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i was thinking of upgrading my GRX FC-RX600 crank which has 46 tooth only and since i ride mostly flat sections, i want more teeth on my big chainring since i am running out of gears. thus the question: can i use chainrings that fit ultegra crancs such as https://alugear.com/chainrings-2x/332-17615-round-2-speed-outer-for-110-bcd-4b-shimano-asymmetric-2x11.html#/11-color-black/39-size-50t? thanks in advance

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    Do you really run out of gears when not sprinting in a race finish? You should be able to go 50 km/h with 46/11 at cadence 90. Apr 2 at 11:13

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It's the kind of change that comes often with additional changes.

Changing only the big ring would not be enough, as front derailleurs are designed around the chainrings dimensions: you'll need to change the small ring as well. And even if you could change the rings, the front derailleur will not fit. Given GRX and road groups have different chainlines, that would imply you can't simply use a "road" derailleur on a GRX crank even if it could fit the rings.So what could potentially work is a road crankset with a road front derailleur, but your frame needs to be able to fit that kind set up (clearance around the crankset, and the FD is brazed on, that the mount has enough freedom of movement to allow that).

If you are willing to give up the small chainring and the front derailleur (assuming that you currently have a 2x - Shimano doesn't have a 46T 1x), an alternative would be to convert the bike to 1x (GRX cranks can do both), some 3rd party manufacturers are selling larger 1x rings for GRX cranks (Wolftooth goes up to 52T - again, your frame needs to be able to clear that size of chainring). To compensate for the loss of the small ring, you may need to change the cassette and the rear derailleur as well.

But as suggested in a comment, if you are interested in performance, working on your cadence is the best approach: it doesn't cost a thing, and higher cadences are less tiring if you like to ride for longer durations.

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  • Thanks, but then do you by any chance know about a vendor that sells chainrings for grx? I mean i could buy the 48 tooth chainring from the fc-rx800 series which should fit I think but that is the maximum of teeth I could get this way
    – macman
    Apr 2 at 13:18
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If you Google, you should be able to confirm that GRX cranks use a 110mm BCD for the outer ring, and an 80mm BCD for the inner ring. Therefore, you can’t simply put Ultegra chainrings on a GRX crank. Additionally, the Alugear chainring has a cutout for the asymmetric spider arm on the 9100/8000/7000 series Shimano cranks, and the GRX cranks don’t have that asymmetric arm.

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