GRX Cranksets and XT left arm

 I would like to get a GRX crank and use my left Stages XT power meter with it.  I've found I can't use the XT arm with a road crankset, the width of the XT arm is 5mm wider than that of the Shimano road cranks and the bolt won't reach the interior of the spindle.  Anyone know if the GRX cranks are sized like road or mountain cranks?  Thanks.

GRX are based on the Shimano road groupsets.

Bummer, thanks.

Their factory install program is pretty fast, and not too expensive if you can live without that GRX crank arm for a couple weeks.

GRX cranks are 5mm wider than road cranks to allow for more tire clearance (Q factor is 151mm vs. 146mm), but MTB cranks are usually in the 170 range aren't they? 

So even if you could mount the left crank arm, it would stick out quite a bit more than the right crank arm, and inevitably cause your left knee to explode, or potentially some less severe bike fit issue, or it would work fine and you wouldn't notice.

JWB475 wrote:GRX cranks are 5mm wider than road cranks to allow for more tire clearance (Q factor is 151mm vs. 146mm), but MTB cranks are usually in the 170 range aren't they? 

So even if you could mount the left crank arm, it would stick out quite a bit more than the right crank arm, and inevitably cause your left knee to explode, or potentially some less severe bike fit issue, or it would work fine and you wouldn't notice.

The width (thickness) of my XT crank where it attaches to the spindle is 27.6mm.  The width of the Tiagra crankarm where it attaches to the spindle is 22.4mm.  I did mount the XT crankarm to the Tiagra crank with a DIY bolt and rode it for a while. I stripped the threads of my DIY bolt, so I gave that up. I have been thinking of trying to get a longer version of the Shimano crankarm bolt 3D printed.  I really only need 1 or 2 mm to get it to thread.

Different Q factors don't seem to bother me.  I ride road bikes, mountain bikes and fat bikes and notice no difference between them even though the Q factor varies greatly.  Additionally, I swap the 175 XT crankarm onto a bike that has a 172.5 arm on the other side.  I don't notice the 2.5 mm difference, even on long rides.  My body is not sensitive to those kind of changes, especially on mountain or gravel bikes where you're moving around a whole lot more than a road bike (or at least I am).

I prefer a wider Q-factor and use ISSI SPD pedals with a long spidle. 

You could probably make the XT crankset chainline work in a 1x configuration, but it sounds like your bike is a 2x?

Yes, 2x.  I'm not wild about 1x for gravel, I can't get enough low end for my fat butt and have any top end!