Crank Length differences....

[RallyMarshal]

Going to sound like a real noob here but since starting back riding Ive had my original Marin and a hack GT Tequesta, both with 175mm cranks (M563 and STX compact chainsets respectively).

The donor bike I used to rebuild the Marin had 170mm cranks and at the ride on the weekend my legs and riding felt "wierd". I thought Id got used to the GT and therefore I just needed to get used to the Marin geometry and riding position but again out riding tonight I really seemed to be spinning the chainset and getting nowhere.

Now am I being stupid - is the difference between a 170mm and 175mm crank noticeable when riding...?

Paul..

 

[Agency_Scum]

Yes. That's why I prefer 180mm cranks. Now watch me get shot down.

 

[tintin40]

I think its more the long term effects on your knee joints. 5mm is a lot. Just moving my seat post a small amount has a big affect.
I've always had 175 as that people of my height should have (Mr average) 5 feet 9 tall 32'' inside leg
But I've never thought of trying any of the other lengths. As 170 for short legs, 180 for long legs?

 

[chaser]

I tried 170's a while ago... could notice the difference from 175's

170's felt like hard work!

Went back to 175's

Hope this helps

 

[FairfaxPat]

I'm 6'1" and I ride 180mm cranks on my MTB, and 175mm cranks on the road, and I can really feel the difference. In the dirt you need torque to get over tough spots, while on the road, with it's even gradients, RPM is more important. If your legs are long enough, use the longer cranks and the tough hills will be easier! Another thing to remember, when you put longer crank arms on your bike, you must LOWER your saddle 1/4" or more to accommodate the larger circle and, at the bottom of the stroke, a pedal that is that much lower to the ground than it was before with the shorter arms.

 

[hamster]

Crank arm length is important for two reasons:
1 Efficient movement of of your leg
2 Gearing effect between crank arm length and chainring size.

For the first you can over- or under-extend your knee. I rode one agonizing tour after swapping from 170s to 175s. I had bad knee pain. So you need to get the right length for your leg.

For the second, the leverage of a longer crank arm will make a given gear combination seem lower as you get more leverage.

 

[RallyMarshal]

Thanks...

Thanks to all of you for your posts - it seems that I wasnt being quite so stupid then!

I understood the concept of leverage dependant on length but 5mm seems such a small amount that I talked myself out of it!

Now to try to source some black 175mm FC-M563 cranks in good condition (or maybe get my old ones anodised or powdercoated)

Paul..

 

[Harryburgundy]

Mmmm...interesting. Noticed the other day that the Deore cranks on the Orange Prestige I bought are 170mm.
Guess I'll try them..or I have some 175 M900's on the way too.

 

[Agency_Scum]

I've 175mm XTs on the tourer, 172.5 Dura Ace on the racer ( my knees would explode on 170mm....my inside leg is 36" ) and I'm getting a set of 1989 180mm cranks for me 29er. Such small differences do sound like piffle and tosh and, indeed, when I've posted on the subject on Single Track World I've had me head proper bitten off by some of the louder-mouthed t0ssers on that site ( I used to love that forum loads, it's getting back to what it used to be though thankfully ).
Here's my take as a proper giraffe; you do notice the difference, I'd suggest mainly if you're a high mileage rider/non car driver. The 180s feel like big-@rsed paddle steamers with bags of torque ( PERFECT for singlespeeding regardless of height ). The 172s and 170s feel like high-geared sports cars that are great at higher speeds but a bit poo in traffic while 175s feel like " mummy bear " just right.

Discuss....

 

[hamster]

As a non-giraffe, 175s are OK on the MTB and singlespeed, 170's for normal road use. Never tried 165's, would probably love 'em.