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170 vs 175 cranks(3 posts)

170 vs 175 cranksSpeedy
Aug 11, 2001 7:49 PM
I am relatively new to cycling.

I have been running 170 cranks for 30 - 40km races (Cycle prtion of run, bike, run Duathlons).

Someone suggested that I run 175 cranks for racing as opposed to 170's.
If I did this, what improvements over the 30 - 40km distances can I expect if any?

Thank you,
re: 170 vs 175 cranksBirddog
Aug 12, 2001 7:12 AM
That's a good question. You might not experience any improvement, or worse yet, you might have poor results. Tri heads think that with the longer crank arms and resultant slower foot speed, you will develop more power and speed per stroke. Personally, (I used to be a tri head until therapy cured me of my OCD) I found that 172.5 was ideal for me. I'm naturally more of a spinner than a grinder and I simply had faster times both on and off the bike with this set-up. I succumbed to the lure of a great deal on some super lightweight 175 cranks and with the knowledge that they would make me faster (according to conventional tri head wisdom) I bought. I was never as fast as with 172.5's and after a year of mediocre results, returned to my shorter, heavier cranks, and improved once again. It is a personal thing, and your results could vary. The big question is what size would you use if you were strictly a Roadie? Start there in my opinion. I rode 170's for years before finding that 172.5 was my optimum. I didn't know any better, they came with the bike.
The short answerKerry Irons
Aug 12, 2001 11:26 AM
You will find no high quality data to support any particular crank length as being better than any other. This is true whether or not you correct for leg length, femur length, etc. On the other hand, you will find lots of anecdotal or low quality data to support all kinds of conclusions, and more theories than you can shake a stick at. A rider's response to changes in crank length is 1) highly individual, 2) dependent on riding style and the event (TT, climbing, crits, track racing, etc.), and 3) most important, highly adaptive. This is why it is so hard to study the effect of crank length.

So the short answer is: if it feels better and measures faster, do it. If it doesn't feel better but measures faster, maybe you should do it and hope to adapt. And even if it doesn't measure faster, you may adapt and get faster. Simple, eh? NOTE: measures faster means repeat timed distances on different days in different weather, not just "faster on my nightly ride" which can mask the effects of weather, fatigue, and the placebo effect of riding on "faster" equipment.