I'm in the process of ordering my new bike. The bike is a 53CM frame, they said the crank is a 175mm crank arm which they're out of. They said they could do a 170mm or a 172.5mm crank arm. How important or difference is the 175mm oppose to the 172.5mm crank arm? I know the longer the arm, the more leverage for more torque just as in a longer stroke engine, and the shorter the arm the faster RPM. Can someone give me advise on this. I'm not using the bike for no Tour DeFrance, just some long recreation riding.


Thanks

You may want to check out some recent discussions on this topic.

• Tire Smoking Torque...Let's discuss this
• A word of wisdom....
• Crank Arm Length

I'm surprised that your order would be a 53cm frame with 175mm crank. I would expect a 170mm crank on a 53cm frame. Usually the crank length is proportional to the frame size. Leverage is one thing. Being able to spin the thing is another all together. If you fit a 53, you will probably be happier with a shorter than 175cm crank.

Yea, I did a search and didn't come up with anything defining the actual formula to get the size I needed. I’m 5'9" my crotch to the ground is 31.5" or 80cm. The gear I'm going with is a triple 30-42-52, 12-25. Is there some sort of a formula to find the correct arm? I'm trying to do as much research as possible before finalizing this order to make sure I get everything correct.

Thanks

Let me ask you a quick question. Do you feel like you have short legs for your height? The reason I ask is because 31.5 inches sounds more to me like a pants inseam length than a bicycling inseam length for somebody who is 5'9".

Assuming the inseam thing is correct, my feeling is that 175mm crankarms for a road bike would be a little bit on the long side. If it was for my bike, I'd go with 172.5mm.

I was going to say the same thing. I am 5'10" with a 32" inseam and on my Salsa project decided to go with a 172.5 crank rather than the 175 that is on my current bike. I have been talking crank length with my father as weel as he is trying to buy a new bike and he (although just a bit shorter than I) is going to go the opposite wat, from 172.5 to 175. His comment on it was that even in HS when he ran track he always has a long stride and that the longer crank on a couple of test bikes just felt better to him. I had never heard this topic discussed in those terms and it added some validity to my choice of shorter cranks as I know that I prefer a shorter running stride and spinning on a bike.