Crank Length ?

[Betsy]

I've just got sucked into this article.. it's quite an enjoyable read.

A Riders Guide To Crank Length

As someone who has always ridden 170mm MTB cranks without ever giving it a second thought.. i decided to 'give it a second thought' .. i'm getting older, Ikr.. hard to believe and i am getting a litle knee pain after a 6hr Sunday ride.

In hindsight, the only reason i decided to ride 170mm is because i had 170mm cranks on my first GT Karakorum, i was young and bouncy, it felt right (going from BMX to MTB) so i never gave it a second though and i've ridden 170mm ever since under the .. 'if it isn't broke don't fix it mantra'..

I pulled out the tape measure and started measuring lower body parts and according to the above, maybe 165mm would work better for me.

 

[Takingabreak]

There's no looking back once you try 165mm cranks. I can confirm they are perfect for 6 footers with creaky knees

 

[Woz]

Sugino for many years gave some rough quick guidance:

https://www.suginoltd.co.jp/us/products/accessory/images/chainring-message.gif

 

[Markybeau]

The difficulty is in finding them. I've got many sets of 170mm but only one of 165mm - in retro models

 

[bikeworkshop]

165 is laughably long according to the new Bicycle Ideology.

Short cranks suit sitting and spinning, like small gears, and old knees

 

[Betsy]

Another thing to consider is the effect of pedals and footwear..

For instance, a crank measurement of 170mm would be taken center to center but if you're riding fat / flat pedals, something akin to Base Jump or Club Roost 2D.. they would measure 25mm deep or 12.5mm eaither side of spindle center.. then a pair of Vans only measure 8mm ish from footbed to outsole whereas a pair of Nike with a foam midsole would be closer to 14mm.. add the 2 measurements together and this would decrease the length of the crank by 20mm on the downstroke and increase the length of the crank by 20mm on the upstroke..

 

[bikeworkshop]

Another thing to consider is the effect of pedals and footwear..

For instance, a crank measurement of 170mm would be taken center to center but if you're riding fat / flat pedals, something akin to Base Jump or Club Roost 2D.. they would measure 25mm deep or 12.5mm eaither side of spindle center.. then a pair of Vans only measure 8mm ish from footbed to outsole whereas a pair of Nike with a foam midsole would be closer to 14mm.. add the 2 measurements together and this would decrease the length of the crank by 20mm on the downstroke and increase the length of the crank by 20mm on the upstroke..

Pedal and sole thickness Raise the effective circle of pedaling, so require a higher saddle and raise your centre of mass.
It doesn't alter the effective crank length.

 

[Betsy]

Riding in a cuban heel isn't giving me a happy medium?

 

[bikeworkshop]

There was a fashion in the 70s? for "Ankling", pushing your toe down on the downstroke.
Cuban heels perfect

 

[Woz]

Flip flops or high heels. We've seen it all.

The original Look clipless with the shoes were monumentally higher than the toe-clip versions that you almost wondered you needed a bigger frame. SPDs have been fairly regular in height from axle. I can appreciate flat pedals can vary but still the overall difference is crank length.

The article is a good read. Personally, I don't have a problem with knees and the bent hip - leg angle at top dead centre - it's my feeling at bottom dead centre I have a problem with and am sensitive to crank length. 175mm for me as I feel "too bunched up" otherwise with no feeling of leg stretch. I can often get cramp, so every so often a good proper leg stretch on the downstroke with ankle down works.

A lot is probably conditioning over time what you started with - how we got here is for a historian, and we already know most related to position and bike fit is based on very early statistic data in a road racing environment.

170mm cranks I do notice and just seem to bugger about with seat height forever and never feel totally happy. OK messing about for errands fine, but it does bug me. Road bikes I seem less likely to adapt to because of this being standard. I am according to my height of the Sugino guide at the very "lower end of 175mm" to be right.

I sacked off all 170mm road cranks on my CX bike years ago for 175mm MTB cranks because I hated the transition feel of switching bikes and it was the best thing I did.

Everyone is different, a bike is a self propelled machine with a lot variables for the engine to work. Some are more sensitive than others.