a solid and well-executed solution.
> 
> Just to be clear, this modification was only needed to fit your custom left-side crank arm, correct? Not because of incompatibility between the P2M unit and the 12-speed cranks?
> 
> I'm running Shimano FC-MT900 cranks (which I wholeheartedly recommend; these are the "temporary" XTR cranks, currently being blown out for $150 with chainring at Jenson. 40g heavier and ~$400(!) cheaper than the XTRs). Hoping a P2M will fit these without drama.


There's no incompatibility between the 12 speed Shimano cranks and the Power2max spider. The modification to my crank was just the axle splines to fit the custom left hand crank on.

You'll need a Shimano TL-FC41 lockring tool for undoing the lockring to swap the chainrings over.

If you've bought a seperate chainset it will probably have been included with it. I didn't get one with my complete bike but it did come with the XT cranks.









From what I've read the temporary Shimano MT900 cranks are the same as what is now called the Shimano Deore XT crank, just without the XT branding.


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## DrewBird (Apr 11, 2007)

WR304 said:


> From what I've read the temporary Shimano MT900 cranks are the same as what is now called the Shimano Deore XT crank, just without the XT branding.


Great, thanks for the info. I did receive that tool with the MT900s. And I believe you're right, they're blacked-out XT arms with and XTR chainring.


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## KingOfOrd (Feb 19, 2005)

Wahoo recently acquired Speedplay, makes me think we'll see some new power meter pedals on the market from Wahoo soon. I know they're not favorable for mountain biking, but we could still see some cool things coming out in the future.


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## Brad (May 2, 2004)

Train Wreck said:


> Wahoo recently acquired Speedplay, makes me think we'll see some new power meter pedals on the market from Wahoo soon. I know they're not favorable for mountain biking, but we could still see some cool things coming out in the future.


Speedplay MTB pedals were a dismal failure so I hope they first address the mechanical design before adding a PM to a poor design


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## HyperSprite (Mar 14, 2014)

Brad said:


> Speedplay MTB pedals were a dismal failure so I hope they first address the mechanical design before adding a PM to a poor design


There is 0 market for a Speedplay MTB based PM. If Wahoo's making a PM it will be road only.


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## DrewBird (Apr 11, 2007)

HyperSprite said:


> There is 0 market for a Speedplay MTB based PM. If Wahoo's making a PM it will be road only.


Or pedal-based MTB PM in general. With the abuse MTB pedals take this approach is pretty much a non-starter I think.


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## KingOfOrd (Feb 19, 2005)

With all the gravel riding these days I think there could be demand for a power pedal that is not road specific.


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## DrewBird (Apr 11, 2007)

Train Wreck said:


> With all the gravel riding these days I think there could be demand for a power pedal that is not road specific.


Fair point! I forget about the "emergence" of gravel being the current driving force in bike design (apparently?)

Still seems like the pedal is an awfully vulnerable (and stealable!) place to put a $$ piece like a PM. But what do I know, I've been riding around on gravel roads for years on a NON-GRAVEL SPECIFIC BIKE like some kind of idiot.


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## L.Rodriguez (Jul 22, 2008)

Hi !
Please, could someone indicate some PM for the E'13 XLC carbon MTB crankset ?
This cranks assembly in S.C. Blur 2019 with CB Eggbeater pedals.
I cannot see any options, and the HIVE guys don't see...
POWER/AERO POD would it be a good option ?
Thanks in advance !


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## bootsie_cat (Nov 3, 2004)

Sell E-13 on ebay and get a Quarq, P2Max or SRM. 
P2Max and SRM now make powermeter chassis' that are native for XTR 9100 cranks!



L.Rodriguez said:


> Hi !
> Please, could someone indicate some PM for the E'13 XLC carbon MTB crankset ?
> This cranks assembly in S.C. Blur 2019 with CB Eggbeater pedals.
> I cannot see any options, and the HIVE guys don't see...
> ...


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## mtb_phd (Jun 28, 2017)

L.Rodriguez said:


> Hi !
> Please, could someone indicate some PM for the E'13 XLC carbon MTB crankset ?
> This cranks assembly in S.C. Blur 2019 with CB Eggbeater pedals.
> I cannot see any options, and the HIVE guys don't see...
> ...


The Aero Pod won't work for MTB due to the different riding surfaces (it will think you are putting out less power if you ride off of a road and on to grass, for example)


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## Lone Rager (Dec 13, 2013)

Check out the Team Zwatt Yding power crank. That's what I'm running.

https://teamzwatt.com/products/yding-carbon-mtb-power-meter/


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## WR304 (Jul 9, 2004)

L.Rodriguez said:


> Hi !
> Please, could someone indicate some PM for the E'13 XLC carbon MTB crankset ?
> This cranks assembly in S.C. Blur 2019 with CB Eggbeater pedals.
> I cannot see any options, and the HIVE guys don't see...
> ...


The E*13 XLC cranks appear to be an ebike model. Is it an E*13 XCX carbon crank?

https://www.ethirteen.com/collections/all-cranks/products/xcx-race-carbon-cranks

The E*13 cranksets use a 30mm spindle and have a removeable direct mount chainring but use their own dedicated spline for attaching the chainrings to the crank. There are aftermarket chainrings from manufacturers such as Absolute Black for that spline but no power meter spiders that I can see.

What I'd suggest would be to get a different chainset that can take a power meter spider. The swingarm layout on the Santa Cruz Blur looks like it could potentially interfere if you were to get a left hand crank power meter such as a Stages or 4iii so a spider based power meter would be most likely to fit.

Quarq used to do 30mm spindle cranks that would drop straight in but as they've gone to SRAM Dub (28.99mm spindle :madman: ) you'd need to replace the bottom bracket as well as the cranks for a Quarq. It's doable but would need a DUB bottom bracket.

If you really want to keep the current bottom bracket you could get some Praxis Lyft M30 30mm spindle carbon cranks and a Power2Max NG Eco spider to fit.

https://praxiscycles.com/product/lyft-m30-thru/

https://www.power2max.com/en/product/ngeco-mtb-praxis-single-power-meter-boost/

.


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## AMessy (Jun 30, 2004)

WR304 said:


> Here's a look at my completed Power2Max NGeco power meter.


Could you please state what chainring bolts you are using?

I have the same crank, power meter, chainring (although 32T) combo as you. It seems the 6mm wolftooth chainring bolts are too long and bottom out before the chainring is fully tightened to the spider. There is a tiny bit of play felt. It almost seems as if this combo needs a shorter chainring bolt than what wolftooth provides for 1x chainrings.

I appreciate your feedback and data point for A compatible chainring bolt.


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## WR304 (Jul 9, 2004)

AMessy said:


> Could you please state what chainring bolts you are using?
> 
> I have the same crank, power meter, chainring (although 32T) combo as you. It seems the 6mm wolftooth chainring bolts are too long and bottom out before the chainring is fully tightened to the spider. There is a tiny bit of play felt. It almost seems as if this combo needs a shorter chainring bolt than what wolftooth provides for 1x chainrings.
> 
> I appreciate your feedback and data point for A compatible chainring bolt.


I bought the Power2Max NG Eco crank spider, chainring and chainring bolts all at the same time from Power2Max.

The chainring bolts that it came supplied with by Power2Max were Rotor alloy bolts, rather than Wolftooth.









In order to get the Rotor chainring bolts tight I had to modify a Shimano TL-FC20 chainring bolt tool (the newer version of the tool is Shimano TL-FC21).

https://www.sjscycles.co.uk/tools/shimano-tlfc21-chainwheel-peg-spanner/

This tool is for holding the threaded part at the back of the chainring bolt in place whilst tightening the 5mm allen bolt so the bolt can't spin. As standard the Shimano TL-FC20 chainring bolt tool has an extended middle pin but this meant the two side pins wouldn't hook in place on the short 1x chainring bolts so I cut the middle pin down with a hacksaw. This tool allowed the bolts to be fully tightened and in use they haven't come loose.


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## AMessy (Jun 30, 2004)

WR304 said:


> I bought the Power2Max NG Eco crank spider, chainring and chainring bolts all at the same time from Power2Max.


Thanks for the reply and detailed info! I also purchased the power meter, chain ring and bolts as a package, but from Power Meter City versus Power2max direct. I didn't specify the chain ring bolts, only selected the option to have them included.

I'll look into sourcing some of the Rotor branded ones you are using. Ironically I have two modified chain ring bolt wrenches similar to yours laying around in my shop. I'll dig them out. I had the same problem years ago when converting a 2x crank to 1x using some race face chain ring bolts with the pin on the tool being too long.

Thanks again!


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## WR304 (Jul 9, 2004)

AMessy said:


> Thanks for the reply and detailed info! I also purchased the power meter, chain ring and bolts as a package, but from Power Meter City versus Power2max direct. I didn't specify the chain ring bolts, only selected the option to have them included.
> 
> I'll look into sourcing some of the Rotor branded ones you are using. Ironically I have two modified chain ring bolt wrenches similar to yours laying around in my shop. I'll dig them out. I had the same problem years ago when converting a 2x crank to 1x using some race face chain ring bolts with the pin on the tool being too long.
> 
> Thanks again!


As you've already got the Wolftooth alloy chainring bolts the fix would be to shorten the length of the Wolftooth bolts by 0.5 to 1mm, carefully holding them in a vice and using a metal file, enough that they can tighten down fully so there is no play in the chainring.

With alloy bolts it should be a quick job only taking a few minutes.


