Cadence incompatibility is one reason why some teams don't enjoy tandeming or don't perform as well as they might. Adjusting crank lengths is highly effective at fixing this.
Some stokers may do OK with 170s on their single bikes, but at a slower cadence than their captains. Perhaps because they ride less and/or have shorter legs. When you put them on the same bike, with similar crank lengths, the only cadence where both are working effectively is a narrow range that includes the high end of the stokers useful RPM and the low end of the captains. (Assuming they overlap at all.) Poor combined power output and lots of shifting is the usual result.
Example; Stoker 60-80 rpm, Captain 75-95 rpm = Team 75-80 rpm. When one rider's comfortable cadence is 70 and the other's is 90, going from 170 to 165mm, about 3%, isn't going to make a noticeable difference when trying to increase the stoker's comfortable RPM by 28%. In a perfect world, lengths would be such that the stoker's and captain's efficient RPM ranges would be matched. But lacking perfection, getting the overlap wider will get the bike down the road better.
I've sold a couple of dozen shortened tandem stoker sets. Most have been 153mm or 148mm with a few even shorter. I just sent off a set of 140s for the rear of a 1980 Gitane tandem.
Shorties not only raise a riders comfortable/efficient RPM range, but in most cases the range is wider. Usually losing little if any off the bottom and gaining quite a bit on the top end. Great for single speeds. You can gear lower and still have a decent top speed.
These two are typical of the feedback I get: "I got the cranks two days ago, and about ten minutes later, they were on our tandem. The next day, we went for a ride, and boy, was she happy to be able to pedal those little circles!"
"In hindsight, I greatly erred in not getting my previous partner shorter cranks. Our ranges had no overlap, and my wishing that her range would come up to mine didn't happen. I've grown up a bit since then.
Back to the present, now that I have the short cranks on the back of my present tandem (thanks to you), I no longer over-rev my partner. In fact, I've really let the RPMs come up, and have asked her if she is still okay, and to my surprise (and delight), she is still okay. "
At 1:56 AM -0700 1/16/11, mrrabbit@mrrabbit.net wrote:
>5. Cutting in half doesn't do any good when getting a divorce.
I know of one case where he got the components and she got the frame.
Mark "Do you still call it a 'Snot Rocket' if it doesn't get past
your stoker?" Stonich
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