Pro rata sizing of tooth count vs. crank length.

bristolpete

Sounds odd I know, but if one drops crank length at the behest of a bike fit should the chain ring tooth count adjust too?

I ask for myself as moved down to 165 crank arms which my hips and knees love (I have very short inseam) but still running 53/39 on the front, 12/25 on the back. I ask as my usual training loop has become harder - it is as if someone pulls the plug on me on one hour 30.

Logic tells me that I should drop to a 50 now, and sustain cadence and choose a cassette of which the 12/25 has never been an issue til now.

I am a bit depressed about it all to be honest as the other caveat would be a different cassette, but I think the fatigue stems from the front not the back if that makes sense ?

Any advice out there?

Thanks,

Pete.

smidsy

If you have gone to a shorter crank you obvioulsy lose some leverage (as the distance from the pedal to the BB has reduced) but if it is only a few mm is should not make a massive difference.

Perhaps the conditions (yours or the weather) were more to do with the difference?

ShutUpLegs

bristolpete wrote:

I ask as my usual training loop has become harder - it is as if someone pulls the plug on me on one hour 30.

Is this a one off ride or consistently happening?

Also, you may get better answers if you post in 'Training'

Slack

It only 'appears' harder at this stage. Your muscles will gradually adjust, and you will soon find yourself pushing through the stroke much more efficiently, turning smoother circles.

MichaelW

See Sheldon Brown's discussion of Gain Ratios.

itsnotarace

http://www.sheldonbrown.com/gears/

Crank length is a variable of the calculation so just put your figures in and it will calculate it for you