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## TDLover (Sep 14, 2014)

WR304 said:


> As you've already got the Wolftooth alloy chainring bolts the fix would be to shorten the length of the Wolftooth bolts by 0.5 to 1mm, carefully holding them in a vice and using a metal file, enough that they can tighten down fully so there is no play in the chainring.
> 
> With alloy bolts it should be a quick job only taking a few minutes.


Hah that reminds me of the anecdote from Santa Cruz linkage issues.

Certain customer noticed some play on the rear linkage of his Santa Cruz Blur bike, he then promptly sought help from Santa Cruz, after some emails back and forth the engineer told him he could just shim the bolts from the pivots just a tiny bit to allow for the worn out linkages to sit tight due to the bolt design and length.

The customer was baffled by the solution, he posted it in MTBR trying to ridicule Santa Cruz from suggesting such a simple and barbaric fix. I wasn't one of them at the time, but keyboard experts quickly let him know that it was actually a good solution and shouldn't worry much. At the worst of the cases if he was not up to the task of doing it himself, he could just take it to a shop and let them do it for him.

Which reminds me I've got to do the same thing for mine.


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## AMessy (Jun 30, 2004)

WR304 said:


> As you've already got the Wolftooth alloy chainring bolts the fix would be to shorten the length of the Wolftooth bolts by 0.5 to 1mm, carefully holding them in a vice and using a metal file, enough that they can tighten down fully so there is no play in the chainring.
> 
> With alloy bolts it should be a quick job only taking a few minutes.


I made it work, but decided to go ahead and order some chainrings that have the nut threaded all the way through. The wolf tooth bolts are broached for a 6mm Allan key on the nut, so the bolts were bottoming out.

I taped down some sand paper to a piece of reference granite I have in my workshop and used a drill with appropriate sized Allan key to spin the nut and removed 1mm. I then tried it and there was no difference, chainring was still loose. I then did the same thing with the bolt and took 2mm off. This time the chainring was appropriately tight. Only problem was after removing 2mm of thread from the bolt, and 1mm from the nut I wasn't happy with how much thread was left engaged.

I just went ahead and ordered some Absolute Black bolts that have the nut threaded all the way through and require a specific chain bolt nut wrench to tighten versus an Allan key.


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## WR304 (Jul 9, 2004)

AMessy said:


> I made it work, but decided to go ahead and order some chainrings that have the nut threaded all the way through. The wolf tooth bolts are broached for a 6mm Allan key on the nut, so the bolts were bottoming out.
> 
> I taped down some sand paper to a piece of reference granite I have in my workshop and used a drill with appropriate sized Allan key to spin the nut and removed 1mm. I then tried it and there was no difference, chainring was still loose. I then did the same thing with the bolt and took 2mm off. This time the chainring was appropriately tight. Only problem was after removing 2mm of thread from the bolt, and 1mm from the nut I wasn't happy with how much thread was left engaged.
> 
> I just went ahead and ordered some Absolute Black bolts that have the nut threaded all the way through and require a specific chain bolt nut wrench to tighten versus an Allan key.


It's all good practice.

Interestingly on the Absolute Black chainring bolt product page there's a note down the bottom saying that their chainring bolts may need to be filed down to work with some combinations of chainrings and cranks (1x chainrings on road cranks):

_"Sometimes there may be a need to file down female nuts to achieve proper fit. This is because each crank has tabs of different thickness and it is not possible to make "one fit all" solution. Bolts itself are fine.

MTB users will not have to do any modifications to bolts or nuts."_ *absolute black *

https://absoluteblack.cc/bolts.html

If you do find they need filing down to fit the Power2Max spider I'd take off just small incremental amounts, 0.5 to 1mm at a time, until they tighten properly.


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## WR304 (Jul 9, 2004)

TDLover said:


> Hah that reminds me of the anecdote from Santa Cruz linkage issues.
> 
> Certain customer noticed some play on the rear linkage of his Santa Cruz Blur bike, he then promptly sought help from Santa Cruz, after some emails back and forth the engineer told him he could just shim the bolts from the pivots just a tiny bit to allow for the worn out linkages to sit tight due to the bolt design and length.
> 
> ...


When it comes to doing any proper parts, such as my custom left hand crank above, my friend's engineering company made that for me. I didn't do it myself.

There are quite a lot of bike components, including very expensive ones, that often need something doing to them before they actually work properly. The best example I can think of is frames that come without an open bottom bracket drain hole in the frame to let rain water out. Without that drain hole the bottom bracket bearings end up sat in water after wet rides, drastically reducing their lifespan.

If there isn't an unobstructed drain hole, particularly for UK riding which is very wet, it means getting a drill and making one in a brand new carbon fibre frame!


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## 41ants (Jun 12, 2007)

Lots of great info here. I'm in the market again, as my cinch power meter has now failed me for the 3rd time again. I'll probably end up spending the extra money on a quarq this time around, since I've had great experiences with them on my road and tt bikes.


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## juan_speeder (May 11, 2008)

For mountain biking? 

I don't recommend one at all. All you'll end up with is less money and random numbers to look at. 

If you're gonna train on the road, they make sense, especially if you have miles upon miles of flat roads, or a long climb.

The thing about training with power, is that you do X number of watts for x number of minutes, then repeat. Off road terrain makes that hard to impossible Even if you're trying to ride easy, there's apt to be a section that you have to hit full gas, or you're walking, right? Then there's random bits of downhill on most any climb of note...


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## 41ants (Jun 12, 2007)

juan_speeder said:


> For mountain biking?
> 
> I do't 'recommend one at all. All you'll end up with is less money and random numbers to look at.
> 
> ...


I agree for the most part. Most of my training is doing intervals on my road bike or on the trainer... and in that situation I am looking at the numbers. However, I do like it on the mountain bike for tracking tss and looking at post race numbers or when doing my training laps at the local trails. It's neat to go back and look at lap times compared to power.


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## AMessy (Jun 30, 2004)

WR304 said:


> If you do find they need filing down to fit the Power2Max spider I'd take off just small incremental amounts, 0.5 to 1mm at a time, until they tighten properly.


With the Wolftooth bolts I was going in approximately 0.5 mm increments, but I needed to take the whole 3mm total off (nut and bolt combined) until it actually tightened.

I actually got some final resolution to my issue today. I had emailed Power Meter City the same night I originally posted here to ask if they had any solution. While I still haven't heard back from them I'm assuming they overnighted me a set of replacement bolts because when I got home today I had an envelope from them with a set of the same Rotor Branded bolts you were provided with yours. They worked perfectly, no issues. Installed the Power2Max power meter with no additional issues, updated the firmware and went for a quick ride with my road pedals (Power Tap P1's) to get a quick comparison. Everything tracked similar, so I'm happy. Also I was able to cancel my order for the Absolute Black bolts before they shipped, so I won't have to change to see if they would have worked.

Thanks again for the input and responses.


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## mfa81 (Apr 1, 2011)

41ants said:


> I agree for the most part. Most of my training is doing intervals on my road bike or on the trainer... and in that situation I am looking at the numbers. However, I do like it on the mountain bike for tracking tss and looking at post race numbers or when doing my training laps at the local trails. It's neat to go back and look at lap times compared to power.


this!! tracking tss is important if you want to keep a training log, also racing is fun to look at number. but a decent 10 or 20m climbing gravel road would be more than enough for most interval workouts!


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## WR304 (Jul 9, 2004)

AMessy said:


> With the Wolftooth bolts I was going in approximately 0.5 mm increments, but I needed to take the whole 3mm total off (nut and bolt combined) until it actually tightened.
> 
> I actually got some final resolution to my issue today. I had emailed Power Meter City the same night I originally posted here to ask if they had any solution. While I still haven't heard back from them I'm assuming they overnighted me a set of replacement bolts because when I got home today I had an envelope from them with a set of the same Rotor Branded bolts you were provided with yours. They worked perfectly, no issues. Installed the Power2Max power meter with no additional issues, updated the firmware and went for a quick ride with my road pedals (Power Tap P1's) to get a quick comparison. Everything tracked similar, so I'm happy. Also I was able to cancel my order for the Absolute Black bolts before they shipped, so I won't have to change to see if they would have worked.
> 
> Thanks again for the input and responses.


That's useful to know about the bolts. At least with the Power2Max NG Eco it takes a standard 104BCD chainring, unlike my previous Power2Max Type S double ring powermeter, that can only take now discontinued Rotor chainrings, so there should always be a way to keep it working.

I've been using the Power2Max NG Eco for the last 6 months so have just about enough decent efforts for the Mean Max power curve to be fairly representative now.









This chart shows the Mean Max power curve for my Power2Max NG Eco (18 December 2019 to 09 June 2020 252 hours) against my old Power2Max Type S (05 June 2016 to 03 November 2019 2079 hours). There's enough crossover between the two power curves already that once I have several years of data for the Power2Max NG Eco as well they would be quite close I think. I just need some better form!

Peak 5 second power NG Eco - 492 watts, Type S - 538 watts
Peak 1 Minute power NG Eco - 355 watts, Type S - 372 watts
Peak 5 Minute power NG Eco - 281 watts, Type S - 290 watts 
Peak 20 Minute power NG Eco - 232 watts, Type S - 242 watts
Peak 60 Minute power NG Eco - 212 watts, Type S - 228 watts









This Microsoft Excel graph is a comparison between my Power2Max NG Eco (claimed +/- 2% accuracy) against my Tacx Neo 2T turbo trainer (claimed +/-1% accuracy) for an erg mode interval session recorded in FulGaz. There is 5 seconds smoothing applied to the graph. Even with the 5 seconds smoothing the Power2Max NG Eco data is noticeably more jumpy with up and down swings in power than that from the Tacx Neo 2T. This is why when riding it's usually best to have some power smoothing on the display to make it easier to pace with. Although this graph may look jumpy it's actually more even than you may see from some other power meters.

