Keen to get some thoughts on crank length. We were always told to run longer cranks on our TT bikes to get greater leverage and power but the attached PDF questions that idea.

Hmmm, fascinating! As I said to Kelly last night, there don't seem to be hard rules - what works is best, but I guess trying shorter and shorter and measuring power/efficiency isn't easy for most riders. Also this seems to be mainly TT/tri use - do you think it applies for road riding with the constant changes of rhythm?

Perhaps he should hang onto his 170s!

Think they did a study where riders went from 150mm to 200mm cranks and didn't really find too many differences.

I am 172.5cm tall and use 170s when most would suggest 172.5mm. I have been running 165mm on my track bike which I have been using for road TTs. Pretty same set up and better wheels on my road bike but 90sec faster on my track bike. Drive chain efficiency would be the primary factor but wondering if crank length is also relevant.

Wouldn't a riders pedalling style influence crank length choice? I'm a stomper rather than a spinner so prefer longer cranks.

I have very long legs for my height, and by some formulas should run 180s (or much longer according to Lennard Zinn!) yet have always been happiest on 172.5s - I raced for a few years on 175s but found that as soon as I got tired my pedalling got really choppy, whereas with the ridiculously small difference of 2.5mm it didn't. Go figure.

I always ran 165s on my track bike for the leg speed...

And yes, Tama. You're quite right.

I was talking to an old mate last night about this very thing. Back in the mid 80s there was a study done on BMX racers. They put them on many different lenghts from 100mm to 250mm. Results were that shorter cranks were better but at the time guys were running 180, 185 and even 190. (disclaimer, this is second hand). But what was said was that there was a high placebo effect in people riding what they thought they needed.

Oli wrote:I have very long legs for my height, and by some formulas should run 180s (or much longer according to Lennard Zinn!) yet have always been happiest on 172.5s - I raced for a few years on 175s but found that as soon as I got tired my pedalling got really choppy, whereas with the ridiculously small difference of 2.5mm it didn't. Go figure.

I always ran 165s on my track bike for the leg speed...

And yes, Tama. You're quite right.

I have 170s, 172.5 and 175 on different bikes. I cant feel a difference.

I can. HTH(I'm a twerp).

Oli wrote:I can. HTH(I'm a twerp).

Me too.

jo wrote:

Oli wrote:I can. HTH(I'm a twerp).

Me too.

Ditto - 170mm, 175mm and 180mm across my bikes.

Spokes wrote:I was talking to an old mate last night about this very thing. Back in the mid 80s there was a study done on BMX racers. They put them on many different lenghts from 100mm to 250mm. Results were that shorter cranks were better but at the time guys were running 180, 185 and even 190. (disclaimer, this is second hand). But what was said was that there was a high placebo effect in people riding what they thought they needed.

If it's the same one I'm thinking about they found pedalling action was far more important than crank length when measuring speed.

Oli wrote:I can. HTH(I'm a twerp).

Well I think its because the 170mm bike is clips and the others are flats.

When I was young I ran 180s and could notice that.

So thinking of on the mtbike... where you often need short power bursts to get over obstacles before resuming cadence... would a longer crank with more leverage give you better acceleration to get over a rocky section of track??

Wow that was really interesting, I hadn't thought about pedal speed before which does seem to make sense, going from 175 to 165mm cranks your foot travels 64mm less and even a change of 2.5mm equals a 16mm difference in how far the pedal travels every rotation. So to me, on flat ground at a high cadence that must translate into a noticeable difference in efficiency. I found it pretty amazing how much it effected the aerodynamics too.

Trail wrote:So thinking of on the mtbike... where you often need short power bursts to get over obstacles before resuming cadence... would a longer crank with more leverage give you better acceleration to get over a rocky section of track??

Yeah I would think a mountain bike would benefit alot more from longer cranks, and even in road cycling where you've also got hills you would definitely need the longer cranks.