View Full Version : Crank length question

03-10-2006, 06:20 AM
Does anyone ride two different crank lengths on their various bikes? I've got a 170 on my hybrid commuter but my new road bike (52cm Rocky Mountain Sherpa) has 175s on it. I think that's mighty long for that frame size but I'm willing to ride them if it won't hurt my knees. I notice when I do one-legged stroke exercises that there's a big old dead spot at the top of the stroke, I guess because my leg is not used to pulling up that far.

03-10-2006, 07:16 AM
Does anyone ride two different crank lengths on their various bikes?

My first thought on seeing this question was that you had different crank lengths on the same bike. Maybe for people with one leg shorter than the other it would work? I have 170s on both my bikes. 175 does seem long for that size bike. Your leg length and riding style should figure into crank length.

03-10-2006, 07:18 AM
Crank length is a HUGE issue in the recumbent community right now, with some 6-foot + men going down as low as 153.5's. All sorts of wonderful things are attributed to short cranks; elimination of knee issues, speed gains, whiter teeth, more sex appeal, you name it. Color me sceptical.

The most reasonable theory I've seen is that the crank should be some percentage of your femer length. I'm trying to say 20%. I don't think that's quite it, but that's the ball park.

It sounds to me that 175's are a bit too long for you. The dead spot being the giveaway. I don't know how tall you are, but you might consider going down to 170's or even 165's - especially if you are worried about your knees.

The problem is, of course, that the only real way to find out about these things is to spend the cash and try them on the bike. {sigh}

FWIW, I'm trying to talk DH and my budget into a really expensive new crankset with 165's. I'm looking forward to the increased sex appeal. :)

03-10-2006, 07:33 AM
One of my bikes, which I bought used, has 175 mm crank arms. My other bike has 170 mm arms.

I looked up various charts, and the 175 mm arms are a bit on the long side for me (I'm 5'7" with a ~ 32" inseam).

Call me dim, but I really don't notice that much of a difference.

A few months back I was having a bit of an ache in one knee after 40+ miles, but I noticed that on both bikes. Come to find out the cleat angle on my shoe was a bit off, and adjusting the angle did the trick.

One of these days I'll probably change the crank on Dusty to 170 mm, the length I'm "supposed" to use, but I'm not in a hurry.

03-10-2006, 08:37 AM
I'm looking forward to the increased sex appeal. :)

Oohh, me too! Maybe I'll get whiter teeth too...

Thanks guys. I'm mostly concerned with potential knee issues but I'm about 5'9" (inseam 31.5 - call me Popeye) so, while the 175 is probably too long, it's not outlandishly long. I know a new crank means $$$$$ and I hate to return the bike (I'm within the 30 day return period) because it seems to be perfect in every other way.

03-10-2006, 09:31 AM
Do a alittle research and maybe check with your LBS but 175 cranks are long for your height. You should be on 170's or at the longest 172.5. Yes it seems like the difference is so slight as to be unnoticeable but trust me there are differences and if doing longer rides, you will feel it both in leg fatigue and in performance. Now it's not unusual to have different cranks length on different bikes especially if the bikes are designed differently and used differently but you still need a crank that fits your size.

03-10-2006, 10:01 AM
I read somewhere that people often have longer cranks on their mountain bikes than their road bikes. Not sure if this is the case for most but after reading this I checked and I do. I have 170 on my road bike and 175 on my MTB and both feel just fine.

03-10-2006, 10:46 AM
Interesting you should bring this up about mtn bike cranks. This bike is made by a company that is primarily famous for mountain bikes. They may have decided on 175s for this touring bike because that's what they had a big contract for with all their other models. Hmmmm.....it's a compact geometry frame, too, rather than the traditional frame most makers use with touring bikes.

03-10-2006, 11:29 AM
Hey Nuthatch
Here is where I saw the bit about cranks. Clink on link and then scroll down to the cranks part.

Hope this helps.


03-10-2006, 05:06 PM
Try these sites:




03-14-2006, 04:07 AM
Okay, I put the 175 cranks (with bike attached :p ) to the test this past weekend, with a really windy, fast ride. I spent alot of time watching the disappearing backside of my riding partner!

I just couldn't keep up and I'd like to blame it on a more inefficient pedal stroke because I'm not used to the bigger circles I'm turning with the cranks. Of course, it could be the extra 10 winter pounds on ME, a heavier bike, etc., etc.

I made sure my seat was up as high as it could go without hurting my knees but that put the handlebars way low (ouchie to the neck). What felt good on the first ride (a sedate 12 mph on a quiet day) was all wrong on a challenging ride. So the bike got returned to Performance.

I'm checking out a Novara Randonee now. It's incredibly heavy (28 lbs naked) but I just love the adjustable stem on the bars (neck happy!) and the mountain crank and cassette for those hills.

Of course, I'll STILL be looking at my riding partner's backside! She's riding an 18 pounder! Waaiiitt fooorrr meeee!!! :p :p :p :p

Thanks for all the advice and links!