The Tacx Neo 2T was controlling the target resistance and recording onto my iPad whilst the Power2Max NG Eco was recording onto a Wahoo Elemnt Bolt for the same workout and then the two readings are overlaid on the same graph. The gearing was left in the middle of the cassette with no shifting during the session.









3 min 30 sec NG Eco - 151 watts, Neo 2T - 150 watts
4 min 30 sec NG Eco - 198 watts, Neo 2T - 200 watts
9 min 00 sec NG Eco - 198 watts, Neo 2T - 200 watts
4 min 00 sec NG Eco - 226 watts, Neo 2T - 220 watts
11 min 30 sec NG Eco - 225 watts, Neo 2T - 220 watts

The Power2Max NG Eco seems ok to me accuracy wise. It hasn't had any power spike issues and despite getting soaking wet all last winter has been working reliably every ride so far. Reliability is a massive part of choosing a power meter. If you get something that breaks and drops out all the time or gives bad data it's bad.


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## WR304 (Jul 9, 2004)

Following on from the previous post there was enough battery left in my now retired Power2Max Type S 2016 double ring power meter to do the same interval session as above using that power meter on the Tacx Neo 2T today. This graph shows the Power2Max Type S v the Tacx Neo 2T in erg mode. I left the double chainring on the 38 tooth chainring (being most representative of how it was used) and the middle sprocket on the rear cassette.









3 min 30 sec Type S - 144 watts, Neo 2T - 150 watts
4 min 30 sec Type S - 195 watts, Neo 2T - 198 watts
9 min 00 sec Type S - 195 watts, Neo 2T - 198 watts
4 min 00 sec Type S - 217 watts, Neo 2T - 220 watts
11 min 30 sec Type S - 217 watts, Neo 2T - 220 watts

The Power2Max Type S reads lower than the Tacx Neo 2T. At 220 watts for the final interval the Type S reads 217 watts compared to the NG Eco reading 225 watts. That would see the NG Eco readings being 8 watts higher than the Type S for the same effort here.

Assuming the Tacx Neo 2T at 220 watts +/-2.2 watts (1% accuracy) baseline is consistent between days (not proven!!! ) both the Type S and NG Eco power meters have a claimed +/- 2% accuracy. 220 watts +/- 4.4 watts (2% accuracy) sees both power meters just about in spec for their claimed accuracy ranges (between 215.6 watts and 224.4 watts), only one reads at the bottom of the range whilst the other reads near the top.









This graph is the final 4 minutes of the interval session using the Power2Max Type S. What's notable if you look at the full graph at the beginning of this post is that the power meter appears to be close to the Tacx Neo 2T under full load but during the recovery sections between intervals with a light load they were further apart. In this graph it shows the final part of the 220 watt interval (Type S - 217 watts, Neo 2T - 220 watts) but then there is a recovery section (Type S - 170 watts, Neo 2T - 176 watts) and then a gentle cooldown (Type S - 79 watts, Neo 2T - 88 watts) where they were even further apart.

In contrast the Power2Max NG Eco in the previous post seems to be more consistent over different intensities, still tracking the Neo 2T readings during the recovery sections.

I'm not too sure why the Power2Max Type S readings are so much smoother and less jumpy than the Power2Max NG Eco readings in the graphs above.


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## Just send it (Feb 20, 2020)

Hey guys,

Saw a few mentions of power meters & pedal strikes possibly causing damage or inaccuracy. Wondering if anyone has personal experience of this happening? 
Interested in getting a new set of cranks with an inbuilt stages power meter, but with rocky/techy local trails pedal strikes are a fairly common experience.

Cheers


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## Brad (May 2, 2004)

Just send it said:


> Hey guys,
> 
> Saw a few mentions of power meters & pedal strikes possibly causing damage or inaccuracy. Wondering if anyone has personal experience of this happening?
> Interested in getting a new set of cranks with an inbuilt stages power meter, but with rocky/techy local trails pedal strikes are a fairly common experience.
> ...


Pedal strikes with power meter pedals are the concern not crank based PM's.
I've been using a Power2Max NG eco for over a year and its been rock solid despite having broken a chain in a rock garden and removed to teeth off the chainring.
Stages is far less vulnerable than other designs and more than adequate for MTBing.

go for it!:thumbsup:


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## Mucker (Feb 14, 2004)

mfa81 said:


> this!! tracking tss is important if you want to keep a training log, also racing is fun to look at number. but a decent 10 or 20m climbing gravel road would be more than enough for most interval workouts!


I just put a power meter on my cross/gravel(4iiii) bike and on my mountain bike(cinch) for this reason.

I was using hrTSS from training peaks to get an idea of how much TSS I was accruing from outdoor rides. I started using intervals.icu and the TSS score that I got from there was significantly different with the training peaks hrTSS significantly lower. I only realized this when I compared my ATL/CTL graphs from last summer. I have a spreadsheet for last summer where I tracked TSS and ATL/CTL but only started using intervals.icu this past winter. My spreadsheet had my maximum CTL at about 63 but intervals.icu showed my max CTL at 79.

Training peaks' hrTSS was vastly underestimating my training load and this was effecting how much I tapered going into races. I usually do better in early season races because most of my training is done indoors on a kickr. But come summer, I was outside most of the time hammering myself into the ground.

I know that comparing power measurements from three different sources is not perfect(indoor kickr, 4iiii, and cinch) but it is giving me a better idea of how much stress I'm accumulating and how much rest I'll need once racing starts. They'll also help me go easy when I need to and go hard when I need to.


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## tgarson (Jul 28, 2015)

I recently had 4iiii do a factory install of a Precision on to my existing crank arm (SRAM X01). I have had power meters on my on-road bikes for almost a decade now but didn’t think it was worth it for my MTB since my primary use case there is just measuring training load as others have stated. Now that 4iiii and Stages have both dropped prices down to $299 I felt it was finally time to get one. 

So far so good and was impressed with the factory install process, though I will say that the data has been pretty surprising so far. I knew my MTB power would be different (spikier) than on my road bike but so far I’m shocked at how different it is.


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## Brad (May 2, 2004)

juan_speeder said:


> For mountain biking?
> 
> I don't recommend one at all. All you'll end up with is less money and random numbers to look at.
> 
> ...


I agree its not a necessity for MTB training. I find I get better results just sticking to HR basedtraining. Fortunately my plan spits out both HR and Watt targets so I can pick whichever. The only benefit to the PM is the TSS score and post ride analysis where i can see where I struggled to maintain watts. I've learned to rather follow the TSS scored and time for the workout rather than the number of intervals as the overload during intervals results in a harder workout than planned.



41ants said:


> I agree for the most part. Most of my training is doing intervals on my road bike or on the trainer... and in that situation I am looking at the numbers. However, I do like it on the mountain bike for tracking tss and looking at post race numbers or when doing my training laps at the local trails. It's neat to go back and look at lap times compared to power.


Agreed I suspect we are in the minority though. I've had to bite my tongue many times when PM evangelists tell me how great it is to train with power on the MTB when their plan is mostly based around HR zones....:rollseyes:



Mucker said:


> I just put a power meter on my cross/gravel(4iiii) bike and on my mountain bike(cinch) for this reason.
> 
> I was using hrTSS from training peaks to get an idea of how much TSS I was accruing from outdoor rides. I started using intervals.icu and the TSS score that I got from there was significantly different with the training peaks hrTSS significantly lower. I only realized this when I compared my ATL/CTL graphs from last summer. I have a spreadsheet for last summer where I tracked TSS and ATL/CTL but only started using intervals.icu this past winter. My spreadsheet had my maximum CTL at about 63 but intervals.icu showed my max CTL at 79.
> 
> ...


I stopped using the training peaks hrTSS and prefer the intervals.icu as their random numbers more closely approximates when I get from the calculations my headuit makes based on the power meters feed. In fact I stopped using TP completely and moved to Today's Plan for analytics and plans



tgarson said:


> I recently had 4iiii do a factory install of a Precision on to my existing crank arm (SRAM X01). I have had power meters on my on-road bikes for almost a decade now but didn't think it was worth it for my MTB since my primary use case there is just measuring training load as others have stated. Now that 4iiii and Stages have both dropped prices down to $299 I felt it was finally time to get one.
> 
> So far so good and was impressed with the factory install process, though I will say that the data has been pretty surprising so far. I knew my MTB power would be different (spikier) than on my road bike but so far I'm shocked at how different it is.


Yeha you're working much harder on the mtb. Your average power should come similar for a similar TSS score between road and MTB though. If not somethings amiss


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## tgarson (Jul 28, 2015)

Brad said:


> Yeha you're working much harder on the mtb. Your average power should come similar for a similar TSS score between road and MTB though. If not somethings amiss


Honestly it was the opposite. I did a longish MTB (3.5 hours) that definitely didn't feel easy and I got a lower TSS than I get on 2 hour road rides. The long MTB ride definitely felt harder and took longer to recover from than the shorter road rides but the TSS says something completely different. I know all about how it's calculated and how avg power, NP, IF, VI, etc all relate to each other.

