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I have a GRX400 group set on my gravel bike and was toying with the idea of trying to extend the low end of the gears whilst whilst leaving the 46 tooth ring in place.
I can get a smaller inner chain ring &/or a cassette with larger cogs, but in the default set up the rear mech. is at full capacity (41T).
I'm aware that the GRX400 cable pull matches 11 speed road but there is/was a thread on here suggesting that a 9 speed MTB mech. would work as a 10 speed GRX mech. Does anyone know if this extends to 10 speed MTB or is that different. Specifically I was looking at a T6000 Deore mech. that has 47T capacity.
Shimano 9 and 10 speed MTB mechs definitely have different pull ratios. I wouldn't have thought either would work in a GRX 10 speed setup.
You could use a 9 speed MTB mech in an old Shimano road 10 speed setup, but as you've noted, GRX 10 speed uses the same pull ratio as 11 speed.
Thanks. It sounds like the T6000 is out then. I don't suppose, by some miracle, that the new CUES rear mechs would have the same cable pull as GRX? I doubt it.
For reference, the thread I was referring to that talked about using a 9 speed mech with GRX is this one:-
https://singletrackworld.com/forum/bike-forum/grx-10sp-pull-ratio/
CUES is Linkglide, I think, which is not the same pull as any Hyperglide. Cues only works with Cues.
A quick Google suggests that CUES (which replaces the old T6000 & T8000 trekking kit) is 1:1, so I guess not.
Sorry, impossible to edit posts as they vanish for hours!
Google's AI Overview is telling me that the GRX cable pull ratio is also 1:1, although of course, this is AI so I've no idea if it's correct. If this is correct I could use a RD-U6020-10 which has a 44T capacity & 39T Low Sprocket Max? I suspect that mixing Linkglide & Hypeglide components is probably a non-starter.
Google AI
The Shimano GRX cable pull ratio is "1:1", meaning for every millimeter of cable pulled by the shifter, the derailleur moves the same amount, making it compatible with most standard road bike shifters and derailleurs.
I can get a smaller inner chain ring &/or a cassette with larger cogs, but in the default set up the rear mech. is at full capacity (41T).
I din't know if it works with a GRX400 mech, but there's a hack out there where you swap out the mech cage from the GRX derailleur with one from a long-cage XT one. Google should give you the basics, sorry I can't remember the full grizzly details offhand, but I went as far as buying the mech cage from SJS Cycles with a view to doing just this.
Also bear in mind that Shimano's official capacity figures are quite conservative, so you probably have a little more lee-way than you think.
Google's AI Overview is telling me that the GRX cable pull ratio is also 1:1, although of course, this is AI so I've no idea if it's correct.
Pretty sure it's AI lies, or there'd be loads of people running GRX/SRAM hacks.
Also: "making it compatible with most standard road bike shifters and derailleurs" - I don't really think there's such a thing as a "standard" road bike shifter/derailleur.
Thanks everyone.
The best option would probably be to stick with the 11-38 cassette or 28T inner ring option. Either takes the rear mech. a couple of teeth over capacity (and the smaller chainring pushes the ring difference out for the front too) but I suspect that it's workable.
Also, my chain is cut using the GRX advice of counting back 4 rivets from the meeting chain ends. Previously I mistakenly cut on using the old MTB 2 rivet approach and everything worked without issue and I could still shift/run in the big cog/big ring without damaging anything. I could go back to the 2 rivet length & remove a bit of slack (gain back 2 teeth?).
All current road and gravel 1O and 11 speed are the same pull ratio. So you can just use a larger capacity grx 600 series rear mech. Or you can use an extender
This article is a bit dated but still useful
https://road.cc/content/feature/how-get-ultra-low-gearing-gravel-bike-adventures-246424
FYI I'm using tiagra 10 speed shifters with a range of mechs including 105 and grx 400
I have a 24 38 chainset from spa cycles and a 36 11 block
All flavours of GRX use the same pull as Road from 4700 on (1.4:1 IIRC)
MTB 10 speed onwards (dynasis) used 1.16:1 (again IIRC), MTB 7/8/9 speed and road 7/8/9/10 speed all used "2:1" (Which was actually more like 1.7:1)...
Dynasis mechs will not work with GRX shifters... Unless you try a tanpan...
Having said all of that, I bet you could get a lower sprocket to work there is an 11-46t 10 speed deore cassette that's pretty cheap, with a road link it might be persuaded to work(?) Shimano are know for being quite conservative on their listed max sprocket sizes.