[HJR]

Good morning. I recently got my hands on a tri bike and I have set it up with extra parts I had lying around. Anyways, to the point. I only had a 170mm crank. I run 175s on my road bikes. I remember reading once (don't remember where) that a shorter crank arm on a "flat" course would allow for a smoother transition to the run and allow for a higher cadence. True or not? Should I find a 175 crack for it?

Thanks in advance for any and all help.

[The BikeForums Team]

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[audiojan]

I don't know if it would allow a smoother transition, but it does promote higher cadence, i.e. it's easier to get comfortable spinning with short cranks. But the penality is that you will not have the same leverage, thus you could reduce your power output (unless you can make for it by having a higher cadence...). Another drawback with a too high cadence is that your heartrate will probably be higher, not necessarily a good thing...

[Dubbayoo]

I don't know if it would allow a smoother transition, but it does promote higher cadence, i.e. it's easier to get comfortable spinning with short cranks. But the penality is that you will not have the same leverage, thus you could reduce your power output (unless you can make for it by having a higher cadence...). Another drawback with a too high cadence is that your heartrate will probably be higher, not necessarily a good thing...

Some people run longer cranks on their TT bikes than road and you're looking at going 5mm (which is two sizes) shorter....sounds like a lot to me. For me it depends on your physiology. If you're Lance Armstrong with lung capacity to spare then spinning is the way to go. If you're Jan Ullrich with leg power to spare then lower cadence/longer cranks is the way to go. I would AT LEAST go with 172.5's but I'd prefer the 175's.

[TysonB]

My U08 1969 has an odd and short length of crank arms: 168.5mm. The guys on the vintage forum say that this wasn't all that rare back in the day. I think it hurts a bit to have such short cranks in that the loss of leverage makes itself known at the limits. I have trouble pushing the same gears that I push reasonably easy on similar bikes with longer arms.

None of this is scientific, just anecdotal. Sheldon Brown has on his website, a complete discussion of the ins and outs of crank arm lengths that you might find enlightening.

Tyson