Maybe that was just an off day or maybe I have a huge L/R imbalance which is causing my L-only PM to report lower. Or maybe I'm just really bad at keeping on consistent power on my MTB and the PM just illuminated the full extent of it. The ride in question was 33 miles of all single track and 4K feet of vert. This particular ride feels a lot harder than other rides I do with more vert because you accumulate a lot of it in shorter steeper pitches over mostly undulating terrain rather than doing any long fire road or other steady smooth surface climbs. What I saw in the data was the spikes I expected for the steep pitches but a lot of low watts as I had to stop pedaling to navigate around technical stuff, ride descents, etc. To be fair it also looks like I was doing a fair bit of coasting after I'd ride a steeper pitch up at VO2 max power. The end result was that both the average and NP were way lower than I would have guessed.

Assuming the data was correct, my conclusion is that I need to do way more VO2 max work in my structured training. I normally would be doing more of that this time of year but reset back to a base block since all of my summer events were cancelled. My base training heavily favors sweet spot intervals which have good overlap with my road power demands, but apparently much less with off road.

I mention all of this because so much of this thread is about 'why do you need MTB power'. Just throwing another example in there to support the argument of it's not all that useful to consult during your ride, but could provide very meaningful insights into your riding in the post ride analysis.


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## WR304 (Jul 9, 2004)

tgarson said:


> Honestly it was the opposite. I did a longish MTB (3.5 hours) that definitely didn't feel easy and I got a lower TSS than I get on 2 hour road rides. The long MTB ride definitely felt harder and took longer to recover from than the shorter road rides but the TSS says something completely different. I know all about how it's calculated and how avg power, NP, IF, VI, etc all relate to each other.
> 
> Maybe that was just an off day or maybe I have a huge L/R imbalance which is causing my L-only PM to report lower. Or maybe I'm just really bad at keeping on consistent power on my MTB and the PM just illuminated the full extent of it. The ride in question was 33 miles of all single track and 4K feet of vert.


With the 4iiii crank arm based power meter you can set a scaling factor in the settings which will affect the power readings (Page 20 of the manual) is that set to default at the moment?

https://4iiii.com/wp-content/uploads/2017/01/4iiii_PRECISION-PRO-USER-MANUAL-20170123-1.pdf

A good test would be to run the new power meter against your other power meters, and then overlay the data to see what the numbers look like when recorded simultaneously. I usually use Microsoft Excel from the original .fit files but the dcrainmaker online analyzer tool is another way of doing this too:

https://www.dcrainmaker.com/analyzer

If you're unsure of the power numbers being correct you could also find a constant gradient climb (tarmac road being best for constant rolling resistance), ride up it and then calculate the estimated power given speed to see if it looks to be in the right sort of area as what the power meter is showing:

https://www.analyticcycling.com/ForcesPower_Page.html

When it comes to offroad power files what I find really useful is to have a calibrated wheel speed sensor on the front wheel of the bike, so that you then have a fairly anchored link between actual speed and the power and cadence data recorded in the file. Relying on GPS speed to go through a file is doable for road riding but trying to make sense of an offroad file based on GPS speed can be tricky! If you have SRAM AXS or Shimano Di2 having the gear shifts written into the file can offer some insights as to how you were riding too.


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## HT-XC (Apr 20, 2020)

Brad said:


> I agree its not a necessity for MTB training. I find I get better results just sticking to HR basedtraining. Fortunately my plan spits out both HR and Watt targets so I can pick whichever. The only benefit to the PM is the TSS score and post ride analysis where i can see where I struggled to maintain watts. I've learned to rather follow the TSS scored and time for the workout rather than the number of intervals as the overload during intervals results in a harder workout than planned.


I disagree with that you don't need a PM for Training. Watts are watts on tarmac or on dirt. Roadcycling might be more steady state based and mtb maybe more v02 oriented. This does change the training method but not how that training stimulus should be measured (imho!). I've personally seen a lot of HR variations on the same course depending on different variables (fatigue-level, coffee, time of day, temperature, fasted or fueled and so on). I don't even know how I would target any interval above endurance that are longer than 5 minutes as my HR lags sometimes up to 45 seconds. If that sort of training works for you then maybe you're more experienced. But to say a PM is not needed for Training (MTB or Road doesn't matter) is something straight out of the 80's.


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## MJW75 (Jul 5, 2018)

I just had a Stage XT M8120 right hand power meter crank delivered today (no clearance for a left hand one on my bike). I'll fit it tonight and report back. I've never had a power meter before though, so my opinion may not mean much.


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## Brad (May 2, 2004)

juan_speeder said:


> For mountain biking?
> 
> I don't recommend one at all. All you'll end up with is less money and random numbers to look at.
> 
> ...





41ants said:


> I agree for the most part. Most of my training is doing intervals on my road bike or on the trainer... and in that situation I am looking at the numbers. However, I do like it on the mountain bike for tracking tss and looking at post race numbers or when doing my training laps at the local trails. It's neat to go back and look at lap times compared to power.





Mucker said:


> I just put a power meter on my cross/gravel(4iiii) bike and on my mountain bike(cinch) for this reason.
> 
> I was using hrTSS from training peaks to get an idea of how much TSS I was accruing from outdoor rides. I started using intervals.icu and the TSS score that I got from there was significantly different with the training peaks hrTSS significantly lower. I only realized this when I compared my ATL/CTL graphs from last summer. I have a spreadsheet for last summer where I tracked TSS and ATL/CTL but only started using intervals.icu this past winter. My spreadsheet had my maximum CTL at about 63 but intervals.icu showed my max CTL at 79.
> 
> ...





tgarson said:


> I recently had 4iiii do a factory install of a Precision on to my existing crank arm (SRAM X01). I have had power meters on my on-road bikes for almost a decade now but didn't think it was worth it for my MTB since my primary use case there is just measuring training load as others have stated. Now that 4iiii and Stages have both dropped prices down to $299 I felt it was finally time to get one.
> 
> So far so good and was impressed with the factory install process, though I will say that the data has been pretty surprising so far. I knew my MTB power would be different (spikier) than on my road bike but so far I'm shocked at how different it is.





tgarson said:


> Honestly it was the opposite. I did a longish MTB (3.5 hours) that definitely didn't feel easy and I got a lower TSS than I get on 2 hour road rides. The long MTB ride definitely felt harder and took longer to recover from than the shorter road rides but the TSS says something completely different. I know all about how it's calculated and how avg power, NP, IF, VI, etc all relate to each other.
> 
> Maybe that was just an off day or maybe I have a huge L/R imbalance which is causing my L-only PM to report lower. Or maybe I'm just really bad at keeping on consistent power on my MTB and the PM just illuminated the full extent of it. The ride in question was 33 miles of all single track and 4K feet of vert. This particular ride feels a lot harder than other rides I do with more vert because you accumulate a lot of it in shorter steeper pitches over mostly undulating terrain rather than doing any long fire road or other steady smooth surface climbs. What I saw in the data was the spikes I expected for the steep pitches but a lot of low watts as I had to stop pedaling to navigate around technical stuff, ride descents, etc. To be fair it also looks like I was doing a fair bit of coasting after I'd ride a steeper pitch up at VO2 max power. The end result was that both the average and NP were way lower than I would have guessed.
> 
> ...


Yes you have to be more selective of your terrain when you're training with a P on the MTB. If you end up with low average and NP its and everything else is working as designed then its likely the amount of coasting.
Have you got your head unit set to ignore zero's? Generally the set up should be to ignore zero's in power and include zero's in cadence. This is ensure that you spend more time pedalling I guess. But if the set up is including zero's then your coasting is pulling your figures down


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## 41ants (Jun 12, 2007)

Yes, I've had problems with 2 stages power meters and I'm now having to replace my race face cinch power meter for the 3rd time. The cinch seems to lose calibration several times during a single ride. Pedaling easy out to a trail during warm-up is not 675 watts . I'll re-calibrate and its good for 10 min. However, currently it only reads cadence, without displaying power. I will say both companies have been easy to deal with in getting a replacement. There's been no explanation to why I've experienced calibration issues on both units, which is fine since they've sent replacements. However, I've reached out Fox/Race Face 2.5 weeks ago... crickets. I'll chalk the slow/no response being covid19 related. Good luck with whatever you go with.


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## beastmaster (Sep 19, 2012)

Stages Sram compatible PMs are out of stock. I ordered one and it said it was available but it wasn't. Oh well. So it goes.

Anyone have experience with the Raceface Cinch Power Meter?


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## Le Duke (Mar 23, 2009)

Has anyone here used a Sigeyi Axo yet? Bunch of different spiders and chainring compatibility. Seems to get good reviews.

https://weightweenies.starbike.com/forum/viewtopic.php?t=159339


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## 41ants (Jun 12, 2007)

Look what just showed up today.. Installing it later this week to use over the weekend.


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## Brad (May 2, 2004)

juan_speeder said:


> For mountain biking?
> 
> I don't recommend one at all. All you'll end up with is less money and random numbers to look at.
> 
> ...





41ants said:


> I agree for the most part. Most of my training is doing intervals on my road bike or on the trainer... and in that situation I am looking at the numbers. However, I do like it on the mountain bike for tracking tss and looking at post race numbers or when doing my training laps at the local trails. It's neat to go back and look at lap times compared to power.





