Crank Length

spinndrift

I'm currently riding 172.5 cranks on the Fuji but will be getting a new bike in a few weeks and can spec the crank length I want.

So my question is am I best sticking to the same length or should I change and also if I change lengths will I need a period to adjust before I ride LEJOG in June?

mattshrops

a bike fit will tell you the correct length cranks.

i think the rule of thumb is if your legs are long for your height go 175, average 172.5, short 170. realistically its 2.5 mm if youre going well as you are why change?

ShutUpLegs

Probably dependant on frame size/ fit also

gwillis

I recently purchased a carbon Athena set up and swooped the alu 170 crank on my one bike for a carbon 172.5 to be honest I can't feel the difference .

craker

I'm on 170mm on my commuter and 175mm on my others. I can tell the difference but it doesn't make any tangible difference.

cougie

I really can't tell the difference. 170 used to be the standard length.

colsoop

Will depend on you really. But if you change the length you should adjust the saddle height in relation to that change - be it up or down depending on the length you have changed the cranks too.(assuming your seat height is right of course)

I am on the small side and after my bike fit the ideal crank length for me was 165mm but i currently ride a 170.
The bike fit guy said the 165mm would give a bit more room at the top of the pedal stroke and reduce the dead spot at the top of the stroke.

These are the sort of things that a dynamic fit will pick up on and are definitely worth having a look at if you aren't 100% sure on the crank length to choose.

MichaelW

mattshrops wrote:

i think the rule of thumb is if your legs are long for your height go 175, average 172.5, short 170.

Its more to do with the absolute length of your legs (specifically upper leg). Crank length determines the angle through which your hip moves. If the angle is too great, you cant spin, if it is too small, you cant apply your full power. Draw the geometry of pedalling action on paper and all becomes clear.

Should you change from 172.5mm?
For average male 5'10", a normal crank, by tradition, is 170mm. You can go up to 175mm depending. I have 175mm on one of my bike, I ride it a lot but feel the lack of spin.
If you are a different size, your "normal" size crank will be different.

floosy

Indeed It mattters. Shear forces throught the knee etc...

Its more prominant if you are shorter than average....

Me im 5`1" tall and have 155mm Cranks on road bike and 160mm on MTB..

Dave..

Berk Bonebonce

The way a pro would do it is by trying cranks of differeing size. I believe Stronglight do an adjustable crankset that offers the three traditional sizes ... every decent club should have one.

derosa

Crank length should relate to the length of the femur. My long legs need 175-180 cranks. When I try 170's it feels like I'm riding a kids bike.

Wheelie Bin

Have you ever been half way through a ride and thought... "my god, I wish my cranks were 2.5mm longer!" ...?

I'm 5'10" and my recent bike fit was on 172.5mm cranks, if that helps.

rake

derosa wrote:

Crank length should relate to the length of the femur. My long legs need 175-180 cranks. When I try 170's it feels like I'm riding a kids bike.

me too. only taller people seem to notice this which is probably logical. i can tell between 170 and 175. the 5mm is the radius so actually makes 1cm difference to the full leg movement . also the power around a circle isnt linear with its diameter rather like area of a circle isnt.

smokeysmoo2

Crank length is pretty much purely an anatomically personal decision. However, there are a lot of crank length calculators around, eg: http://www.nettally.com/palmk/crankset.html. Be warned though, you may get a surprise result, apparently I need a crank length of about 190mm! Yet I ride 175 on my road bikes, and 165 on my fixed bikes without any issues at all, hence my first sentence.