165mm cranks ?

Dogboywonder

Dogboywonder

Member
I know folks preach about the leverage that comes w longer cranks but I was wondering what folks thought about 165s for MTB. I’ve got 165s on my cross and road bike. I love them. I have a crazy leg length discrepancy and the switch has done wonders for my knee on the longer leg
 
Jmann

Jmann

Never gonna let you down.
For years I’ve been wishing they spec’d mtb bikes with shorter cranks. Not for performance but more for clearance and rock strikes. It seems now they are moving from 175 to 170.
Personally I think longer cranks work best with consistent efforts like tt. Mtb is often on/off power, quick accelerations in cadence. So for that reason I don’t think there’s anything wrong with shorter cranks. If they work for you don’t worry that your missing out on a performance benefit, your probably fine.
 
Patrick

Patrick

Overthinking the draft from the basement already
Staff member
if the cranks were shorter, could they lower the bb?

mechanical advantage goes down, but could make that up with a smaller chainring...
 
SmooveP

SmooveP

Well-Known Member
There are some detailed discussions about this on MTBR that I read awhile back. A lot of it had to do with the trend toward lower bottom brackets and pedal strikes, but there were some links to studies and what the "optimal" crank length is for a given leg length. 5mm is a pretty small difference, and so is 10mm really. If a shorter crank solves your knee pain issue, it sounds like a no-brainer. The hard part might be finding 165mm cranks that work with your bike.
 
jklett

jklett

Well-Known Member
I went to 165 on my hardtail, it feels much better to me and my average cadence went up. I was on 175's before that and was having some pain issues. I probably could have just cut the difference at 170 and it would have been fine but I didn't think that small of a change would make any difference(although my other bikes all have 170's and I don't have any pain with them). I'm also 5'6" with stumpy legs so take that into consideration.
 
Xler8

Xler8

Well-Known Member
175 was all I ever run, however with this last build I got a pair of 165’s and it’s pretty damn good. So good I may switch all the bikes...

I can envision a larger leverage ratio with longer arms, but in all reality the 10mm difference is barely noticeable as far as power to the rear wheel.
 
one piece crank

one piece crank

Well-Known Member
I’ve been thinking of putting 165’s on my fun bike. I don’t expect much difference going from 175 to 170, especially with the change from SS to 1x11, so it looks like 165 is worth a test.

EDIT: I'll add that my play bike is really small, and I'm pretty tall (6'4"), so there are fit dynamics in play. The old SS config and my riding style benefit from a long crank length, but now that it's going 1x11, shorter cranks feel like a good idea (to me). I'm not looking to win races, but to ride things I can't walk (kind of a long distance capable Trials bike). It's a total re-make with new bar/stem positioning and bigger wheels.
 
Last edited:
Magic

Magic

Formerly 1sh0t1b33r
Team MTBNJ Halter's
Whatever works for your knees. Taller people may need to go longer just for proper bike fit, so always make sure your bike is also properly sized as well. I run 172.5 on road and cross, and 175 on the MTB's. I think I like 170 cranks on the MTB more though, but the saddle height would need to be higher. Also, cranks are expensive to swap out for sizing. My fiance has longer legs than me, but shorter arms. For her, a slightly smaller frame than mine with the 175mm cranks is optimal. This way her knees are in a good spot with the plumb bob test for saddle position, lower center of gravity sitting down, and the reach is slightly shorter than my bikes.
 
Ian F

Ian F

Well-Known Member
165mm cranks are essentially standard on DH bikes due to the low bottom brackets and high sag numbers. I've run 165's on my DH bikes since the 90's. Even with 165mm cranks, I still get a lot of pedal strikes.

Otherwise, for bikes designed for pedaling, crank length is usually determined by leg length - shorter for short folks, long for tall folks. 175mm is a pretty typical compromise between torque length, clearance and being spin-friendly. I remember running 180mm cranks on my old single speed bike to get a bit more torque, but I don't know if that is still a common thing today (me knees and single speeds don't get along). I run 172.5 on my road bike as I'm usually trying to spin more than I do on a mtn bike.

Personally, I see no benefit at all to running shorter cranks on a trail bike or enduro bike. Especially not a hardtail. That said, from my previous DH racing experience on a super-low bottom-bracket bike, pedal strikes don't bother me. I get a few on pretty much every ride. Somehow I usually ride through them.
 
stb222

stb222

Love Drunk
Jerk Squad
Ian F said:
165mm cranks are essentially standard on DH bikes due to the low bottom brackets and high sag numbers. I've run 165's on my DH bikes since the 90's. Even with 165mm cranks, I still get a lot of pedal strikes.

Otherwise, for bikes designed for pedaling, crank length is usually determined by leg length - shorter for short folks, long for tall folks. 175mm is a pretty typical compromise between torque length, clearance and being spin-friendly. I remember running 180mm cranks on my old single speed bike to get a bit more torque, but I don't know if that is still a common thing today (me knees and single speeds don't get along). I run 172.5 on my road bike as I'm usually trying to spin more than I do on a mtn bike.

Personally, I see no benefit at all to running shorter cranks on a trail bike or enduro bike. Especially not a hardtail. That said, from my previous DH racing experience on a super-low bottom-bracket bike, pedal strikes don't bother me. I get a few on pretty much every ride. Somehow I usually ride through them.
Click to expand...
Supposedly there are studies that show that crank length doesn’t apply for leverage and like you said, is more of a fit thing. On leverage, based on everything we learn elsewhere, science disagrees, so who knows.

I
 
Ian F

Ian F

Well-Known Member
I remember 180mm cranks were a thing on BMX bikes way back when, but after a quick browsing of some Pro-level race bikes currently for retail sale, it looks like 175mm is now the norm. I'll have to do some searching for those crank length studies. Maybe it doesn't make as much of a difference as one would think, but it seems counter-intuitive that it wouldn't make any difference at all.
 
You must log in or register to reply here.
Top Bottom