Mucker said:


> I just put a power meter on my cross/gravel(4iiii) bike and on my mountain bike(cinch) for this reason.
> 
> I was using hrTSS from training peaks to get an idea of how much TSS I was accruing from outdoor rides. I started using intervals.icu and the TSS score that I got from there was significantly different with the training peaks hrTSS significantly lower. I only realized this when I compared my ATL/CTL graphs from last summer. I have a spreadsheet for last summer where I tracked TSS and ATL/CTL but only started using intervals.icu this past winter. My spreadsheet had my maximum CTL at about 63 but intervals.icu showed my max CTL at 79.
> 
> ...





tgarson said:


> I recently had 4iiii do a factory install of a Precision on to my existing crank arm (SRAM X01). I have had power meters on my on-road bikes for almost a decade now but didn't think it was worth it for my MTB since my primary use case there is just measuring training load as others have stated. Now that 4iiii and Stages have both dropped prices down to $299 I felt it was finally time to get one.
> 
> So far so good and was impressed with the factory install process, though I will say that the data has been pretty surprising so far. I knew my MTB power would be different (spikier) than on my road bike but so far I'm shocked at how different it is.





beastmaster said:


> Stages Sram compatible PMs are out of stock. I ordered one and it said it was available but it wasn't. Oh well. So it goes.
> 
> Anyone have experience with the Raceface Cinch Power Meter?


basically an expensive branded version of this:
https://teamzwatt.com/products/yding-carbon-mtb-power-meter/


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## TDLover (Sep 14, 2014)

Not just my opinion, but internet consensus seem to be that stages is the worst followed by race face cinch. I would just stay away from those two.


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## Brad (May 2, 2004)

TDLover said:


> Not just my opinion, but internet consensus seem to be that stages is the worst followed by race face cinch. I would just stay away from those two.


Can you share this Internet expert opinion? What exactly are the issues with the Stages and Race Face PM's?


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## 41ants (Jun 12, 2007)

Brad said:


> Can you share this Internet expert opinion? What exactly are the issues with the Stages and Race Face PM's?


I'm not an expert, but I did stay....
There's a reason I burned through 2 stages and 3 race face cinch PM within a 2.5 year period of time. The stages would burn through batteries every 2 weeks, which isn't that big of a deal since I could buy those in bulk. The deal breaker on both of those power meters is they were not able to maintain calibration after performing zero offsets multiple times during a ride. I believe it was a hard pedal strikes, which doomed both of them. I still have the power files I sent to them for review...

Here's a snap shot of the stages. I was feeling good that day, but not that good. Started the day with fresh battery and 0 offset at the start of the ride. Within 5 minutes it started reading abnormally high. 








Similar issues w/cinch.


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## Brad (May 2, 2004)

A single user having a similar problem with two different brand and concept Power meters is not indicative of poor quality products.
I've had a Stage2 DA 9000 on my road bike for 5 years. The Gen 1 was replaced under warranty within 4 months. The Gen 2 replacement has been solid.
I sold the Cinch two years ago because it was not transferanble to my Scapel. It was two yeas old. Zero problems.
My Quarq and Power2max Pm's also zero issues. Does that make these trouble free? Nope. These are electronic components and electronic products sometimes just have issues.

Now the Cinch is quite susceptible to misaligned BB bearing interfaces and run out on the bearings can cause issues. Just like a Powertap hub, if you have bearing issues you're going to get weord readings. Since you have similar issues with high power readings have you had the BB inspected for bearing misalignment?


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## 41ants (Jun 12, 2007)

Yes. Additionally, the issues happened with new bottom bracket installs at the time. 
Also, the stages was on my bmc 4 stroke and the cinch was on my bmc agonist, so two different bikes. My experience is similar to others that I have spoken to in person regarding their stages. My issue now with the cinch is that it doesn't read power at all, only cadence. I currently have 2 quarqs (road & tt bike), both of those have been solid for the past 3 years, but I'm not smashing rocks with either of those bikes


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## tgarson (Jul 28, 2015)

I don't think it's fair to talk about what power meters are the best/worst completely independent of price.

Both Stages and 4iiii now will do left-side only factory installs for $299 USD and have broad compatibility with existing cranks (I think 4iiii's compatibility is better). For most people this is by far the cheapest option vs having to potentially buy a complete new crank or shelling out $1200 to buy SRM's X-power pedals.

Having left-only power is a compromise vs having total power or even better yet, independent L/R. How much of a compromise it is depends on your physiology (how big your imbalance is, how much it may drift under fatigue) and how important it is to you have the most accurate possible data at all time.

Independent of the the single-sided power thing, Stages also had some quality issues in their older units and specifically had a problem with big power spikes caused by an issue with their accelermoter based cadence. I think that's all worked out in the Gen3 unit, and I know that the 4iiii Precision doesn't have that issue.

If I could do it all over again I'd probably shell out and get a Quarq DZero XX1 and know that I have an extremely high quality, accurate and reliable PM. I know my 4iiii Precision is objectively worse than that, but I also paid $700 less than I would have for an XX1 crankset so I'm willing to live with the compromise.


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## Brad (May 2, 2004)

tgarson said:


> I don't think it's fair to talk about what power meters are the best/worst completely independent of price.
> 
> Both Stages and 4iiii now will do left-side only factory installs for $299 USD and have broad compatibility with existing cranks (I think 4iiii's compatibility is better). For most people this is by far the cheapest option vs having to potentially buy a complete new crank or shelling out $1200 to buy SRM's X-power pedals.
> 
> ...


Bingo!
Also for MTB L/R balance is going to be way more variable than on the road because of the nature of the terrain you're riding over. People tend to get lost in the bragging rights that their PM brings. Basically you just want the thing to be able to give you a reasonably accurate TSS, IF, NP and Average Power. YOU'll need to use it in 10s averageing power anyway or the numbers are just all over the place. And considering the abuse It's going to take I don't want to be spending a fortune.
Cinch axle power, Stages power, Rotor2In power, P2M, SRM, Quarq, all these units work. A dud does happen and that needs to be dealt with under the warranty. 
Personally I'd rather put the money into an decent Direct Drive Indoor Trainer but thats just me


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## TDLover (Sep 14, 2014)

Brad said:


> Can you share this Internet expert opinion? What exactly are the issues with the Stages and Race Face PM's?


Are you being oblivious on this matter on purpose?

Stages has had quite the record on problems, have in mind I'm talking about their mtb product line, their road while still having some issues through out their span might be better overall.

The few that come to mind are:

-Waterproof issues (Gen 3 supposedly got this right)
-Battery problems (Not sure gen 3 actually fixed this)
-Connectivity issues: This is a big one and the most important. Most functionality problems from users can be clustered around this one.

The list is long and diverse, most common one seems the stages reading wrong. 41ants wrote the most common problem and I really can't believe you think this is a 1 person issue, there are hundreds of complains in the net about this.

You usually get a power meter to get real accurate numbers, not wrong ones, failing to do that time over time consistently is what makes their mtb power meter so bad. The nickname "random number generator" didn't materialize out of thin air, it is a real thing.

I'm aware of the target market of this power meter (cheap and good enough), but I haven't heard the same complaints about 4iii, for example. I've also gone through two stages for mtb that are just trash at the moment, unusable. Which brings us to the last point, reliability.

-Reliability: I put this one as it seems most everyone agrees given their experience that stages fail sooner than other power meters. It's not uncommon to see comments claiming their SRM, Quark, Powertap or Power2max last years of usage, in excess of 5 or more. In stages case, people don't usually claim that long usage.

I'll give you the benefit of the doubt and ask you: Which mtb powermeter you think is the worst, out of the ones in the current market from "reputable brands"? Don't include Chinese or newly created brands.

As for the race face cinch, that one is relatively new and most of the bad image of it comes from bad reviews. Given how new it is, its almost like stages repeating again, that it makes more sense to stay away from it until they get sorted out.


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## FJSnoozer (Mar 3, 2015)

41ants said:


> Yes, I've had problems with 2 stages power meters and I'm now having to replace my race face cinch power meter for the 3rd time. The cinch seems to lose calibration several times during a single ride. Pedaling easy out to a trail during warm-up is not 675 watts . I'll re-calibrate and its good for 10 min. However, currently it only reads cadence, without displaying power. I will say both companies have been easy to deal with in getting a replacement. There's been no explanation to why I've experienced calibration issues on both units, which is fine since they've sent replacements. However, I've reached out Fox/Race Face 2.5 weeks ago... crickets. I'll chalk the slow/no response being covid19 related. Good luck with whatever you go with.


Just call them, they are super helpful about the cinch on my wife's bike. It has worked for 18 months and now will be warranties for an issue that popped up over night.

About the Cinch:
Had trouble getting data at first. Turned out it was the Garmin Fenix 5s we had. garmin warrantied the watch and the new one connects well. She rarely has any data spikes. Maybe two rides a year, and it's only a split second single power spike. There are a few cadence spikes on many rides, but who cares about that.

I love the water proof housing and the battery life. Our trails are extremely rocky and she would destroy a stages.

It seems accurate based on PE and comparing to trainer rides.

Sent from my iPhone using Tapatalk


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## Brad (May 2, 2004)

TDLover said:


> Are you being oblivious on this matter on purpose?
> 
> Stages has had quite the record on problems, have in mind I'm talking about their mtb product line, their road while still having some issues through out their span might be better overall.
> 
> ...


I'm not being oblivious to anything. I look at actual warranty data of the units that pass through my hands and other colleagues in industry in our region.

Lets cover Stages issues that we've identified between the disributor and the retailers:

When tested, 90% of Stages units in for warranty have no issues at all. Most of the time its a user induced failure

- Incorrect fitting of Shimano cranks arms. Bolt torques are not even and not even in range of 12-15N.m. This issue is especially causal of weird and erratic readings.
- battery replacement out on the trail allows water in past the seal. oro they get water in at this point.
- Pedal strikes that bends the pedal axle creates weird readings or can break part of the PM unit bond to the crank arm. Had one where the arm was slightly bent or the. What a PM was doing on an enduro bike is anyone's guess. But I guess thats Stages fault ...
- A few that have been DOA, 7 in total over 5 years and more than half were Gen1. Gen2 was good and Gen 3 is very consistent.

