Tandem Cycling - Optimal crank length for hilly terrain
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We purchased a Cannondale tandem this spring and are enjoying it immensely. We ride in a hilly area here in southern PA and I have wondered if changing my (captain's) crank arm length would make a noticeable difference when climbing. It's difficult to figure out the tradeoffs between leverage and longer range of motion and integrate this with my longer/stronger legs vs. my stoker's shorter/less strong legs. How does it all work out? I'd be interested in any experienced tandemer opinions.
You should get cranks that fit. The terrain really should not be a big factor in this; you generally want to spin more than slog, especially on a tandem, where standing is less automatic. I have recently gone from 175 to 170 for a much nicer experience (having ridden 170's for 30 years). I don't know why the market seems to be going for longer cranks, but it is actually hard to get 170's in the captain's position these days.
08-17-08, 12:48 PM
What length crank do you ride on your single bike? If those work well for you, I'd use that length on the tandem.
As for the stoker I'd do the same. Only difference being on a tandem would be matching cadence. In general, shorter cranks favor spinning, longer cranks favor lower cadence. So theoretically if one of you went to the extreme long end for your size, and the other to the extreme short end it might make it more difficult to find a good candence for both of you.
However if you both get cranks that fit you, I think you'll be fine.
08-17-08, 06:20 PM
What length crank do you ride on your single bike?
If those work well for you, I'd use that length on the tandem.
I spent all last summer experimenting with crank arm lengths on our Tandem because after using 170 arms on all my bikes for many many years, I bought a Cross bike that I ended up really enjoying and it had slightly longer arms than I had on our tandem. So I read everything I could read on the internet, tried all the different calculatons from several different sources for the perfect length, bought longer arms (175 and 172.5's), tried this and tried that..... when the day was done I went back to my original 170's simply because I could spin better on the tandem with the 170's. And in my book, spinning is king on a tandem.. particularly in the hills.
My experience is that for general riding, 5.29mm of crankarm length, per inch of inseam, works best. I always provide the best length for my stokers when I can. Presently the tandem I ride with my wife has 185's on the front, and 162.5's on the back.
Cadence should vary inversely with crankarm length, but that would be difficult on most tandems. I don't worry about it much, because I find few people want to match my relatively high cadence.
You ask if there would be a noticeable difference. The answer is, heck yes, as noted above by others, some of us can tell. I imagine I might have difficulty with noticing only 2.5mm of difference (170 to 172.5, for example), but I bet I would be able to notice 5mm (180 to 185), and the best size does make you faster. Go ahead, tie your legs together and go for a hike. Slower? Uh-huh, well, that's what too-short cranks do, they make you take shorter steps.
My experience is that for general riding, 5.29mm of crankarm length, per inch of inseam, works best.
This is the first time I've seen a figure that allows one to calculate crank arm length at all, so it's a good starting point. This formula recommends I ride with 170's, which I did for decades. But I have now discovered 140's suit me better.
I always provide the best length for my stokers when I can. No doubt that's good policy.
Presently ... I ride with ... 185's ... to match my relatively high cadence.
OMG that's a long crank arm for a high cadence!
You ask if there would be a noticeable difference. The answer is, heck yes, as noted above by others, some of us can tell. I imagine I might have difficulty with noticing only 2.5mm of difference (170 to 172.5, for example), but I bet I would be able to notice 5mm (180 to 185)
Yes, that is my experience too; back when I rode 170's, 172.5 felt okay but 175 definitely felt too long.
the best size does make you faster. That is no doubt true; but what's the best size? I have found very little research into this question. How do we determine the best size?
Go ahead, tie your legs together and go for a hike. Slower? Uh-huh, well, that's what too-short cranks do, they make you take shorter steps.
No, not like that. At a given gear ratio, one revolution of the pedals is going to take you a given distance, regardless the crank arm length. For comparison:
On your 185mm crank arms your feet move 1162mm per revolution, about 4'
but with 140mm crank arms my feet move 880mm per revolution, about 3'.
So if we're pedaling along at 60 rpm, my feet are moving 3 feet per second, while yours move at 4 feet per second.
Obviously this will have some advantages and some disadvantages; but I have been finding that for my riding style there are mostly advantages.
08-22-08, 02:16 PM
I you go from 170's to 175's you should lower your seat by 5 mm in order to have the same leg extension on the downstroke. which means that your leg will come 10 mm higher on the upstroke. This can have implications for your knees. My wife's knees bother her if she uses anything longer than 165's. (We have 170/165 on our tandem.)
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