# Davichi Tandem



## Circusjunk (Aug 20, 2004)

I was doing 24 hours of Pats Peak this past weekend , and this couple was racing oan a davinch Tandem, and what was so unusal ( andI wish i got a good pictur of it ) was they were not connected in the typical fashion , they both has chains thet went to a 3rd Bottom Bracket that actually feed to the other side and teh Chainrings , and they told me they could both coast independetly of the other. was quite interesting.

any one else seen or herd about this set up ?


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## Speedub.Nate (Dec 31, 2003)

Subscribe to DFL's recent thread to follow the progress on a very special frame he's building, which will include da Vinci's "Independent Coasting" system.

http://forums.mtbr.com/showthread.php?t=410868

I don't know nuttin' about it other than what I've read. Sounds interesting, but I've heard hit and miss reviews for off-road riding.

Here's their website: http://www.davincitandems.com/


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## TandemNut (Mar 12, 2004)

We had a daVinci in our test fleet for a while. It's out for repairs just now. The independent pedaling offers some advantages for some tandem teams. As with anything tandem, there is also a trade-off. Here's some pricing information on the frames.
http://mtbtandems.com/daVinciframe.html


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## Speedub.Nate (Dec 31, 2003)

BigNut said:


> We had a daVinci in our test fleet for a while.


So Alex, tell me something... my understanding is the system is not a differential per se, it's more like a clutch. Either can coast, but if both are pedaling, they must be producing equal effort / RPMs to contribute, otherwise the slower pedaling rider is more-or-less coasting?

Is this system a disadvantage for mismatched teams?


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## itsdoable (Jan 6, 2004)

The DaVinci jack shaft carries 2 freewheels, one for the stoker and one for the captain. Front dérailleur is on the jack shaft. 

If the captain and stoker have different cadences, you can set up the freewheel/chainrings with different ratios. However, mismatched teams usually have similar cadences, just different power output. You don't need "equal effort" to get contribution from both riders on any tandem.


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## TandemNut (Mar 12, 2004)

itsdoable said:


> If the captain and stoker have different cadences, you can set up the freewheel/chainrings with different ratios. However, mismatched teams usually have similar cadences, just different power output. You don't need "equal effort" to get contribution from both riders on any tandem.


Agree that you don't need equal effort or strength to get contribution from both riders. That very statement captures what is so cool about tandems; they're great equalizers. 
However, there are some differences between the IP system and a conventional system with respect to the particular issue that was raised:
On a conventional tandem, the timing chain from the stronger rider helps pull the cranks of the less-strong rider, since they're chained together with the timing chain. Or, in another example, two riders of equal strength may have said strength at different points of the stroke, and again, the stronger rider at that point in the stroke is pulling the weaker rider's cranks through that portion of the stroke. 
On a da Vinci, there's no chain keeping the two riders syncronized, and therefore, no chain taking power from the stronger rider through the timing chain and "pulling" the weaker rider or weaker stroke section. The stronger rider is relieving some of the effort from the weaker rider/stroke by lessening the resistance, but he is not actually pulling the weaker rider's cranks with his cranks. 
Now, how much real-world difference actually is there would be a question for the engineers in the audience. But we noticed that difference on our da Vinci.
A semi-independent system would bridge the gap between the two.


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## arly (Apr 20, 2005)

*daVa what?*

Gee has someone ever seen or used this system?? :eekster: Seriously we've been using DaVinci IP bikes for years and can't say enough good things about it,, especially for off-road applications. As stated by others you have to be pushing in order to engage your own free-wheel but the real advantage is when going over logs either rider can hesitate to keep their own crank from striking it. Or when riding on tight single track as we commonly do, ether rider can keep their own pedals from striking logs, rocks, going over humps of earth or whatever obstacles that are found along the trail. Plus while riding uphill and someone unclips, the other person can continue to move the bike along while the other is reclipping in. In all the situations just mentioned, independence of your pedals makes riding trails lots easier, or in some case possible at all.. Another advantage is having wider range of gears, lowest being a sub 20in gear, yet the largest is so big we can still be pedaling while going over 40mph! Hope that answers a few of your questions. We should add that we have lots miles and years of experience with both IP and conventional pedaling systems on various tandems. For MB tandeming the freedom that IP allows wins hands down. If you look at our user gallery you can see over 100 photos of tandems many doing single track. Or go to 
http://tinyurl.com/6y9mr3


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## itsdoable (Jan 6, 2004)

*,*



BigNut said:


> ....two riders of equal strength may have said strength at different points of the stroke, and again, the stronger rider at that point in the stroke is pulling the weaker rider's cranks through that portion of the stroke.
> On a da Vinci, there's no chain keeping the two riders synchronized, and therefore, no chain taking power from the stronger rider through the timing chain and "pulling" the weaker rider or weaker stroke section. The stronger rider is relieving some of the effort from the weaker rider/stroke by lessening the resistance, but he is not actually pulling the weaker rider's cranks with his cranks....