4iii has a irct to customer business model so I can't comment. Also not many peeps in my area use them but I do like their concept.

Quarq is very popular and we've had a few warranties here too, also mostly user induced. I have one that occasionally cailbrates to a number of 1200 then settles back down to 180-250 within a week. The numbers coming from it are still normal but i've had a few warranty requests for that.

Power2Max isn't too common but the small community using them (Me included) have not had any issues. Its incredibly robust. The entire electronic circuit is potted in resin save for the replaceable 2450 coin battery. I know of one road unit that was DOA random number generator) but again this is a small population in comparison to Stages.

Powertap hubs.... I don't know anyone still using those.

SRM mTB pedals also not trouble free according to DCRainmaker.

So I get it, people have a go at Stages because the man on the internet said he had a problem. As a user, club coach and vendor for quite a few brands of PM I don't see the issues as being due to poor design. Sure others are more robust but they also don't add only 20gr to your bike, more like 200gr.

Being more cost effective also tends to lend itself to more abuse since its cheap so Ill treat it like a cheap unit, whereas a more expensive unit gets babied.

So feel free to continue the personal attacks if it makes you feel like a man. I don't take my data from the internet but from observation of the users around me, the distributors warranty data and their product training around common issues as well as my own trouble shooting.
I don't deal only with Stages but with whatever brand the rider wants to use. My favourite is P2M NG eco but I don't push people away from Stages because its a good product that fits many peoples budgets


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## NordieBoy (Sep 26, 2004)

Brad said:


> Have you got your head unit set to ignore zero's? Generally the set up should be to ignore zero's in power and include zero's in cadence. This is ensure that you spend more time pedalling I guess. But if the set up is including zero's then your coasting is pulling your figures down


I thought it was ignore cadence zeros and include power zeros?
*I don't use power,


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## Brad (May 2, 2004)

NordieBoy said:


> I thought it was ignore cadence zeros and include power zeros?
> *I don't use power,


Yes you're right. Include power zeros and exclude cadence. Thanks for pointing that out. Post dyslexia happens from time to time when it's been a long day


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## WR304 (Jul 9, 2004)

Power2Max have added a new option for the Power2Max NG Eco. When buying the power meter new you can now select to have it hand calibrated at the factory for an extra 100 euros.

That hand calibration is claimed to improve the power meter's accuracy from +/-2% to +/-1%, the same as the more expensive Power2Max NG. I would have chosen that option with mine if it had been available at the time.

https://www.power2max.com/en/2020/0...sed-precision-extended-warranty-now-optional/

Also on the historic announcements there's a bit about the Power2Max NG Eco MTB Shimano version where they recommend it should be used with Wolftooth chainrings and Rotor chainring bolts. I'm sure I remember reading it at the time but that's the actual wording from Power2Max.

https://www.power2max.com/en/2019/07/p2m-tech-news-power2max-und-shimano-mtb/

.


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## bloodninja (Jul 11, 2012)

I haven't seen any reviews or user reports on the SRM X-Power yet. Anyone else?


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## litany (Nov 25, 2009)

bloodninja said:


> I haven't seen any reviews or user reports on the SRM X-Power yet. Anyone else?


Not out yet?


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## bootsie_cat (Nov 3, 2004)

Not out yet. But they are making a powermeter chassis that fits on an XTR or XT crankset. Pretty reasonable and works great.



bloodninja said:


> I haven't seen any reviews or user reports on the SRM X-Power yet. Anyone else?


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## cal_len1 (Nov 18, 2017)

DCRainmaker has a set, but my guess is since they aren't officially out, he hasn't dropped the review yet. Look for that in the future.


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## bloodninja (Jul 11, 2012)

bootsie_cat said:


> Not out yet. But they are making a powermeter chassis that fits on an XTR or XT crankset. Pretty reasonable and works great.


Oh, that's weird. I got an email from SRM on 4/17 that said that the first batch was available for purchase on 4/20.


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## MJW75 (Jul 5, 2018)

I have my Stages Shimano XT M8120 right hand crank fitted now. I've done a few rides on it and it seems good, but this is my first powermeter, so I can't really comment beyond that.

I will however say that Stages do not do the M8100 right hand cranks. Note that all the left hand crank arms are the same, so fit M8100, M8120 and M8130. I originally had M8100. The difference is the Q Factor and ring offset. The M8120 Q Factor is +6mm over the M8100. The issue was that they only provided one 3mm spacer, so I needed to buy another.

I pointed this issue out to them and they replied saying the other spacer comes with the left hand crank. This makes no sense. Anyone buying the left hand crank will already have the required spacers. So be aware if ordering a right hand arm with increased Q Factor, you will need an extra spacer! Shimano do sell the spacers separately and they are only £5.


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## WR304 (Jul 9, 2004)

I finally got round to finishing off the spreadsheet to write this post. It's taken me a while.

Back in May I had a Specialized Turbo Levo SL comp carbon ebike to ride for a week as a demo whilst my Orbea Oiz was awaiting repairs.

The Specialized Turbo Levo SL is a low power ebike with only a 250 watt maximum pedal assist and a small 320wh battery. This was a stock bike so weighed around 42lbs, heavy for a normal bike but light for an ebike.









What makes this bike worth talking about here is that its Mahle motor has torque sensors built in and it broadcasts this information via ANT+ so can be connected to a Wahoo or Garmin bike computer. The bike will then transmit rider power output, cadence and speed data as though it has an integrated power meter that is saved into the .fit file. It has a built in power meter.









It also pedals quite well with the motor off so I was really interested to see if the power data would be good enough to use it as a training tool. With a Wahoo Elemnt Bolt it saves how much time is spent in each motor mode within the .fit file. The bike has a very limited battery life and eats battery life climbing so a lot of the time is spent with the motor off to conserve that battery.

So is the Specialized Levo SL power data any good and a replacement for a standalone power meter? In short no, although the cadence data transmitted by the bike seems ok the power meter data was all over the place being both inaccurate and inconsistent.









This picture shows a small extract of a climb that I frequently do hill repeats on and know very well on the Specialized Levo SL ebike. You can see from the green cadence and blue speed traces that this was a constant effort and I was doing around 250 watts with the motor off so rider power only. The solid yellow line shows where my actual power output would be whilst the thin yellow line is the power output recorded from the Levo SL. What's notable about the power line from the Levo SL is that it's not going up and down. It's going up, going down and then staying down for an extended period of time so isn't consistent. When I recorded this ride I was watching the Wahoo screen very carefully trying to gauge my pace against the display but that pattern of up and staying down had no relation to what I was doing in terms of pedalling.









For comparison this is the small extract of climb ridden on my Orbea Oiz and recorded on a Power2Max NG Eco power meter. I was doing around 250 watts but now you can see how the thin yellow line of the power meter recording is tracking far more closely to the solid yellow line. That's what the Specialized Levo SL power trace should look like too!









I also put the Specialized Levo SL on the Tacx Neo 2T turbo trainer and did the same erg mode workout as shown previously for my Power2Max NG Eco and Power2Max Type S power meters. This was with the motor off throughout and no back wheel. With no back wheel there is no speed sensor input so the Specialized Levo SL turned itself off partway through the turbo trainer workout, which is why there is a drop with no data.

As with the other power meters the closer the Levo SL readings are to the Tacx Neo 2T power readings the better. In this test the Specialized Levo SL was way off, consistently reading high by a large margin. For the final 220 watt interval the Levo SL averaged 260 watts, 40 more than the Taxc Neo 2T! It's also notable just how unstable the Levo SL readings are. The readings were swinging up and down by as much as 150 watts second to second.

I also did a 40 minute virtual FulGaz ride on the Tacx Neo 2T riding the bike normally with gears (not pictured) including some sprints and comparing the readings and that was all over the place. The overall average power was 128 watts for the Tacx Neo 2T compared to 159 watts for the Levo SL and the sprints were 100 watts higher on the Levo SL than the Tacx Neo 2T.


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## tgoods (Jan 22, 2018)

Just installed a power2max NGeco on my SRAM dub crank. So far so good on 3 rides. Came in at $590 from Power Meter City, which included a RaceFace ring and Wolftooth bolts. Hoping to get 2-3 years out of this Power Meter.


Sent from my iPhone using Tapatalk


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## Salespunk (Sep 15, 2005)

Some really good data in here. A few questions for the group;

1) How to you correct for the variance in power meters on road vs mountain? I have Quarq setups for both and the FTP along with each segment (1 minute, 5 minute, 20 minute, etc) are significantly different on the road vs mountain. It would be much more useful to see power by bike rather than having all the data blended together like it does on Strava.

2) I am on my second Quarq MTB setup and it is the second one I have bent. Both times I have kicked a rock off my front wheel and had it strike the battery holder bending it out towards the pedal. Second one has not seemed to affect the accuracy yet though. Anyone else have a similar issue or do I just have wildly bad luck.


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## litany (Nov 25, 2009)

Salespunk said:


> Some really good data in here. A few questions for the group;
> 
> 1) How to you correct for the variance in power meters on road vs mountain? I have Quarq setups for both and the FTP along with each segment (1 minute, 5 minute, 20 minute, etc) are significantly different on the road vs mountain. It would be much more useful to see power by bike rather than having all the data blended together like it does on Strava.
> 
> 2) I am on my second Quarq MTB setup and it is the second one I have bent. Both times I have kicked a rock off my front wheel and had it strike the battery holder bending it out towards the pedal. Second one has not seemed to affect the accuracy yet though. Anyone else have a similar issue or do I just have wildly bad luck.


