Straight swap possible between Ultegra crank with GRX?

I'm looking to swap an Ultegra crank with a GRX 2x on my 2019 Giant Revolt. Someone said I need to replace the front derailleur too. Is this true?

That's the way I read it, they have moved the chain line out by a couple of mm to increase tire clearance.

BS

OltreForza wrote:I'm looking to swap an Ultegra crank with a GRX 2x on my 2019 Giant Revolt. Someone said I need to replace the front derailleur too. Is this true?

Well the q-factor of the cranks differs by 5mm, 2.5mm each side. It's true that chainline is different by 2.5, and also derailleur of GRX takes this into account. GRX derailleurs are made for 46-50 big ring, Ultegra for 50 big ring. 48 big ring could still work okay with Ultegra derailleur, 46 big ring not so much. So depends which 2x GRX chainset you opt for. Finally there are shims to move a derailleur outward, so this could help with the 2.5mm. I think it's a good option if you were planning to go for a 48 big ring. For 46 big ring I would replace the front derailleur.

It's kind of hard to predict, given that the GRX components are not yet on the market.

You may need BB spacers too, but dont quote me on that.

Also the current FD might work, just not quite as well.  2.5mm isnt much.  Ultegra cranks come in 46/36, so the big ring size isnt a limiting factor