# Why use Cadence and Speed Sensors on a Mountain Bike?



## L84Beer (Jun 24, 2015)

I currently use a HRM and my iPhone as a GPS device and track my rides using Cyclemeter and just started uploading to Strava. I like analysing my rides, comparing them to others who are stronger and faster, as I look to lose weight and improve my fitness. I am trying to figure if dedicated speed and/or cadence sensors would provide me with useful data as I analyze my rides and look for areas to improve.

I can see the benefit of these sensors on a road bike, where routes, conditions (except for weather) and user input would tend to be more uniform. However, on a mountain bike I would think the variability of trail conditions and the high intensity intervals of constant undulations would make the data harder and perhaps less useful to analyze. I recognize that canopy cover will greatly skew my gps speed readings, but time is a very reasonable substitute between points.....

This said, how do folks use the data from cadence and speed sensors on their mountain bike rides in undulating and tree covered environments?


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## blkangel (Aug 8, 2014)

I don't. Like you said only use cadence (don't need speed because GPS takes care of speed) on my road bike. I use the speed sensor on my stationary trainer.


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## Harold (Dec 23, 2003)

A cadence sensor on a mtb is of limited utility, unless you want to be sure you're keeping your cadence where you need it on long climbs. Otherwise, your cadence will be all over the place on mtb.

As for why to use a speed sensor - it's not for speed. This is why.

We did the same ride. My wife was a little slower, but did the same distance I did.

Mine:
https://connect.garmin.com/modern/activity/1221931458

Hers:
https://connect.garmin.com/modern/activity/1222073261

I use a wheel sensor, and she does not. I have both on my road bike. For this ride, I recorded 21.38 mi. She recorded 20.17 mi, a difference of 1.21 mi. Her track was over 5% shorter than mine, yet we rode the same distance. That shorting of distance is inherent in GPS-only distance measurements. On a twisty mtb trail, you're going to lose a fair bit of distance over the course of a full ride. If you don't care about that, then that's one thing. But a wheel sensor on the mtb is ABSOLUTELY ESSENTIAL if you want to keep track of accurate distances (it will also affect recorded speeds, too).

For me, there are 3 things I care about with my recorded GPS data. 1. The place. I just want a reasonably accurate GPS track for storytelling and memory purposes. 2. Time. I want to know how long I've been riding. It helps me meter food consumption. If I have to finish at a certain time, I know I need to limit my ride time, etc. 3. Distance. I like to keep a tally of how far I ride in a year. Accurate distances are important for this.


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## blkangel (Aug 8, 2014)

That is great info. Did not even think about the accuracy issue with GPS over winding road. Hum.

I too keep track of every mile I ride. I gave yearly goals and that keeps me motivated. I have lost miles, not thrilled about that.


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## cyclism00 (Nov 25, 2014)

It's not even just the winding roads, if you ride in areas with tree canopies, you will lose signal at times. I think a speed sensor is essential for those reasons.


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## Harold (Dec 23, 2003)

cyclism00 said:


> It's not even just the winding roads, if you ride in areas with tree canopies, you will lose signal at times. I think a speed sensor is essential for those reasons.


Loss of signal isn't that big of a deal anymore, honestly. I remember using GPS in the early days of consumer GPS in the late 90's and early 2000's and yeah, signal loss was a major issue. But that has steadily improved over the years to the point that I simply don't lose a signal anymore on my rides. I might have a couple days per year if I'm unfortunate where the GPS signal is poor and tracking is just terrible. But I still have a signal. And yes, the wheel sensor ensures that I will not lose out on the mileage tally from that ride. I now have a device with GPS + GLONASS satellite reception, so the likelihood of those days has probably dropped pretty significantly.


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## RS VR6 (Mar 29, 2007)

I have a GSC-10 on my road bike and just use the 520 by itself on the MTB's. Accuracy isn't a super big deal for me. As long as my mileage is in the ballpark...I'm ok with it.


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## Oh My Sack! (Aug 21, 2006)

I have the 520 with HRM, Cad, Spd sensors on both my road and mtb. I bought the Cad and Spd sensor exclusively for the road bike but a week later, my buddy shows up with a new Cad and Spd sensor that came on a bike he had just repurchased from a Garmin sponsored road rider. He didn't want them so he kicked them down to me so on the MTB they went. Like Harold already mentioned, I like the speed sensor for the reasons he has already pointed out. It's just more accurate data. I enjoy the cadence sensor as I periodically watch where I'm at when climbing on the less chunky and more XC flow trails with longer runs. That said, I don't think I'd bother to go buy one for the mtb, though.


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## ghettocruiser (Jun 21, 2008)

It provided evidence of what I climbed and what I had to walk, for future reference (and/or Strava cred). Even if I was ratcheting the cranks on really steep technical stuff, it still was obvious (to me at least) in the cadence replay when I was on the bike and when I was off. 

If you live primarily for the downhills, this will be of absolutely no use to you.

Another Random use: When I saw something along the trail I wanted to mark the location of, like a tree about to come down or a wash-out in progress, I would flutter the left crank arm magnet over the sensor a few times to create a cadence spike that marks the spot. Hands free. This probably won't work with the new magnet-less sensor, another reason for me NOT to upgrade.


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## NordieBoy (Sep 26, 2004)

ghettocruiser said:


> Another Random use: When I saw something along the trail I wanted to mark the location of, like a tree about to come down or a wash-out in progress, I would flutter the left crank arm magnet over the sensor a few times to create a cadence spike that marks the spot. Hands free. This probably won't work with the new magnet-less sensor, another reason for me NOT to upgrade.


That is cool.


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