If you have, or know someone with a pedal based power meter, or an accurate trainer, you could do a couple rides and see how they differ. Pain in the butt for sure though.

I have been using MTB quarqs since 2012 and never had such an issue. Hitting the battery cover... I mean that just sounds like one in a million. You must be extra lucky. It's pretty small and doesn't poke out much...


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## WR304 (Jul 9, 2004)

bloodninja said:


> I haven't seen any reviews or user reports on the SRM X-Power yet. Anyone else?


There was an article today on Bikeradar (Friday 24 July 2020) that they had just received a set of SRM X-Power pedals for review:

https://www.bikeradar.com/features/first-look-friday/fenwicks-professional-chain-lube/

.


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## WR304 (Jul 9, 2004)

Salespunk said:


> Some really good data in here. A few questions for the group;
> 
> 1) How to you correct for the variance in power meters on road vs mountain? I have Quarq setups for both and the FTP along with each segment (1 minute, 5 minute, 20 minute, etc) are significantly different on the road vs mountain. It would be much more useful to see power by bike rather than having all the data blended together like it does on Strava.
> 
> 2) I am on my second Quarq MTB setup and it is the second one I have bent. Both times I have kicked a rock off my front wheel and had it strike the battery holder bending it out towards the pedal. Second one has not seemed to affect the accuracy yet though. Anyone else have a similar issue or do I just have wildly bad luck.


*Splitting Ride Types In Reports*
In Strava although you can mark different types of ride and equipment (mountain bike, road bike, ebike etc) you can't filter your power data by these categories. The bad power data from the Specialized Turbo Levo SL rides I did (even though it is marked as ebike) still shows up in my overall 2020 Strava power curve data. There's not much to be done within Strava unfortunately.

In WKO4 (I bought a WKO5 licence when it came out but still haven't got round to switching) it is possible to flag a ride as either a mountain bike or road bike ride. This flag allows the overall reports to be either filtered individually or merged together, so that only the power numbers from one type of ride are included. The way I use this is to split out my turbo trainer rides and my outdoor rides.

If you look at this summary there are four indoor rides and three outdoor rides for the week so far. The indoor rides are marked with the tyre symbol whilst the outdoor rides are marked with the chain link symbol.









In this summary report I have filtered the week so that only the three outdoor rides are included in the summary. This includes any other reports run such as totals, mean maximal power curve etc.









*The Two Power Meters*
In theory if you have two Quarq power meters they should both give close to the same readings within their quoted accuracy range of +/-1.5%. It shouldn't matter that one is a mountain bike model and one is a road bike model. If your mountain bike power meter has been damaged by a rock that could potentially be an issue though.

If the power curves are very different I'd try and work out whether this is because of the terrain you're riding (offroad vs road riding can see different patterns in the power data due to how it's ridden) or if it's down to the power meters.

The place to start for a rough comparison between the two power meters would be to go and do a tarmac road loop on the mountain bike, and then the same loop on the road bike back to back on the same day. Pace yourself on heart rate or perceived exertion, so you do roughly the same effort each time ignoring the power readings, and then have a look at the power outputs and power curve for some of the Strava segments when you get back. The speed will be different between the two bikes but it will give an idea of if the power meters are significantly different when used on the same route.

If you include a constant gradient climb (tarmac road being best for constant rolling resistance), ride up on it on both bikes and then calculate the estimated power given speed to see if it looks to be in the right sort of area as what each power meter is showing:

https://www.analyticcycling.com/ForcesPower_Page.html

A good test if you have one available would be to try both power meters on a turbo trainer such as a Tacx Neo 2T for the same workout, and then overlay the data to see what the numbers look like when recorded simultaneously. I usually use Microsoft Excel from the original .fit files but the dcrainmaker online analyzer tool is another way of doing this too:

https://www.dcrainmaker.com/analyzer

According to the SRAM website if you have a Quarq XX1 power meter (not XX1 Eagle) if you change chainring size it may need recalibrating afterwards:

https://quarq.zendesk.com/hc/en-us/articles/217034068-Factory-Calibration-Needs

It doesn't seem to be possible to recalibrate the slope on a Quarq at home. If one of them is clearly showing bad readings it would need to be sent back to Quarq to be repaired.


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## Vin829 (Mar 29, 2019)

I’ve also just put on the Power2max power meter on my XC bike. So far very happy with it. Also the torque sensor on my Levo SL is a great training tool when I ride that bike for recovery rides


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## Daniel Thomas (Aug 1, 2015)

How much fluctuation in power readings do you guys consider normal? I have very little experience in the use of power meters. I have a Stages L on my Oiz. I am currently rebuilding after a patella fracture and I wanted to use the last flat kilometers of a ride to do a constant effort interval just to see where I am at. I kept an eye on the power readings as I rode and observed a lot of fluctuations. I am talking about +/- 30W from one second to the other. I was concerned that there is water damage because earlier on the ride the crank got submerged for a few seconds (oops ). According to the specs, it can handle that. Back home, I opened the battery cover and didn't see any signs of water ingress. Nevertheless, I took it inside, cover open, for a day to dry just in case and put in a new battery.

I have now done a test ride on the flattest and smoothest stretch of road nearby. I rode it both ways, each direction without changing gear and pedaling as constant as I could manage. Both cadence and speed are pretty constant. The power, however, is not. Now I am wondering if there is something wrong or if this is normal for the minimal level of smoothing? I see some graphs in the thread that point towards the later.

I am recording the data with the Wahoo on my phone, which connects to the power meter using bluetooth. I don't know what kind of smoothing is applied in the Wahoo app. I also looked at the power in the Stages app directly and my impression is that the number jump around even more than in the Wahoo app.


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## dcb (Sep 19, 2005)

Daniel Thomas said:


> How much fluctuation in power readings do you guys consider normal? I have very little experience in the use of power meters. I have a Stages L on my Oiz. I am currently rebuilding after a patella fracture and I wanted to use the last flat kilometers of a ride to do a constant effort interval just to see where I am at. I kept an eye on the power readings as I rode and observed a lot of fluctuations. I am talking about +/- 30W from one second to the other. I was concerned that there is water damage because earlier on the ride the crank got submerged for a few seconds (oops ). According to the specs, it can handle that. Back home, I opened the battery cover and didn't see any signs of water ingress. Nevertheless, I took it inside, cover open, for a day to dry just in case and put in a new battery.
> 
> I have now done a test ride on the flattest and smoothest stretch of road nearby. I rode it both ways, each direction without changing gear and pedaling as constant as I could manage. Both cadence and speed are pretty constant. The power, however, is not. Now I am wondering if there is something wrong or if this is normal for the minimal level of smoothing? I see some graphs in the thread that point towards the later.
> 
> I am recording the data with the Wahoo on my phone, which connects to the power meter using bluetooth. I don't know what kind of smoothing is applied in the Wahoo app. I also looked at the power in the Stages app directly and my impression is that the number jump around even more than in the Wahoo app.


I've been riding with power meters for about 10 years on road, cross and mtb bikes so I've looked at a fair number of files. I don't think your graph looks out of the ordinary and one thing I'd recommend is switching your computer to displaying a 3 second rolling average if you're looking at it while you ride.

On my mtb the power data is for use in post ride analysis. I can't look at it while I'm on the trail except maybe on some longer smoother uphill sections. If you do more riding on the road while trying to keep a smooth cadence you may find that your power application becomes a bit less jumpy but I'm not sure there's much benefit in putting any time into that.


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## Daniel Thomas (Aug 1, 2015)

Ok, thank you! I haven't seen any way to control smoothing in the Wahoo app. I think I will be getting a Garmin Edge 1030, which seems to have such options.

On the bike trails, there is so much variation in the ground conditions for most of the time that momentary power is probably not useful at all. I learned smooth pedaling on the fatbike because if you hit the pedal to abruptly, the big wheels tend to bounce a lot. Regular wheels don't, so I don't care about such things and just ride  
I also absolutely believe the science that says that there is no benefit to mess with one's natural cadence.


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## dcb (Sep 19, 2005)

I missed the part about the Wahoo app instead of a computer. Yeah a Garmin will be able to give you 3, 10, 30 second rolling averages, lap power etc. I've got an older 510 and it does all of that.


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## Daniel Thomas (Aug 1, 2015)

I don't even know what model of Garmin I have got. It is ancient. Looks like a late 90's Nokia phone. I have used it for a 5 day bikepacking trip and only need to change the AA batteries once. Not bad, but when I wanted to update a track from my cell phone I couldn't because nobody at the camp site had the old type of USB cable and I didn't bring one. It will be nicer with a modern one. This is also my strategy for getting approval  my partner loves bikepacking and it doesn't hurt when she is happy with money spent on bike stuff. :lol:


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## WR304 (Jul 9, 2004)

Daniel Thomas said:


> How much fluctuation in power readings do you guys consider normal? I have very little experience in the use of power meters. I have a Stages L on my Oiz. I am currently rebuilding after a patella fracture and I wanted to use the last flat kilometers of a ride to do a constant effort interval just to see where I am at. I kept an eye on the power readings as I rode and observed a lot of fluctuations. I am talking about +/- 30W from one second to the other. I was concerned that there is water damage because earlier on the ride the crank got submerged for a few seconds (oops ). According to the specs, it can handle that. Back home, I opened the battery cover and didn't see any signs of water ingress. Nevertheless, I took it inside, cover open, for a day to dry just in case and put in a new battery.
> 
> I have now done a test ride on the flattest and smoothest stretch of road nearby. I rode it both ways, each direction without changing gear and pedaling as constant as I could manage. Both cadence and speed are pretty constant. The power, however, is not. Now I am wondering if there is something wrong or if this is normal for the minimal level of smoothing? I see some graphs in the thread that point towards the later.
> 
> I am recording the data with the Wahoo on my phone, which connects to the power meter using bluetooth. I don't know what kind of smoothing is applied in the Wahoo app. I also looked at the power in the Stages app directly and my impression is that the number jump around even more than in the Wahoo app.


