Hello
The q factor seems a bit of a mystery to me. Here goes….

I understand the q factor relates to crank width
I understand that it has a direct bearing on chain line, and if you are running a single speed then thats really important
My question is, why is it relevant to a 2×10 setup for example, where the chain line will almost always be out of line

The Sram x0 crankset comes as 156 and 164 q factor on a 2×10
http://www.competitivecyclist.com/truvativ-xx-bb30-crankset-164-q-factor

I have a Niner Air Carbon that i’m about to build up so any explanation, advice would be appreciated

Thanks
Andy

Q factor is distance between the pedals and has nothing to do with chain line.

And the 156 is bloody narrow, plenty of frames have chain stay clearance issues.

Just buy the wider stance, I have yet to find a frame that the narrower stance fits properly.

On both chainsets the rings are in the same position, same chain line

Q factor has always been an odd one (thank you Tom Richey). there seems to be an idea that narrow is more aero and better but mechanically, shouldn’t you try to keep ankles under knees, under hips?

I think if people worried about it, more would be trying to space pedals out rather than in.

Which is just what Cav does – he has longer axles to space them out.

Depends on your hips and that. I’ve never given it a second thought frankly particularly, particularly on the MTB where you’re moving constantly.

Niner air carbon fits both 156 and 166mm SRAM cranks.

Personally I prefer lower q-factor, but it isn’t something most riders think about or think about changing.
It is mostly related to hip width as above.

I got a fatbike a year ago. The q factor is over an inch wider than my full suspension bike due to the 100 mm BB shell. I can’t say that it causes any problems, or that I even notice it. I just get on and ride…