Crank Arm Length

[Enso108]

I'm been thinking about what crank arm length I should be using on my fixed, according to the crank arm calculator on the interweb I should be using 172.5mm, I currently use 175mm. I read somewhere that with a longer crank arm gives more leverage, but a shorter crank arm is better for a higher cadence. My question is will a few mm's make much difference to a non competitive plodding fella like me.:?:

 

[ianrauk]

not in the slightest methinks.
Have a look at 2.5mm on a ruler...

 

[Will1985]

It'll could make a difference if you corner hard - the difference between getting round safely, and grounding the pedal before being thrown off!

 

[Enso108]

It'll could make a difference if you corner hard - the difference between getting round safely, and grounding the pedal before being thrown off!

Got to be honest I'm really one for hard cornering Will, but would 2.5mm really affect my cornering ability?

 

[Will1985]

2.5mm probably only affects it by a degree or two so not massively. Another factor to consider is the size of the pedal; it may or may not be a coincidence that the occasions where I have had pedal strike have been when using chunky Look Deltas rather than small SPDs (and I'm on 165mm by the way!).

 

[fossyant]

Don't worry about it. 170mm on all my bikes, road, mtb and fixed....

 

[TheCyclingRooster]

Hi to you all.I can relate to the subject of Crank Arm Length from a different direction and it may serve to help those that hang on in with my input.I am very short limbed (23.5" inside leg)(4' 10" tall) in bare feet.I ride a big boys bike so stand over height has always been a source of amusement to onlookers.I have always ridden regular 170mm cranks untill my replacement knee surgery in Nov 07.Short limbs, long cranks & restricted knee bend don't work.I got my head around the problem by scale drawing my problem on the drawing board and came up with a crank arm of 140mm being needed(www.sjscycles.com provided me with the answer,other sizes are available in short increments from 130mm -175mm.Stronglight rings 110 BCD & 74 BCD allow upto a triple on a 5arm spider.The use of a 140mm crank has the same effect as a 2 tooth larger chainring(approx 17.5% greater effort than regular 170mm cranks).At the high end it is great(higher gearing than normal if desired and in the low end on my Bianchi down to a 26t inner on the triple.The set up is 52:42:26 without a hickup and 13:14:15;16:17:19:21:23:26 on the rear.The clearence on the pedals is 115mm at the low stroke(Marcel Berthet Lyotard Platforms with Christophe Clip & Straps).If I fit the Shimano PD-M520 it will increase by only 5mm but the lean angle will increase by approx' 10* by which time you are well on your way to Macadam Rash.To sum it up, short cranks with fixed gear and a wise choice of gear inches will give a Cadence as smooth as whipped cream and help to prevent "tip off" when fast tight cornering is mastered.Happy & Safe Riding to you All.

 

[Enso108]

Thanks Rooster thats really interesting.

 

[Greenbank]

Another consideration is the frame.

Most frames specifically designed for fixed (or the track at least) will generally have a higher BB than a random conversion using an old frame with horizonal dropouts.

I use 172.5mm for the geared bikes and 165mm for fixed. I can't tell the difference the different crank lengths when I swap between the bikes.

It's entirely personal, but for fixed my main limitation is my (in)ability to spin (only up to 185rpm, some way off the fabled 200rpm) so I went for 165mm cranks rather than anything longer.