GRX 46-30 crank with R8000 11-32 + GS derailleur

[sennder]

Hello!

I'm preparing my Trek Domane for an upcoming ride -- 30km with 1800m of elevation.

I'm currently running an R8000 50-34 crankset with a 11-32 cassette and a GS rear derailleur. I'm thinking of getting the RX600-11 46-30 crankset for the ride with the idea that it'll replace the subpar FSA crankset on my gravel bike after the ride.

Has anyone used the GRX cranksets with shimano road groupsets? Would appreciate any insights.

[citrusparty]

Shimano recommend a GRX front mech because the chain line is further outboard on GRX. The chain line is 43.5 for road groups vs 46.9mm for GRX

[pdlpsher1]

The chainline can be corrected using chainring bolt spacers (https://www.ebay.com/itm/402897055805). But I have never tried this. I tried using FD-R9150 along with GRX 48-31 without using chainring spacers and it didn't work. Shifting was sluggish. Figuring that not only the crank's chainline is different, the FD-RX815 most likely has different cage dimensions designed to handle a 17T gap between chainrings. So I ended up buying a FD-RX815 and shifting is now perfect. If you're planning on putting the GRX crank on the gravel bike, the GRX crank might have a different chainline from the FSA crank. It's best to make sure you have a GRX FD on the gravel bike as the GRX FD is designed specifically for the GRX crank. If you do have a GRX FD, then just get the GRX 600 crank and also move the FD to the Domane for the climbing ride. Besides the issues mentioned above, the GRX crank will work nicely with a road group. You might have to shorten the chain and make sure that there's no slack in the chain when in the small-small gear combination.

[alcatraz]

I find the new chainline confusing. Shimano didn't move the cassette outboard.

So how is it better than a road setup? (apart from providing big tire clearance).

To the OP I suggest to look into running a 36t cassette instead of swapping the crank. A friend even runs an 11-40t cassette with his ultegra r8000 gs mech. But that is a bit extreme. Shifting suffers if you go crazy. Avoid using "road links".

But.... if the choice stands between poor shifting or grinding up a mountain, poor shifting always wins. (non racing situation)

Sram makes an 11-36t cassette. Shimano makes an 11-40t.

[pdlpsher1]

The main benefits of the GRX crankset over a road crankset are lower gearing and a big 17T gap in the case of the 48/31 chainrings. The chainline is the distance from the center of BB to the middle of the two chainrings. Rumor has it that the upcoming Shimano Dura Ace has a +1mm chainline to accommodate bigger tires.

It appears that the OP only wants lower gearing for one ride. Since he was already planning on getting a GRX crankset for his gravel bike his solution would be the most economical solution. His gravel bike probably already has a 11-34 cassette. He could move it over to the Domane for the single ride. In conjunction with the GRX crankset, the 11-34 cassette would give him a low gear of 30-34.

[EBH]

An option for lighter gearing us to use a 11-36 sram cassette, which, incidently I do, together with my 6800 46/34 crank and r8000 rd. Aparently this rd, would even handle an 11-40 cassette. I know the r8000 rd is specced for 11-34 cassette.

[EBH]

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[EBH]

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[sennder]

Thanks for the inputs! The chainline was what I was worried about. My gravel bike is running Sram red22 (Specialized Sequoia which the previous owner upgraded to Sram red). I'm assuming I would have the same chainline issues there with the GRX crankset. The GRX crankset was the most appealing because I thought I could I use it on my road bike for the ride, and then move over to the gravel bike (I already have a spare threaded hollowtech BB).

I do have an 11-36 cassette on the gravel bike. I could just stick with the current 50-34 crankset and use the cassette for a 34/36 ratio, which would be very comparable to the 30/32 that I was planning.

I don't think I will buy the GRX FD just for this ride. Will look into the chainring bolt spacers.

Thanks!

EDIT: Checked the front derailleur mount. I don't think I would have been able to get the FD low enough for the 46-30 crank anyway.

[sennder]

I installed the Sram 11-36 cassette on the bike, replacing the Ultegra 11-32 cassette. The R8000 GS RD worked without any adjustment. Even shifted into big-big. I've been following calnago's chain length guide (may he rest in peace), so I had enough slack to not snap anything. Minor b-screw and all good to go.

[ooo]

11-36t is nice, 2x or 1x

[sennder]

The ride went fantastically well. No issues shifting at all. I'm glad I stuck with the 11-36 instead of trying to get a subcompact crankset because I was spinning out on 50/11 on the donwhill.

I'll stick with the ultegra 11-32 cassette for daily riding but it's good to have the 11-36 option for climbs.