There's something wrong with the pedal stroke if this is happening - it would mean that you coast between each power stroke (pedaling squares!). Or one becomes lazy and lets the team mate turn their feet. Cadence can be an issue, I've been poked in the back and told to change gears - I like to spin. I follow Sheldon Brown's tandem advice (the stoker is never wrong), and change my cadence to match - its easy to pedal slower, not as easy to pedal faster.

Most tandem pedal issues are with synchronization when starting or the coast/no-coast transition (lots of communication and practice!), something the daVinci eliminates.


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## Speedub.Nate (Dec 31, 2003)

Curious... Is it easy to remain in-sync with this system?

In both pictures posted, it appears the riders are synced, but it also appears they are coasting.

Seems to me you'd have to both drop to the bottom of the crank rotation and pause for a second, then begin pedaling in unison? Or is this just not a concern?


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## arly (Apr 20, 2005)

*in sync?*

If you look through our photo gallery, your see that in many shots the riders are not in sync. Personally we like to spin and strangely it makes no difference if we're in perfect sync or far from it while riding MB's. In the most recent photos we DLed here, these photos were taken on narrow, technical trail, although the pictures hardly capture that! While riding it either rider is free-wheeling every 100 feet or so to keep their feet from striking a trail feature, like a sharp bump of dirt, rock or log protruding out. If both riders are doing this that often, then staying in sync is difficult or impossible. I ride and stoke with defferent people on a regular bases and we don't have to train them how to stay in sync. Hope that helps. We'll be away on a ridng vaction for over a week, so please forgive us if you don't hear back for a while.



Speedub.Nate said:


> Curious... Is it easy to remain in-sync with this system?
> 
> In both pictures posted, it appears the riders are synced, but it also appears they are coasting.
> 
> Seems to me you'd have to both drop to the bottom of the crank rotation and pause for a second, then begin pedaling in unison? Or is this just not a concern?


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## TandemNut (Mar 12, 2004)

itsdoable said:


> There's something wrong with the pedal stroke if this is happening - it would mean that you coast between each power stroke (pedaling squares!). Or one becomes lazy and lets the team mate turn their feet. Cadence can be an issue, I've been poked in the back and told to change gears - I like to spin. I follow Sheldon Brown's tandem advice (the stoker is never wrong), and change my cadence to match - its easy to pedal slower, not as easy to pedal faster.
> 
> Most tandem pedal issues are with synchronization when starting or the coast/no-coast transition (lots of communication and practice!), something the daVinci eliminates.


Agreed on the stoker makes no mistakes. Reality is, even though we'd all like to think we pedal circles, most folks pedal some semblance of squares, ovals, or other non-perfectly-round shapes. I would suspect that even some of the best and most experienced riders are putting more torque on the cranks at different points of the pedal stroke. It's more pronounced on tandems because the stronger part of the pedal stroke is usually the downstroke, and of both riders are in sync, two riders are loading/unloading the chain. Just watch the timing chain on a conventional (non-IP) tandem and you will very often see it load and unload around the rider's downstrokes.


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## TandemNut (Mar 12, 2004)

arly said:


> Gee has someone ever seen or used this system?? :eekster: Seriously we've been using DaVinci IP bikes for years and can't say enough good things about it,, especially for off-road applications.... ...For MB tandeming the freedom that IP allows wins hands down...


First off, in the interest of full disclosure, I'm a tandem bike dealer (so is Arly). 
I try to be unbiased in my observations of these bikes. Our job as a tandem dealer is to point out both the pros and cons of each brand/type of tandem to the customer, and let the customer decide what works for them.

No one system currently available (that I know of) captures only the advantages of one system (IP vs Conventional) while eliminating the disadvantages of each system.

Here are my observations of IP vs Conventional:

PROS:
1. VERY low low granny gear. 
2. VERY wide range of gearing, far beyond what a conventionally-geared tandem has.
3. Captain and stoker can pedal or coast when they wish, independently.
4. Captain and stoker can set their individual cranks to clear obstacles/click in/out, etc. independently, and also pedal independently to clear said obstacles. 
5. Stoker can set their own pedal for starting without bloodying captain's shins. (This is a big one for us, since Kim gets her payback for whatever transgression I committed this way  )

CONS:
1. Stoker cannot often see obstacles coming in order to set pedals. We personally experienced more stoker pedal strikes with the IP than without.
2. The front 4 cogs are more succeptible to chain suck, especially when muddy/gummy/dirty. 
3. daVinci's bb height is too low, in my opinion, for off-roading. 
Todd Shusterman from da Vinci and I have discussed this, and he disagrees with me on this one, as does Arly. 
But I maintain that IP does not take the place of bb clearance on a tandem.

