MTB crank q-factor

[FishMan]

Does anyone know where/how I can find out the q-factor of various MTB cranks (other then the obvious that would be to knock people off their bikes and measure the q-factor and run away)?

I have a "old" set of LX M571 cranks on my touring bike and the pedals are just too far apart for the big road miles that bike gets. Would a new set of XT cranks have a lower q-factor? I'm thinking something narrower would be a lot more comfortable, and maybe more efficient too? Plus I wouldn't mind a larger big ring (currently only a 42), the whole lighter weight and stiffer thing would just be icing on the cake.

Anyone know a good place to find this info?

[rockyrider]

DanO on MTBR.COM posted a good chart of Shimano cranks Q factors.

[markie]

The Q-factor may be be influenced by the bike.

If it has wide stays for big tyres you may need a big Q factor for the cranks to clear the stays.

If you have square taper cranks and they clear the stay by more than 1cm you could just put in a slightly shorter BB spindle... You need to keep at least 5-8mm between the crank and the stays.


(unless you run one gear in which case it'll screw you chainline)

[Goride]

The new outboard bearing systems are "almost definitely" wider than cranks of old.

For years manufacturers were worried about q-factor, telling everyone it was a biomech and efficiency thing, and then threw all of that common knowledge away with some outboard systems... All to solve the problem of people jumping off rooftops and breaking bb axles. Which few of us actually do.

[rockyrider]

...and then they added 85 and 100mm wide BB shells to make it even harder to pedal a motocross (err.... downhill) bike without the motor.

MTB cranks are about 20-30mm wider Q-factor than road bikes just to get the crank arms to clear the chainstays.

[TheCrazyFinn]

The new outboard bearing systems are "almost definitely" wider than cranks of old.

For years manufacturers were worried about q-factor, telling everyone it was a biomech and efficiency thing, and then threw all of that common knowledge away with some outboard systems... All to solve the problem of people jumping off rooftops and breaking bb axles. Which few of us actually do.

Actually, the outside bearing designs were to solve the fact that non-outside bearing spline-drive BB's eat bearings for lunch. Spline-Drive BB's were invented partially to solve the broken-axle issue (which is definitely a serious problem with square-taper BB's on DH bikes) and partially to allow vendor lock-in on BB sales and prevent bikes being spec'd with cheapo BB's and bling-bling cranks(sadly common in the mid/late 90's). Unfortunatly ISIS came along and allowed that again (as long as the cranks aren't Shimano).