That graph looks like the power meter is working normally. It's normal for the onscreen readings, and the recorded readings saved into a .fit file, to be quite jumpy with differences in power from second to second.









When you pedal the force applied through the pedal stroke isn't a circle. It has peaks and troughs that oscillate through the pedal stroke. A typical cadence of 90rpm say would see 1.5 pedal strokes per second and frequent changes in power within that second.

The limitation is that although ANT+ can transmit and receive up to 4 data points per second and bluetooth can transmit up to 64 data points per second apparently to enable this drains battery life too fast so head units and displays end up only refreshing once per second which isn't really enough.

_"According to Quarq founder, Jim Meyer, recording every second is the way to go. Under that protocol, the head unit essentially falls asleep between signal transmissions, wakes up once per second to grab the most recent power value, and then falls back asleep to wait for the next one. Just taking a wild guess, it might be 'awake' for 0.1 seconds to grab the data, and then fall asleep for the next 0.9 seconds. This means that it is only grabbing 1/4th of the potential data - one of the four data packets. Smart Recording goes further and will repeat power values in your file if it does not detect a change, to save battery and memory capacity (but losing further accuracy)."_ *Slowtwitch*

https://www.slowtwitch.com/Tech/Power_Meter_101_3643.html

This one second limitation, for a constantly changing power output within each second, can see 1 "and a bit" pedal stroke in one second, followed by 1 "and a bit" pedal strokes in the next second and so on. Those "and a bit" partial pedal strokes can be from different parts of the pedal stroke (high or low power) so the recorded power output in a .fit file will fluctuate from second to second, even for a constant effort. Each second of recording could have different parts of the pedal stroke in.

The power smoothing options for head units (3, 5 ,10 second smoothing etc) don't change the actual recording frequency of the data by the head unit. For a current Garmin or Wahoo head unit it will still record power data at 1 second intervals regardless of the power smoothing option chosen. What they do is apply a rolling average to try and reduce the jumpiness of the second by second onscreen power data to make it a little easier to pace to when riding.

Analysis software post ride such as Golden Cheetah, WKO5 etc does the same thing. It doesn't change the actual recorded data but displays it as a rolling average to make it easier to interpret. Websites such as Strava apply some smoothing to their analysis graphs too.

With the Stages phone app there's supposed to be a high speed recording mode that you can enable that will send you a .csv file of the power data to look at for more detail in Excel post ride also.

https://www.dcrainmaker.com/2013/09/cycling-metrics-streaming.html

.


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## Placibo (Jan 20, 2013)

I recently installed a power2max ngeco on my Slx 7100. I enjoy looking at the data and using the tss to help log my training. It is super simple to install and set up and extremely easy to use.


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## Daniel Thomas (Aug 1, 2015)

WR304 said:


> The limitation is that although ANT+ can transmit and receive up to 4 data points per second and bluetooth can transmit up to 64 data points per second apparently to enable this drains battery life too fast so head units and displays end up only refreshing once per second which isn't really enough.
> .


Thanks, much appreciated!

I didn't know the transmission rates were that low. However, I think a distinction must be made between sampling rate, transmission rate and recording rate. I don't think it makes any sense for a power meter to take a sample only four times per second, let alone once. It has to take more samples than that, otherwise it would not be possible to determine cadence. There is a theorem that says that the sampling frequency must be greater than two times the highest frequency that has to be resolved. It's called Nyquist-Shannon sampling theorem. It means for example that in order to be able to measure a cadence of 90, you must take more than 180 samples per minute, or 3 Hz. If the power meter takes only 4 samples per second, it would only be able to measure cadence correctly when it less than 120. Also, if the sampling frequency is equal to the cadence, the measurement would always be taken at the same crank angle, i.e. the cadence would appear to be zero.
For these reasons, I would expect the power meter to take many samples per second, process the data and then transmit a processed result. But if this level of fluctuation is normal, then they apparently don't.


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## Lone Rager (Dec 13, 2013)

There are some fallacies in your logic, but your last sentence is correct. The PM transmits processed results, not raw data.


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## WR304 (Jul 9, 2004)

Daniel Thomas said:


> Thanks, much appreciated!
> 
> I didn't know the transmission rates were that low. However, I think a distinction must be made between sampling rate, transmission rate and recording rate. I don't think it makes any sense for a power meter to take a sample only four times per second, let alone once. It has to take more samples than that, otherwise it would not be possible to determine cadence. There is a theorem that says that the sampling frequency must be greater than two times the highest frequency that has to be resolved. It's called Nyquist-Shannon sampling theorem. It means for example that in order to be able to measure a cadence of 90, you must take more than 180 samples per minute, or 3 Hz. If the power meter takes only 4 samples per second, it would only be able to measure cadence correctly when it less than 120. Also, if the sampling frequency is equal to the cadence, the measurement would always be taken at the same crank angle, i.e. the cadence would appear to be zero.
> For these reasons, I would expect the power meter to take many samples per second, process the data and then transmit a processed result. But if this level of fluctuation is normal, then they apparently don't.


Although the transmission rate to the head unit is low modern power meters have a much higher internal sampling rate so the hardware is capable of more detail. The power meter takes this higher frequency raw data, processes and filters it internally in software before transmitting it on. Apparently a Quarq power meter for example has an internal data rate of over 5,000hz (5,000 samples per second).

https://www.bikeradar.com/reviews/training/power-meters/quarq-elsa-10r-power-meter-review/

An example of where this higher data rate is actually used for displayed data would be the Wattbike indoor bike which has a 100hz (100 samples per second) data rate that it uses for its measurements. That indoor bike has its own hard wired head unit as a display so uses that higher data rate (skipping the transmission limitations of ANT+ or Bluetooth) for its pedalling analysis features as shown in this video:











https://support.wattbike.com/hc/en-gb/articles/115001848609-A-Beginner-s-Guide-To-Perfect-Pedalling

https://support.wattbike.com/hc/en-gb/articles/115004557789-Pedalling-Effectiveness-Score-PES-

With a bicycle power meter outdoors there are more inputs to take into account than just pedalling forces. A big part of the internal software filtering is to determine what forces to include as pedalling and what to exclude. This software filtering is the "secret sauce" that lets the power meter produce meaningful data at all. It varies between power meters too which helps explain some of their characteristics. If you imagine pedalling over some cobble stones for example with your Stages crank, or riding down a rough descent freewheeling with the bike bouncing around, that's putting non pedalling force inputs, ofter very strong non pedalling force inputs, into the crank arm. If these aren't filtered out then they appear in the power data as power spikes.

When you see references to 2,000 watt power spikes it's often where one of these non pedalling inputs has got through the filtering in error. If there's too much filtering then the power meter could be excluding valid pedalling inputs but if there's too little the power meter will include non pedalling inputs making the data it produces inaccurate. With Stages for example they've released several firmware updates over the years tweaking the filtering of their power meters.

How power meters filter and process the data varies between brands so they aren't all the same. Here's a comparison of the data from 3 different power meters showing how different they can be. In these graphs the yellow line shows my power output for a 30 second extract of a ride (not the same ride unfortunately! ) with the Graph Y axis for Power set to the same scale each time and no smoothing applied.









This graph is from my Tacx Neo 2T turbo trainer doing a FulGaz virtual ride indoors (not erg mode). The Tacx Neo 2T produces really smooth data without second to second up and down jumps. The yellow line is almost a smooth curve and it's super easy to pace with when riding as a result. It's highly processed.









This graph is from my Power2Max NG Eco power meter riding uphill outdoors. This power meter has much more jumpy data with frequently 40 to 50 watt differences in readings every second. This is a lot like what you're seeing with the Stages power meter.









This graph is from my Powertap MTB hub riding uphill outdoors. This was from a ride recorded back in 2010. This old Powertap had by far the jumpiest data with jumps in power of more than 100 watts second to second.


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## Lone Rager (Dec 13, 2013)

Haven't read the previous post in detail, but FWIW, I'll mention that hub based PMs (e.g. Powertap) don't rotate synchronously with the crank as do crank and pedal based PMs so data acquisition and smoothing can be different.


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## Daniel Thomas (Aug 1, 2015)

So you are saying my peak power is not really 2300 W? What's next, are you gonna say that I didn't really hit 120 kph descending? That's it, I'm out!

Thanks for clearing that up, WR304! I'll be getting a good bike computer and keep going!


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## NordieBoy (Sep 26, 2004)

I've finally got a power meter on the way 

It's for the road bike, but it's a start.
Unused Shimano 105 4iiii Precision for $95us off a local auction site.

Just in time for the last race of the year.
Oops, that was on Tuesday...

Oh well, just in time for next year's racing...

I don't usually train on the road bike as there's no decent hills within 15km.
A lot of short hills, so I may just get into the swing of hill reps.

May even try it on the gravel bike if it clears the chain-stay.


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## NordieBoy (Sep 26, 2004)

Woohoo!


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## NordieBoy (Sep 26, 2004)

Just scored another slightly used 4iiii XT one for the MTB!
Was 3x as much, but averages out to a really good price still 

Won't be able to test it for 3 days though


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## DrewBird (Apr 11, 2007)

If anyone is looking for a P2M NG-Eco for Shimano direct mount, I have a lightly used one in great condition. PM me if interested.


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