Tandem Timing

[yoothgeye]

Deorman nailed it, pedals out of sync mean there could be a pedal strike when turning, that's bad enough by yourself, but with another person on the bike... yikes.

As for the "engine combustion" analogy, Sheldon talked about this, some tandem riders prefer the pedals to be out of sync 90 degrees forward for the continuous power stroke, but once again, you have a pedal strike concern when cornering.

180 degrees out of sync, or different sized chainrings keeping the sync constantly changing will mess with balance, smoothness, pedal strikes, and generally just make a tandem even more miserable than it already is. haha

As for using 1 chain, it doesn't/won't work. You always need 2 chains.

If you had different sized timing rings, since they are linked together I believe both people would still exert the same amount of force.

 

[junknutz1975]

I myself have never ridden a tandem. Although one of my local facebook friends ( next town over ) , just yesterday , asked me if I was interested in his tandem project. Hmmm ?

 

[GuitarlCarl]

You sync the pedals for balance as you both will naturally balance as you pedal... but also so your feet aren't kicking each other, it's better you know, both lefts forward.. then both rights forward...hehe Riding a tandem takes a little practice to be smooth. The stoker needs to not be over balancing, in fact better not to shift weight at all, pull back on the handlebars and bear down on the pedals. You're the STOKER! Of course, most of us aren't racing...

 

[GuitarlCarl]

a good case for synced... check out that last gear and each pair of gears linked together gets bigger too!

 

[rickpaulos]

I have lots of experience with different size connecting rings and various phasing in tandems & quads.

My first Huffy tandem had 2 different size rings. Yes, it works. One person has to pedal faster than the other depending who has the bigger ring. That can help solve the slow pedaling partner complaint, "you are pedaling too fast". I don't recommend this for criterium racing as the captain never knows where the stoker crank is so you run the risk of scraping the pedal on the pave in high speed cornering. If you have a tandem with high bottom brackets, it won't matter. If you don't go around corners fast, it won't matter. You will get complaints from your stoker when starting if the stoker crank is in a bad spot. Some tandem riders start out with the stoker sitting with feet on the pedals so that's not an issue for them. Others start with both riders pushing off with 1 foot, coast a bit while they get on the seat. That method will be problematic depending on where the stoker crank is.

I have a couple quads that I've tried every combination of crank phasing. Having all the cranks in phase (pushing down with the right crank at the same time) is easy to get started but means the maximum stress on the chain, sprockets, frame and wheels. That also affects steering under heavy pedaling effort. The analogy to a V-8 engine is good for smoothing out the power flow. You are less likely to break chains when each leg takes turn pushing at the maximum power point in the pedal stroke. But having each crank 1/8 of a turn behind another means someone can't push off to get started. The best quad phasing worked out to be 1st & 3rd positions in phase, 2nd & 4th 90 degrees after. Starting works well that way and smooths the power somewhat.

I also built up a cheap tandem with Shimano Front Freewheel cranks. They were used on countless Schwinn Caliente 10 speed bikes that no one wants anymore so they are easy to get. They allow for independent pedaling. Great for beginners. Again, the captain never knows where the stoker cranks are so watch out on corners. Catching a pedal on a tandem or quad isn't nearly the disaster that you get on a single. I've caught pedals many times on my tandems & quads and never crashed. Catching a pedal on a single, crashing is 50%. One draw back of the dual FFS cranks is you lose your coaster brake. You need better hand brakes to substitute. Most FFS cranks are 1-piece cranks so you are limited to installing them on low end cruiser tandems with lousy hand brakes. There was a high end dual freewheel tandem crankset out years ago ($600) for better road tandems. And the IBIS uses independent pedaling (and partially independent gearing) on their tandems. Shimano did make the FFS in a cottered version and a alloy splined 3-piece version but those are quite rare and would be mostly impossible to fit to a tandem.

Rick

 

[GuitarlCarl]

I think the stress on the chain isn't so much... The front gear has the front of the chain as normal bike do, and the rear is actually lifting from the bottom and wrapping over...for lack of a better description... but effectively the rear of the chain. I do think two cranks actually spreads the stress out. The frame flex on my 60's Huffy is the stress I see as needing to be addressed the most... of course it's not a racer either.... and the more modern Columbia I have is less prone to over flexing. I'd like to try a quad once, I'll bet it's FREAKY FAST!

Carl.

 

[yoothgeye]

My tandem frame is a crappy old Huffy with the twin top tubes, dual step through design. I like the idea of using the freewheel crank, but loss of my coaster wouldn't work.

I like all the brainstorming in here, it has enlightened me a lot.