guidodg

Will a Shimano GRX800 wide derailleur work with an 11 speed 11-51 cassette?

My friend currently has an 11-42 cassette on his Cannondale Topstone with a 40T but he needs easier gearing...so can I fit a larger cassette using his existing derailleur?

Obviously the chain will be too short.

Any advice on which 11 speed cassette?

Thanks in advance!

delbiker1 

https://www.garbaruk.com/rear-derail...-11-speed.html

That is a link to a long derailleur cage for the GRX. Though the stated max for GRX is 42 tooth, you can likely stretch that out a bit. The Garabuk cage states max of 51 tooth.

veganbikes

It won't work with something that large. GRX is 42 max I believe and while you could maybe eek out a few more teeth I would just pick a different front ring and call it a day.

The Garabuk cage looks neat but a bit more faff than a new front ring. Though they did make one for Di2 so I am kind of thinking damn I could build up the bike I want.

Mtracer

I don't think there's anyway the stock derailleur would work. It has a stated capacity of 31T (what you get now with a 11-42 cassette). While Shimano is known to be conservative, and you could work with a somewhat larger cassette, I don't think you could push it to an 11-51. Maybe that Garbaruk cage delbiker1 linked would work. But aside from the cage, you need pulley wheels, though maybe you could use the wheels of the existing derailleur.

I think the reality is your friend should have gotten the the 2x instead of the 1x setup. While a smaller ring upfront would give him a lower end, even a 40-11 combination isn't a lot of top end as it is. If you reduced that to be the equivalent of changing the cassette from a 42 to a 51, you would need a 33T ring and top end speed would be about 25 MPH at a cadence of 100 RPM. Plenty high on the flat for a mere mortal, but they would spin out on most any fast descent.

Of course, this all depends on how they are using the bike. If they are really doing mostly off-road and more trails than fast gravel or paved roads, then maybe they don't need much top end and a smaller chain ring is the simple solution.

guidodg

Thank you all for the replies.... which derailleur will work with a GRX800 gravel lever and a 11-51 cassette?

Mtracer

I don't think there is any derailleur that will just work. The GRX uses a road shifter cable pull and you're looking for a MTB range derailleur. For whatever reason, the Shimano road and MTB system are not comparable, at least for 11 speed. Meaning, the amount of cable pull to shift to the next gear is different between road and MTB systems.

But what you could do is use an MTB derailleur like the Shimano Deore RD-M5100-SGS which is rated for an 11-51 cassette. But again, this uses an MTB pull. So, you could use is a Wolftooth TanPan device. This is a little pulley thing that will convert the pull of a road shifter to the pull of an MTB derailleur. I've used one before and it works quite well.

https://www.wolftoothcomponents.com/products/tanpan

I think this could be a better solution than trying to extend the range of the exiting derailleur with a longer cage. You'd be using a derailleur designed for exactly the cassette you want to use.

Also, if you decide to go this route, please double check my suggestions to make sure it is what you need.

guidodg

ok, cheapest and easiest is a 38T with an 11-46....

living in South Africa the aftermarket components are hard to get unfortunately...thanks so much for all your kind help!!

The Chemist

Just bought a GRX800 (812, medium cage) derailleur to use on my gravel/commuter bike. Will install it later this week and hopefully it will work with the 42t chainring and 11-46 cassette I currently use. According to information I found online before purchasing, it should work, but I'll update here if it does or doesn't.

The Chemist

I just installed my GRX 812 Derailleur on my 42t / 11-46t gravel / commuter bike a couple of days ago. The derailleur DOES work with the 11-46 cassette, but I doubt you'd be able to go any bigger than than that (and almost certainly not 51t), as the shifting is not as precise as it would be with a smaller cassette and you don't have much more adjustment on the B-adjustment screw at this point since since you need to push in the B-adjustment screw close to all the way to get it clear the 46t large cog.

50PlusCycling

I recently installed a GRX 820 12 speed driveline on a bike I was building, it is a 1x11 with a 10x51 cassette. The derailleur would likely work on an 11 speed bike, though the jockey pulleys would probably have to be changed because of the different roller size on the 12 speed chain.

csport

This S-Ride claims to work with a 50t max cog.