So, I’m looking at adding a left arm crank power meter to my gravel bike. I use power pedals for road and tri but that’s obviously not good for gravel/cross cycling. I can’t find any GRX crank in stock for 172.5. However, there are plenty of 105 and Ultegra cranks. Will an Ultegra or 105 crank work with my GRX 600 crank set?
I believe they would work.
This place shows 172.5 grx in stock, but I’ve never ordered from them.
https://powermetercity.com/product/stages-shimano-grx-rx810-power-meter/
Aside from crank compatibility, just make sure a stages pm will clear your frame.
Possibly, probably not correctly.
grx will mostly likely be designed around extra clearance away from the chainstay and tyre, so should have more of an offset to it “equivalent Q factorâ€.
A standard 105/ ultegra LH arm won’t have the necessary “out†so it may foul the chainstay, and you may have a funny stance
I’m using a 4iiii Ultegra arm on my GRX bike, works fine. Having said that, this arm didn’t work on the gravel bike I have Ultegra on (3T Exploro). Issue wasn’t the arm per-se, it was the PM box on the back of the crank. Not enough clearance, hit the frame.
On that bike, I had to use an older 105 crank arm, which had more offset.
So… Ultegra will fit on crank, might not fit on bike.
What’s your bike? How wide are the chainstays?
It’s a Wilier Jena. I haven’t even received it yet. Shipping has it coming on Tuesday. So, I haven’t had a chance to check the clearance.
When you get the bike, measure the clearance on the GRX crank. We can calculate from that what will work.
This seems also a good solution, if they start to deliver there products (we are waiting since autumn 2018, when they had there Kickstarter Phase): https://www.iqsquare.com/products/iq2-mtb-powermeter-single
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There is a 1/2" clearance between the inside of the crank arm and the chainstay. Thank you for your help
There is a 1/2" clearance between the inside of the crank arm and the chainstay.
You’ll lose about 5mm of that going from a GRX to an Ultegra arm, which probably puts you inside the 10mm clearance needed for the pm box on the crank arm. It will depend on the shape of the chainstay.
The solution for me was to use a 4IIII mounted on an FC5800 105 arm. Offset is only about 1mm in the area where the PM box is located, but has same Q as an Ultegra and little/no weight difference. As a bonus, they’re also pretty inexpensive if you can find one.
Do you think at 105 7000 will work? or is that the same size as the ultegra?
https://www.clevertraining.com/stages-power-meter-shimano-105-7000
I don’t have to have the power meter immediately and I guess I could just wait for GRX cranks to go back in stock. I found a grey one on Jenson USA, but I think one grey are and one black arm would look way worse than a black GRX and a black 105.
The 172.5 is out of stock there. The other lengths are available. 
Jenson shows 172.5 in stock
https://www.jensonusa.com/Stages-Power-L-Shimano-GRX-RX810
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Yeah, I saw that, but it says that it is a grey crank arm and the rest of my group set is black. That might be a little vain, but I would prefer the colors at least match.
You can put an xpeedo mtb pedal body on favero assioma pedals, great option for gravel. My brother uses the assiomas like this and he loves them.
Do you think at 105 7000 will work? or is that the same size as the ultegra?
I don’t know, sorry.
Competitive Cyclist says it will work. Bonus that it’s almost $100 cheaper than a grx crank with DCRAINMAKER code. So, I went for it. I’ll give it a go and report back in case anyone else runs into this problem too.
UPDATE; 105 did not work (pod was rubbing against chainstay) even though Competitive Cyclist said it would work. However, they fully refunded me and now have a grx800 crank 4iiiii meter in stock. So, I ordered that and am just waiting.
Even though I wrench on my bikes, I run these sort of things against the pros at the LBS. Too many BB and crank ‘standards’ vs power meter compatibility.
Even though I wrench on my bikes, I run these sort of things against the pros at the LBS. Too many BB and crank ‘standards’ vs power meter compatibility.I agree. The GRX crank has a chainline that sits 2.5mm further out than Shimano’s road groups. Why? To ask the question another way, if they want chainstay tire clearance why don’t gravel bikes just go with mountain bike chainline and BB standards? I’ll tell you why: to force people to buy new stuff. Shimano makes great stuff, but they are the kings of this kind of total lack of cross-compatibility.