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Shorter cranks for stoker?

Old 04-21-20, 05:59 PM
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124Spider
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Shorter cranks for stoker?

Hi,

We are enjoying our tandem immensely (we've had it for a couple of years, having ridden it several thousand miles).

But we still have one intractable problem: My wife can't generate power at the high cadence I need in order to generate power. I'm a lot taller than my wife, with legs at least 15% longer than hers. And yet, on our tandem, her cranks are 170, and mine are 175. I would think that her cranks should be 15% shorter than mine.

Has anyone here tried much shorter cranks for a much shorter stoker, and, if so, did it help?

Thanks!

Mark
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Old 04-21-20, 09:52 PM
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Yes. It helped her. Our bike came with the same crank lengths that you have. I like the formula 5.5* inseam = crank length in mm., inseam meaning the standing in your socks, a book in your crotch method, not pants inseam. For my stoker that worked out to 149mm. I bought a shortened stoker crankset from these folks: Short Bicycle Cranks
They provided the 172.5 version shortened down to 151mm Your ideal crank length spec might be different.

The shorter cranks have worked out well for us. I think we're a little slower on the climbs because cadence is lower and so her leverage used to be greater, but maybe a little faster on the flats and shallow or short climbs because we can use higher cadence effectively. She much prefers it anyway and that's the end game.
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Old 04-21-20, 10:07 PM
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If you want to experiment with different lengths without committing to a full crank replacement you might try this: https://www.sjscycles.co.uk/componen...eners/?geoc=US
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Old 04-21-20, 10:40 PM
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An interesting article on the topic: https://bikedynamics.co.uk/FitGuidecranks.htm
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Old 04-22-20, 08:39 AM
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You can definitely use crank length differential to sort out cadence mismatch. Your intuition is correct that shortening your stoker's cranks would let her comfortably spin -- and make power -- at higher cadences. You can also put longer crankarms on the front for a similar effect.
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Old 04-22-20, 08:52 AM
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Originally Posted by 124Spider View Post
Has anyone here tried much shorter cranks for a much shorter stoker, and, if so, did it help?
I'm 6' and beloved stoker is 5'. Can't remember exact leg lengths, but believe they fit within your 15% difference.

I use 175mm cranks on the tandem, and she has found she *must* have 165mm cranks on her bikes, including the tandem.

As a data point, we did a test ride on a stock tandem with 175mm/170mm cranks and she began experiencing knee pain within 10 miles of easy riding.

Getting her the correct crank length drove us to sourcing rather pricey Lightning cranks on our Machiatto, but they are worth every penny.
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Old 04-22-20, 09:32 AM
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If one has stoker crank length sorted, a very effective cadence drill is to take it up to a steady 100 cadence on some fairly flat terrain and hold it there for about 30 minutes continuously, shifting as necessary. We do it in HR zone 3. We've found this works better for both of us on the tandem than on our separate trainers, I suppose because the tandem is our primary outdoor bike.
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Old 04-22-20, 09:33 AM
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See, not an intractable problem. Tandems are so much fun.
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Old 04-22-20, 09:55 AM
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Thanks all; we'll give it a try!

I've ordered her a set of 150mm cranks.

Last edited by 124Spider; 04-22-20 at 02:48 PM.
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Old 04-22-20, 02:11 PM
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I'm 6'3" while my wife is 5'1", and we've been riding 175/165 since the mid '80s. I don't exactly recall how we determined her crank length, but I do remember that we struggled with cadence just a bit when we first started riding a tandem. I'm assuming that my wife went from 170 to 165, but we haven't had any problems since.
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Old 04-25-20, 03:32 PM
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Originally Posted by 124Spider View Post
Thanks all; we'll give it a try!

I've ordered her a set of 150mm cranks.
After a few rides, let us know how that worked out .
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Old 04-25-20, 08:49 PM
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Originally Posted by Carbonfiberboy View Post
After a few rides, let us know how that worked out .
I certainly will!
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Old 04-29-20, 07:13 AM
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A while back, I measured my me and my wife's inseams. I took the ratio and got crank arm lengths that matched. I was running 170 and she was 155. It worked okay but not great. With the latest crank set, I got her 170 and me 175. She has a hard time spinning so is more comfortable with putting out power so the added leverage works better for us.
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Old 04-30-20, 05:32 PM
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The new (150) cranks arrived yesterday, and I installed them. We went for a ride today, and preliminary results are very encouraging!

For this particular ride, I would normally average around 84 rpm on my half-bike, but I would keep to to around 79 on the tandem. And my stoker would struggle with that.

Today, we averaged 84 rpm, and my stoker's power was significantly up from normal. Subjectively, she felt much more comfortable at higher revs than before.

So far, so good!

Mark
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Old 04-30-20, 10:18 PM
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Which cranks then?

Did you buy the Sinz cranks? If so, did you weight them?
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Old 05-01-20, 01:14 PM
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Originally Posted by Scottgps View Post
Did you buy the Sinz cranks? If so, did you weight them?
We bought da Vinci cranks, to replace da Vinci cranks; easier, since the rings attached to both of stoker's cranks don't have to be replaced. I did not weigh the shorter cranks; our tandem weighs over 50 pounds, and a few grams this way or that isn't much of an issue.
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Old 05-30-20, 03:48 AM
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We assemble connecting rods with different sizes and there is no problem Shimano Lx 175 and 172.5 cm MTB Road 172.5 and 170 I don't know
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