Road Cycling - 170 to 175 or 177.5mm cranks

Hi all.

I have Dura ace 9 speed with 170 mm cranks. I want to upgrade to 175 or 177.5 for a bit more leverage for climbing. The guy at the LBS was saying that I may be a bit short for the 175 or the 177.5 cranks. I am 180cm (5 feet 11 inches) tall so I don’t think I am that short. He was also saying that I might get sore knees from the longer cranks.

The advise to get 175 or 177.5 mm cranks comes from an old pro cyclist so I thought I would try them out. do you think there is much of a difference between the 170 to the 175 or the 177.5??

Thanks
Slick1

http://www.peterwhitecycles.com/fitting.htm

scroll down to Cranks, read up before doing anything. Ya don't wanna screw up them knees!

Thanks to Murray for getting me that link.

Personally, I went from 172.5 to 170 and found that I climb much better with the shorter crankarm. Now instead of mashing bigger gears, I tend to spin at a much higher cadence in a smaller gear. I was very nervous about making the change at first but now I am extremely glad I did.

I don't mean to confuse your decision, just thought you might find my experience relevant.

What's your inseam? 33"? Use 175's. I like 5.3 mm of crankarm length per inch of inseam, so 33 X 5.3 = 174.9mm. Find Lennard Zinn's website, and you will see he likes to go a little longer than that. There is absolutely no point to having long legs and taking short steps, and that is what you are doing with short cranks. It makes a difference and you will do better with longer cranks.

The above is a rule for road cycling and it is cadence specific. Optimal crankarm length does vary with cadence, getting shorter with higher cadence, which explains the longer cranks used by MTBers, and the shorter cranks used by trackies, relative to optimal length for road cycling.

If you exceed the normal range of motion with loaded knee joints, you can injure them, but I often wonder what the consequences of the enormous loads applied to excessively short crankarms might be as well.

With a 35 inch inseam I use 185mm cranks, and I have been doing so for more than 10 years with no ill effects, and to advantage.

I fail to see how putting longer cranks on a bike could damage your knees. It's not like you'd go to longer cranks and not then adjust your position ( unless you were an idiot ). If your position is right, it's right whether you're running 175 or 170mm cranks, and adding 10mm to the circular motion for turning the pedals could not possibly be out of anyones 'range of motion'.

I have a 36.5" inseam and run 177.5 on the road and 180 off road. I'd love to go longer. Everything in proportion is my motto.

I'm 175cm tall with 85cm inseam and I switched from 170mm to 175mm cranks a couple of years ago and will not switch back. I don't seem to be able to spin the longer cranks as fast on steep downhills or in sprints, but I don't race so that's not a big concern for me.

o.k. so i think i'm set on 175 cranks.

My next question is do you notice a difference in performance in climbing??

thanks
slick1

The places you notice the difference the most is in climbing and in full-power sprinting.

I fail to see how putting longer cranks on a bike could damage your knees. It's not like you'd go to longer cranks and not then adjust your position ( unless you were an idiot ). If your position is right, it's right whether you're running 175 or 170mm cranks, and adding 10mm to the circular motion for turning the pedals could not possibly be out of anyones 'range of motion'.

I have a 36.5" inseam and run 177.5 on the road and 180 off road. I'd love to go longer. Everything in proportion is my motto.

it could damage your knees b/c you would be moving through a larger range of motion. if you dont have the necessary flexiblity you could hurt yourself. as a rule, your knees shouldn't bend more then 90 degrees. just my two cents. FWIW, thylacine, your probably ok...but for the short guy, I dunno...

<..do you notice a difference in performance in climbing??>

Yes, absolutely. I went from 170s to 175s (I have an 82cm inseam) and knocked 20 seconds off a 7 minute climb in my 39x23 with a cadence of about 80 and not trying too hard. Didn't change anything else, have no problems (first couple of rides I got a little sore in the shins and calf muscles) and can still spin high cadences. It no longer feels like I'm going up stairs that are too short.

Go for it!

The places you notice the difference the most is in climbing and in full-power sprinting.

after 10 years, I switched from 172.5s to 170s. longer arms are good for torque on steep hills and leverage to get going, but after the firs couple of turns and you get up to speed, I don't think you get much benefit from longer arms. I know lennard zinn has been an advocate for longer cranks, but he's a tall guy. I'm 5'8 and as I got older, I noticed that my leg speed has slowed. With shorter cranks, I also went to a compact crank and my leg speed has gone up and I think my climbing has also improved. I think a smaller circle allows for smoother pedal strokes. But if your leg length is long enough, 175s might be just right. be sure to lower your seat and check the position of your foot over the pedal.

let us know how it goes. :)

The places you notice the difference the most is in climbing and in full-power sprinting.

o.k i think the longer cranks it is. my next decision is whether i should go for the 175 or the 177.5? any suggestions??

o.k i think the longer cranks it is. my next decision is whether i should go for the 175 or the 177.5? any suggestions??

If you are set and sure about jumping to either 175 or 177.5, then definitely go with 175. I think 170 to 175 is a big jump. Personally I would recommend the change to 172.5 and see how that feels.

I just went to a 172.5 from a 170 and I have noticed that my cadence is much slower, and my knees hurt.
After reading this thead I will be going back to my beloved square taper shimano 600s. Look for a set of Ultegras with a bottom bracket on Ebay soon.

Well I went from 170 to 172.5 and noticed very little differance in climbing or cadence, the differance is not much in the scheme of things. For most people I don't see why it would slow down your pedal speed or make someones knees hurt unless you forgot to change seat position.

I notice that I am able to stay on the big ring more going up inclines, I may give it more time . I have only done about 75miles with the 172.5. Maybe I am mashing more because of the leverage but 2.5 mm should not be that big of a difference.