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Advice on crank length(7 posts)

Advice on crank lengthcoaster
Jan 26, 2003 9:10 PM
My current bike has a 53cm frame and came stock with 170 cranks. I'm building up a new race bike and realise that longer cranks suit my style... I'm a big gear pusher/sprinter, and I'm no spinner. My MTB is has 175's and I've tried them on a road bike before and they seem pretty good. Is that too long??? Should I go with 172.5 instead? Thanks.
an interesting site.croll-duraace
Jan 26, 2003 9:29 PM
I was doing a little research on the same subject myself about 6 months ago...hope it helps.
re: Advice on crank lengthhfc
Jan 27, 2003 7:19 AM
I recently did some research myself about a month ago using the website mentioned in the other reply. I found it through a google search and it was very detailed. Unfortunately it's been renamed or something. The upshot of it was that many people, especially tall ones, need longer crank lengths than what is commonly available, usually in the order of 180 to 190 mm. Based on your frame size you're probably OK with the 175's provided your knees or hips/butt don't hurt on long rides. Another thing I learned is that small increment changes (like 2.5 mm) don't make much difference. I got a bike with 172.5 cranks and was debating a change to 175. I decided to stick with the 172.5 based on that info.
re: Advice on crank lengthatpjunkie
Jan 27, 2003 11:59 AM
I'd say if you plan on doing any crits go 172.5, you'll appreciate the ground clearance.
Now hold on a minute!Kerry
Jan 27, 2003 6:00 PM
It is generally the case that longer cranks make it harder to spin, and high cadence is the best way to minimize knee problems.

Every increment of crank length is about 2-3 rpm. Going from 170 to 175 is about 5 rpm. Spinning is more physiologically efficient, all else equal. It is also something you have to practice - you can't say "I can't spin" unless you have spent some serious time working on it, day after day over a season or two. The primary disadvantages to low cadence like you use are 1) harder to accelerate quickly starting from a lower cadence, 2) you'll have less left late in a ride, 3) risk of knee problems, and 4) you have less "turndown ratio" in your gears. If your total range of cadence is 50-60 up a steep hill to 80 on the flats, you need to have a wider range of gears to get you everywhere you want to go. If you can comfortably spin up to 110, then you can go 35 in a 53/13. If 80 is your comfortable cadence, you need a 53/11 to just go 30.

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. What little research has been done on crank length suggests that people adapt to different crank lengths and there is no optimum or formula related to body proportion. 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.

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 be masked by the effects of weather, fatigue, and the placebo effect of riding on "faster" equipment.
Reduced to basic physics,micha
Jan 27, 2003 7:00 PM
crank length is this: longer cranks give you more leverage at the price of a larger circumference of the pedaling circle. Using basic torque arithmetic (assuming we're pedaling circles and generating torque, not just downward force), a trained cyclist able to pedal such circles gains nothing with longer cranks in general road racing.

However, if you're a dude trundling down to the local pub on your one-speed 40-pound coaster brake special stomping the pedals from 1 to 3 o'clock at a 30 rpm cadence, longer cranks will definitely help you out.

In the real world, the best crank length is probably the one you've been using comfortably for the last few years. The body adapts, marvelously. In my opinion, changing crank length from your norm will slow you down for at least three months, and most probably not make you any faster after that.
re: Advice on crank lengthmaximum15
Jan 28, 2003 9:39 AM
I have to agree with the "if it feels right" and "the body adapts" advice. My first road bike (3 years old) had 175mm cranks. When I got that bike, I didn't even know cranks came in different lenghts. Recently, I picked up an old Bianchi with 167.5mm cranks. I love the Bianchi and it rides fine, but I am changing the cranks to 175mm because I can tell the difference in the crank length. It isn't uncomfortable, it just feels different and I notice it. There is no difference in my cadance or speed with the two bikes, just a different feel while pedaling and I like the one I am most used to.