jae33w

Hi all, I have just bought a set of 170mm cranks. Friends tell me that there will be a noticable difference between my old 175's and these. Can anyone tell me if this is really the case, and what are the differences besides length? thanks!

Jim311

Length is not an issue. Or at least that's what everyone else tells me.. I wouldn't really know!

PeterG1185

More lenght=more leverage on the cranks. It can make a differance. Downhillers tend to use longish crank arms for that very reason. I haven't actually ridden a 175 to a 170 so i'm just goin on what i have read. For XC i dont think it'll make that big of a differance.

MichaelW

You should chose cranks based on your leg (or femur) length. Longer legs need longer cranks. People have quite a wide tolerance for different sizes, but its not efficient for big guys to pedal short cranks, or for short riders to struggle with long cranks.
170mm are std for a medium sized guy on a road bike. MTBers sometimes pick a slightly longer size, to get more torque. This may help when you are pedalling slowly, if slow pedalling is what you do.
When you compare 2 different crank length, you really should be using them under the same riding conditions in different cog combinations. The shorter crank is turned more quickly in a lower gear.

The pros of a shorter crank are more pedal clearance over rocks and for cornering. You need to adjust you saddle height and layback to compensate for the 5mm difference.

Maelstrom 

The benefit of shorter cranks is more clearance over rocks so some mtbers go with short just to make it over stunts

tFUnK

maybe it's just me but i find 175 better to grind uphill than my 170 did.

BurlySurly

yes, of course lenth makes a difference.

Most the DHers i know use shorter cranks so they dont bash them on rocks and die during speed runs. The longer they are, the more likely they are to hit the ground. However, the longer they are, the more leverage you have. Its a tradeoff really.

a2psyklnut

The longer the crank the more leverage, so Yes, a 175 will have more power than a 170.

Many single speeders use 180mm cranks, and I've seen some use 185.

The irony is that a lot of BMXers are using longer cranks for more power down the first straight. This doesn't really make sense to me. A BMX race is basically a sprint, jump, turn, sprint,jump, jump, turn, sprint, rythm section, spring, turn, sprint! A shorter cranks that allows you to spin faster makes more sense to me! However, the standard is now closer to 180. Why? Well, cuz that's what the AA Pro's use! Forget the fact that the AA Pro's are all grown adults, and your kid needs a 160mm crank because he's 8 years old! Rant Over!

mtbkanata

I have shorter cranks on my DH than on my XC, and the only time I can tell the difference, is when I stand to climb. Other that that, my seat is so different on each, that my pedal stroke is messed up anyway... I find that any real advantage or disadvantage can be made up by riding with folks faster/better than you are... then you work harder!

Joe

MichaelW

"The longer the crank the more leverage, so Yes, a 175 will have more power than a 170."
Crank length does not increase or decrease the amount of power the rider produces. It increases torque, and/or reduces the force neccessary to turn a particular gear.
To turn a long crank 1rev takes more work than to rotate a shorter crank.