Crank lengths - make a difference?

My road bike runs either 170/172.5 is there really a difference if I use 175? Will my knees, legs whatever notice a difference?

Nope. May need to lower your seat a tad.

i stopped using these omniums because i didnt realise i got the 172.5 ones, had a few occasions when going round a corner at speed i would get hench pedalstrike, it threw me off once. if youre on a roadbike its not as much of an issue but 175 seems a bit long for most people

inb4 shit fixie skidders say

crank length doesn't really matter - it's a question of preference really.
If you ride with others shorter is better on your own longer.
I use 175s but I'm 14stone and I need some leverage to hoist myself and steel frame up the climbs.
This I do slowly.

http://www.cervelo.com/en/engineering/ask-the-engineers/crank-length.html

http://sheldonbrown.com/gain.html

Depends on your leg length I reckon.
I moved from 165's to 172.5's and the change was a massive improvement. I am a 35" inseam though.

I had 165 on my fixies, but after riding some time on 175 on my cx I swiched my track cranks to 170. Feels much better. The 165 feels like riding a kids bike.

181 with 86 inseam here.

makes a huge difference in the feel.

i don't ride anything other than 175.

After riding fixed 165 I switched my road cranks from 175 to 170mm. I found with the 175s I was locking out my knees on occasion and finding I was a bit cramped at the top of my stroke. My spinning didn't feel as fluid.

Still evaluating 170's, I'll need to tweak the seat and bar position, but it feels much more comfortable spinning on the roadie now.

Yep. Mega difference for all the reasons above.

They say to start with 9.5% of your height and you won't go far wrong.

I'm 173cm with short legs (30" inside leg) and find 165s the best for me.

I got 172.9 and the bike has 175. Will live with them for now and change to something smaller when I have some spare cash.

cheers

There's quite a lot on this if you google around. All things equal - i.e. you change your gearing to compensate - I suspect the difference between 170-175 for folks on medium to large frames is negligible, but if you have shorter legs you might feel it.

They say to start with 9.5% of your height and you won't go far wrong.

But where do they get 9.5% from?

If you consider the range of crank lengths commonly available (165mm to 175mm, or 10mm) and compare that to inside leg measurements (61cm to 94cm, or 330mm) , it's difficult to see any meaningful correlation.

If you trawl the web, you'll find plenty of crank-to-leg-length calculators, but never an explanation as to how they arrive at the number you multiply your measurements by.

All very scientific looking, but like much psuedo-science, they seem to be making the mistake of knowing the answer they want and tweaking the formula to produce it.

All very scientific looking, but like much psuedo-science, they seem to be making the mistake of knowing the answer they want and tweaking the formula to produce it.

Think about it dude - looking at known facts and working out the maths behind them isn't pseudo-science, it's actual proper science.

In this case there isn't as precise formula as physiology differs so much, but it's good to have a starting point.

Went from 165 to 167.5 to 170 to 172.5 to 175. I'm 190cm with an 84cm inseam.

I found that 165 and the 167.5 was waaay to spinny on a commuter gear of 47x17.
170 was ok but felt I couldn't really get the power down.

172.5 is my current length and it's a good balance between a good controlled mash stroke and a nice fluid spin on 49x18.

165mm on my fixed gear bikes to avoid pedal strike.

170mm on my ss MTB to balance leverage on climbs with spinning on flats/descents.

175mm on my adventure/touring bike for max leverage and because the larger circle the pedals make means my legs are flexed more in the hope that this will stave off cramping and lactic etc.

What didn't I mention?

^ Gain ratio innit.

Which is a consideration when choosing the length of your cranks. As is pedal strike. As is the stress on your knees.

But there is no need for longer cranks because you have longer legs: your legs describe a circle, not a straight line when pedalling.

If anything, there is an argument for shorter cranks with longer legs to produce a less acute angle at the knee, at the top of the pedal stroke.

5mm longer cranks mean dropping your saddle by 5mm, which means your knee will be 10mm higher at TDC. This increase the amount of shear at the knee, ie your femur will be trying to push over the top of the tibia, more than it would with a shorter crank.

Ouch.

170mm fixed. 172.5 on 'owt with a freewheel.

pedal strike only ever happens with big flat wide platform pedals.
never with look keos.
or at least not yet.

Gain ratio innit.

Nope.

I'm the same height when I commute to work on my fixed as I am when I pack my tent into my panniers and head away for a weekend.

Page refresh fail: that was in reply to Thrust. :)

It's all in your head.

The difference between 170, 172,5, and 175, for the averge hieghted person is pretty small in reality. As a shortarse my ideal crank length is 161mm I think. So I ride 165mm on everything. Definitely feel like I'm over extending on 175s. Which I use on the SS 29er for leverage. But the fact that I dont mind them despite them being in theory 14mm too long. Shows the insignificance of the 2,5mm difference between the standard sizes.

your a crank!

You're........

Smallfurry is correct, listen to Smallfurry.