Crank Length for TTing

ridleydan

Hi all,
I have just bought a second hand bike for time trialling and currently it is fitted with a 170mm long campag mirage crankset. i was looking to fit a 42T inner ring along with the 53T outer, but was wondering, as my road bike was sized for me with 172.5mm cranks, should I just go ahead and change the lot?
Would longer cranks not to be better for TTing so as i can push a larger gear at a slower cadence?
Any recommendations?

Thanks

kenbaxter

TT'ing isn't always about large gears and low cadence! Whats your riding style, think about that and then maybe get the crank length that suits. When I'm tt'ing my cadence goes up from its normal 80-90 to 100-110. I went from 175 to 172.5 cranks last year (nice carbon ones on offer!) and frankly can't tell the difference!

If in doubt try them out and see if you can tell!

Garybee

I'm the opposite to ken. I make more power if I drop the cadence to 85-90 from my usual 90-95. I also can't tell the difference with the small changes in crank length. I had 170s on my training bike (it came with them) despite having 172.5s on all the rest. Broke the 170s a few weeks ago, replaced them with 172.5s and wouldn't of noticed if someone had switched them without my knowledge.

ridleydan

My thinking was the longer the cranks the more leverage i could apply to push a bigger gear at the same cadence. i remember reading or being told that TTists tend to up the crank length?
If this is wrong, please correct me.
The 2.5mm difference in crank length is nearly 1.5% of the overall length of a 170mm crank, will this equate to 1.5% addition to my current TT times? as I have 1.5% less leverage.

geoff_ss

ridleydan wrote:

My thinking was the longer the cranks the more leverage i could apply to push a bigger gear at the same cadence. i remember reading or being told that TTists tend to up the crank length?
If this is wrong, please correct me.
The 2.5mm difference in crank length is nearly 1.5% of the overall length of a 170mm crank, will this equate to 1.5% addition to my current TT times? as I have 1.5% less leverage.

Unfortunately you don't get owt for nowt in the real world. Speed comes from leg strength and cardio vascular fitness more than anything else.

Increasing crank length provides more torque but so does lowering the gear ratio. I'm sure there are skeletal mechanical reasons for improving pedalling efficiency by matching crank length to leg length but, for a first approximation, there's no difference between changing crank length and chain ring/rear sprocket size ratio.

It's like saying you can ride your bike at 100 mph if you have a high enough gear ratio. In fact you can often go faster by lowering the ratio as I always found when attaching a sidecar to a standard motorcycle.

Geoff

ellieb

If it is any consolation I found that my Trek had come with one crank 170mm & the other at 172.5mm. The only problem was that I'd been using the bike for over 2 years!! I had never even noticed. Good job that one of my legs is longer than the other :roll: