Zinn's cranklength formula

[gregblow]

Anyone ever used this formula to get a pair of cranks? Any thoughts? I used the bike fit formula. Seems like it got me more comfortable. It is a bit outside the "normal" bike fits I have gotten in the past. I am now looking at doing a custom crank length, it says I need a 180!

www.zinncycles.com

[tiretrax]

It's a range, so multiply your inseam in mm by .21 and .216 to get the optimal range. I was 175-180. I have a 175, and it's comfortable and seems to get a full range of power. I remember the theory that shorter crank arms were optimal because the rotation was completed more quickly, so good for spinning.

[Mark McM]

I wouldn't put too much stock in that formula. The recommended crank length range is based on a blog post, which based on a thought experiment. Real world testing of crank length has yet to find a good correlation between crank length and efficiency. As of today, the only data based recommendation that can really be made is to use what ever length crank is most comfortable.

[David Kirk]

I've used everything from 175s to 190s. I'm 6'4" with average length legs for my height and as I recall his formula says I should be spinning 200's. I used 190's for a full season and it worked but I never felt "just right" on them and went back to 180's and they just disappear and everything is grand.

The only way to know if a crank length is right for you is to try it, formulas be damned. It takes some time, and money of course, but using them for some period of time is the only way to know how your legs respond.

dave

[AllanVarcoe]

I ran 185's on BMX race/trails/street/skatepark bikes for 20 years and once I got onto a road bike I got so comfortable on 175's that when I go back to my BMX bike I feel like I'm climbing a staircase skipping 3 steps at a time but in 5 minutes I don't even notice it.

I guess what I'm saying is your body will adapt. Whatever feels good should work.

[ripvanrando]

I ran a set of 200 mm cranks for a full season or so based upn Zinn's recommendation. It took a few rides to get used to them and powering up hills was a revelation.

[pavel]

if it was a revelation why did you only have them for one season?

[ripvanrando]

if it was a revelation why did you only have them for one season?

Changed to a different type of riding and different bikes.

Longer cranks need a bike that is designed for them. For instance, the BB needs to be higher.

If you are going low and aero, hip angle is compromised with long cranks compared to a more 'endurance" type riding style and position on the bike.

Or, I just have too many bikes. YMMV

[rockdude]

If you look at research on efficiency you might be inclined to more to a shorter crank.

[Russian bear]

Unfortunately, experimenting with crank length is an expensive affair. I switched from 175s to 170s on the go fast bike and really like the change. Biggest improvement was hip flexor no longer feeling cramped at the top of the pedal stroke and I'm more comfortable in a low position. Cornering clearance improved also.

Reading about crank length, I saw it mentioned that 30 years ago a bike my size would have come with 170mm cranks and 40cm bars. I guess what's old is new again as both of these trends are back.