Shimano GRX812 rear...
 

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[Closed] Shimano GRX812 rear derailleur - alternatives

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New Gravel bike one week old - 11-42 cassette, wrecked the rear derailleur. Being told 27th August for part. Does anyone know of any other options to fit that will work with that range? This is depressing 🙁


 
Posted : 01/03/2021 1:11 pm
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Ultegra would work i think, not sure which model


 
Posted : 01/03/2021 1:22 pm
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Unless I'm mistaken the 812 mech is designed to work with a standard 11spd MTB cassette so I believe that any 11spd MTB mech shoudl also work.!

#EDIT : So on looking into it a bit more it seems that the 812 GRX is a bit of a unicorn in that it's designed to work with road shifters and an MTB cassette. It looks like they achieved this by altering the pull ratio of the mech to get it to work..  There seems to be limited information about it so in your shoes i'd be wary of buying an MTB mech.  Can you beg/borrow one and try it.?

FYI though, while looking into it, apparently you can use the Wolftooth Goatlink for 11spd MTB mechs to get a GRX mech to shift on an 11-50 cassette if you wanted more range.


 
Posted : 01/03/2021 1:26 pm
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Note to self: Don't mangle my 812 mech.

Thanks OP.


 
Posted : 01/03/2021 2:03 pm
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How did you manage to damage it?


 
Posted : 01/03/2021 2:04 pm
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Ultegra RX.

Which was basically the prototype for GRX. Works fine on a 42t MTB cassette in my experience.


 
Posted : 01/03/2021 2:05 pm
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Ultegra RX.

Which was basically the prototype for GRX. Works fine on a 42t MTB cassette in my experience.

So this seems like the obvious answer but Ultegra RX is designed to work with 11spd road shifters and an 11spd road cassette.  Now there isn't a huge difference in spacing between 11spd road and 11spd MTB but there IS a difference and while I would say it's certainly worth trying I don't think you can say with certainty that it will work in all setups.

FYI spacing between gears is 3.74 mm (road) and 3.9 mm (MTB) so it may or may not work for everyone depending on frame/hanger/wheel/mech/cassette interaction.


 
Posted : 01/03/2021 2:29 pm
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I believe you can use a Wolftooth Tanpan with an MTB 11spd rear mech to replace a GRX one.


 
Posted : 01/03/2021 2:32 pm
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A few on this thread using rx800 with 11-40 or 11-42 cassettes

https://singletrackmag.com/forum/topic/shimano-rx800-ultrega-derailleur-will-it-work-with-11-42/


 
Posted : 01/03/2021 2:33 pm
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All kind of irrelevent anyway as the RX800 is as out of stock as everything else.!!! 🙁


 
Posted : 01/03/2021 2:42 pm
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There are a couple available on ebay if you don't mind getting them shipped from the States.

Ebay link


 
Posted : 01/03/2021 3:34 pm
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Note to self: Don’t mangle my 812 mech.

Yeah no kidding. I've been counting myself lucky to actually get my hands on a new bike in the last few months and I can imagine being unable to get spare parts for it would be super irritating.


 
Posted : 01/03/2021 3:56 pm
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PM'd you.


 
Posted : 01/03/2021 6:15 pm
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I emailed Maddison earlier this week regarding availability of GRX 810 1x rear mechs, just had a reply back saying ETA is currently September!


 
Posted : 12/03/2021 4:21 pm
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just had a reply back saying ETA is currently September!

You'll be lucky. They're saying that now, but they'll slip again before then.


 
Posted : 12/03/2021 4:30 pm
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Have used a Ultegra RX with a 11 speed 11-40 cassette with no issues.
This was on a 1x set up though with a 42 tooth chainring.
Can't see a 42 tooth on the cassette would give it much trouble but if a problem surely a goatlink would sort it out.
Thanks,
Max.


 
Posted : 12/03/2021 4:30 pm
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Does anyone know the reason for such a long delay with these ?


 
Posted : 12/03/2021 4:40 pm
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There are deliveries quite frequently - it’s just that they’re pre-sold.
I ordered one at the end of December - due date is early next month. Demand isn’t slowing, so later drops are selling out fast.
Due date on a fresh order is September as I type.


 
Posted : 12/03/2021 8:16 pm

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