Exploring putting XT L/S crank arm (with power meter) on Ultegra crank.

This would offset L/S 12mm more than R/S. I could add 20mm pedal extender to R/S, this would leave R/S 8mm wider

Any experiences dealing with off set Q- factor like that?

I have read on another post that 6mm on some bikes out of box is normal.

thanks in advance

Different for different people but for some 12mm would be a huge difference and could be enough to ruin hips and knees etc. over a long enough period of time. At a minimum most will likely notice the difference in offset of a few mm but again it depends on the person. As an example I'm in my mid 50's and the older I get the more important the perfect Q-factor becomes. I find that over 1mm of offset in either direction will cause some knee pain before I even ride 5 miles. When I was younger, not so much, but even then over 5mm off was noticeable. Best to try it yourself to get the answer you need.

I think a 12 mm offset would be very noticeable. Can you change the entire crank to get it closer to symmetrical again?

Thanks for your responses! I could get proper Ultegra crank arm with power meter, but just trying to save money ($800 for crank w/power meter in it). I would still need to obtain Ultegra crank @ 175mm to match MTB crank length


I am considering investing in a "Stages Crank Arm" Power Meter https://www.stagescycling.com/stagespower-models

Being on a budget (I guess who isn't), I am exploring buying the XT w/power meter in it and being able to make it work on my CX/road bike.

It will not work the other way - Ultegra arm on XT crank (not enough clearance for power sensing unit) https://www.stagescycling.com/support-compatibility

While 12mm is far more than desirable, it may not be an issue for a big guy. Putting it in perspective, it's the same as the saddle being off by 6mm or about 1/4". I've seen leather saddles with offset wear patterns more than that. Also consider that 1/4" over 30" or so of leg length boils down to less than 1/2°.

People get worked up over Q-factor and offset cranks, but there's nothing to say that pedals are directly below the hips anyway, and I've yet to hear of anyone adjusting Q-factors according to hip width.

So while you may notice, I'm not sure you will, or at least that you would have if you didn't know. Build it as is and see how it rides. There's little or no risk of adverse consequences, but if you think you feel a difference, you can cross that bridge if/when you get to it.

Although I've never tried it, I think a 12mm offset would be horrible. Adding 12mm to each side with a pedal extender? That sounds worse. A while back I rode a spinning bike with a large q-factor (didn't measure it) and hated it.

Pfft. Then skip the power meter and just ride more

looking in old Campag catalog, back when crank-arms were at right-angles to the BB spindles.

left commonly 16~17mm, right side equal only on 120 track frames and hubs. 68-P-120, 70-P-120

or 65-P-110.. both narrower..

I see your point on wider q-factor.

But, after you mentioned it i measured q of cx bike vs mtb. Mtb is a little over 1" wider @ 7" while cx bike is a little under 6". I couldn't believe the differrnce & double/triple checked it. I never noticed the difference going on 2hr+ bikes including 300 mile road tour on cx bike

As I said, if the object of narrow Q-factor is to get pedals below the hips, then optimum Q-factor depends on the width of the hips.

Thanks for your response.

I apologize, but i am not familiar with the terminology.

Are you saying that @ one point, an offset "q" was somewhat normal? If so, what was difference in offset?

Thanks in advance!

Offset Q-factor is about as old as chain drive. Nobody ever thought about it much. Even on modern bikes with BB30 or external cups, the cranks are attached at a set distance from each other, and chainline may be changed by moving spacers, which can create offset Q.

It's just that 12mm is well above typical, so may be noticeable, and then again may not. This is why I suggest completing the build and riding. You can cross the offset bridge if or when you come to it.

My rule No.17 of basic bike mechanics is that any perceived or theoretical "problem" that doesn't manifest as one when riding, isn't one. Ride performance trumps all measurements.

BTW- who's the brainchild who decided to make the number/pound symbol into a hash tag?

Q is the pedal to pedal width.. right hand angle cranks win on that ,

the 65-P-110 spindle in a track bike with a 65mm width BB shell , and 110 wide rear fork,and hub.

would be about as narrow a Q Crank As I can imagine..

to use 2 chainrings and 5 cogs in the back the Right end crank has to move outward ..

Modern cranksets no longer have straight crankarms, so the Q cannot be as narrow, but the way
the crankarm is designed has let the BB spindles be shortened. and the bend arms shapes
are less likely to hit your ankle bone on the end of the Arm..

Not sure what you mean by all that. I have SRAM GXP and BB30 cranks. The spacing between the pedals is the same, though on the narrower BB30 the arms angle inward from the pedals toward the hub whereas on the GXP crank the arms are more straight and parallel to the longitudinal axis of the bike. If it was deemed desirable by SRAM, the BB30 pedals could easily be 3-4 cm closer together.

Agree with FBinNY that 1 cm offset is going to be unnoticeable and inconsequential.

#it'scoolandtrendynowyoucrabbyoldfart

Crabby and old, yes. But an old fart?, No, at least not yet.

You can put a 2.5mm spacer behind the DS bearing cup (which come with many MTB BBs to allow installation in 68mm BBs instead of 73mm), and you should still have plenty of axle sticking out of the NDS to attach the HTII crank to. I've done this to tweak the chainline on one of my bikes (105, 5600 crankarms on both sides), and have had no problems after 4000+ kms. You can also add a couple of pedal washers behind the right-hand pedal, and still have plenty of thread engagement (on my setup, I put these behind the left-side to compensate for the BB spacer). Doing both of those things should move the RH pedal out by about 5mm, which is hopefully enough to make the offset not noticeable.

I intentionally increase my Q-factor like 18-20mm on each side (I forget the exact size of my pedal extenders), because I have duck feet (out-turned; opposite of pigeon-toed), and if I force my feet to be straight forward like a 'normal person' I get terrible IT-band pain. And without extenders, if I allow a natural foot angle, my heels hit the cranks every single revolution.

First time I put the extenders on I felt "WHOA this is different", but adapted very quickly and now it feels normal and my pain is gone.

So yes, radical increase of Q-factor may well cause pain and/or injury, or it may also (as in my case) prevent it. Depends on the individual body.

Thanks! The excellant advice I was looking for!

The 2.5mm spacer - Looking at my mtb with XT that is the black plastic one you would slide on to crank shaft before sliding into BB -right? Then adjust front derailleur accordingly?

Yep, that would be the one.

I just went downstairs and measured a couple of older bikes with square taper BB's. The Trek 330 double was 2 mm farther on the drive side; the Cignal Tandem triple was 7 mm farther on the drive side. Neither I nor anyone else who has ridden either has ever commented that it felt odd. (It is too cold and wet to go out to the garage to measure my more modern bikes.) The human body is pretty adaptable, and is also not exactly symmetric. I would vote for trying it and seeing how it feels before jumping through a lot of hoops to get something symmetric which is probably not so on many bikes.

Good stuff! Thank you!