The above is based on our somewhat unique opportunity to ride various tandems back-to-back on the same trail, same day, same conditions. The observations are from my experience doing just that.

MTBTandems.com sells da Vinci tandems, and we do so proudly. Our next road tandem may well be a da Vinci. But as with all things tandem, for each give there's some take. The IP system solves some problems and for some teams, it is a wonderful option that makes tandeming easier.

I've thought about building a Rohloff/daVinci tandem (at least until Nate bought my spare Rohloff hub) One would probably need only 2 or 3 cogs up front, and I'm not sure if they could be sized to fall within Rohloff's specs. But this might eliminate the chainsuck issue.

The stoker not being able to see obstacles still remains, though.


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## Speedub.Nate (Dec 31, 2003)

BigNut said:


> I've thought about building a Rohloff/daVinci tandem (at least until Nate bought my spare Rohloff hub) One would probably need only 2 or 3 cogs up front, and I'm not sure if they could be sized to fall within Rohloff's specs.


You'll have to get with DFL on that one. That's a 29"er / Rohloff / da Vinci / S & S machine he's building in his thread ( http://forums.mtbr.com/showthread.php?t=410868 ) and I'll bet he's figured out the gearing numbers. I'm envious of this machine he's creating.

You know, for a minute there I contemplated running your Speedhub as a singlespeed...


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## arly (Apr 20, 2005)

*to clarify our IP history*

Just to clarify our history on independent, verse locked timing chains. We started riding tandems in the early 90's and have accumulated mileage of something around 30,000 miles. Started with, and still prefer, locked timing chains for road use, although we did try the IP (Independent pedaling) system for about 1000 miles and eventually decided it didn't add anything to our road riding enjoyment. We tested a bunch of MB tandems, all with locked timing chains but ordered a Da Vinci because of their quad front chainrings, higher timing chains and their reputation of not having the pogo effect on their full suspension bikes. We imagined that we would eventually take the IP off but only after its thorough testing. To our surprise we found it invaluable while on tight single track and didn't have any of the negative effects that we didn't appreciate, while on the road. Something we failed to mention before is while going uphill at very low speeds the IP allows either ride to keep from striking their feet on trail features while the other rider will continue to propel the bike forward. In the below photos you'll see slow, uphill riding situations when the stoker is hesitating to keep her feet off the bridge or rock. And in can be seen that the stoker is viewing the object. Having very high BB's does have its advantages, but also its disadvantages. Folks using bikes built this way commonly speak of "wheel flop" and other low speed handling difficulties and some have added Hopey steering dampeners or other products to help with this effect. YRMV!!


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## TandemNut (Mar 12, 2004)

Arly,
I agree on the slow-speed uphill (downhill, level, etc) advantage of IP. At slow speed, the stoker can see and react to the obstacle independently.
However, at higher speeds, the stoker does not have the time to see and react to some obstacles. That and bashing the captain's timing ring into obstacles we cleared on other tandems was our experience on the IP tandem with low bottom brackets. 
Advantages and disadvantages, just like any system. But IP will not take the place of ground clearance, just like an alternate drive system won't take the place of ground clearance on any off-road vehicle.


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## D.F.L. (Jan 3, 2004)

I have NO time on a Freewheel-equipped DaVinci. The one I had for myself ran fixed cogs, which kept the cranks in-phase... so take this with a grain of salt:

I'd sorta like to see a freewheel with only one pawl and one or two internal teeth. This would allow one rider to coast, but when they rejoin, the cranks would be in-phase again, or 180 degrees out-of-phase. And you might even want some sort of resistance to getting out-of-phase, like a moderate breakaway force.

It seems to me that the Captain needs to make a lot of the decisions, including pedal position, for the vision-obstructed stoker. This seems like it would become increasingly important as the terrain becomes nastier.

Does that make sense?


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## TandemNut (Mar 12, 2004)

D.F.L. said:


> ...
> It seems to me that the Captain needs to make a lot of the decisions, including pedal position, for the vision-obstructed stoker. This seems like it would become increasingly important as the terrain becomes nastier.
> 
> Does that make sense?


It does to me, because it's the same point I was trying to make, in my own indirect, verbose way. Your solution is one that I hadn't thought of, but it makes good sense. Nice outside-the-box thinking!


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