Topic starter
Is anyone running GRX400 2x10 with an 11-40 cassette?
I'm guessing that the chain would need to be lengthened to the point where you'd get slack in small/small.
Microshift do an 11-38 which I'm sure would work but Sunrace's 11-40 is cheaper,& has an alloy carrier.
Posted : 12/04/2025 11:02 pm
As it's not recommended to go small-small or big-big, you shouldn't have any issues
Posted : 12/04/2025 11:20 pm
My grx 400 seems very happy on 36 11. Although my front rings are only 12
My opinion is that yes you lengthen the chain. Smallest smallest might be compromised but personally i don’t tend to use that. To me it’s essential it’s essential that biggest biggest doesn’t cause damage
My hunch is that 40 at the back will be fine. It’s officially rated to 36 at the back. Previously i was running a Tiagra mech rated to 32 and it was fine on 36
Posted : 13/04/2025 8:10 am
Topic starter
Cheers.
I appreciate that extreme cross-chaining isn't recommended, however I do like the option to use them as bail out gears, just in case, and certainly wouldn't want to break anything if I absent mindedly shifted into big/big.
Posted : 13/04/2025 9:22 am
Is that bailing out from a mech failure?
Posted : 13/04/2025 10:21 am
Couple of friends run 11-40 on 11 speed GRX. Slightly longer chain, and be vigilant about cross chaining, but otherwise, seems to work well.
Posted : 13/04/2025 12:01 pm
Topic starter
I think that the sensible thing would be to go for an 11-38 (Microshift do one) when the cassette needs replacing, as I'm sure that that would work as is. The chain's cut using the GRX approach of counting back 4 rivets but previously I'd cut one using the old count back 2 rivets & it worked fine and big/big didn't break anything, so I think there's some surplus capacity. 40T might be pushing it too far.
Also I could do with better legs & lungs.
Posted : 13/04/2025 1:44 pm
I ran this before and it was fine, just make sure the chain is long enough. I did avoid the big big but made sure it wouldn’t rip anything off if it was used. I didn’t use a goat link or anything else, just adjusted the b limit to account for the bigger gear.
Posted : 13/04/2025 2:11 pm
My grx 400 seems very happy on 36 11. Although my front rings are only 12
My opinion is that yes you lengthen the chain. Smallest smallest might be compromised but personally i don’t tend to use that. To me it’s essential it’s essential that biggest biggest doesn’t cause damage
My hunch is that 40 at the back will be fine. It’s officially rated to 36 at the back. Previously i was running a Tiagra mech rated to 32 and it was fine on 36
Out of interest what make of cassette and chain do you use? I thought Shimano’s 11-36 10-speed cassette was for MTB only?
Posted : 13/04/2025 6:44 pm
Out of interest what make of cassette and chain do you use? I thought Shimano’s 11-36 10-speed cassette was for MTB only?
"Road" and "MTB" 10 speed cassettes have the same spacing and GRX mechs will comfortably stretch to a 36t (and probably beyond), I know Tiagra (4700) will as well.
IIRC RX400 will officially accommodate 11-34t, 2 teeth more is hardly a stretch, 6 teeth is perfectly doable.
If you look at an RX400 rear mech, it's not much different to the first gen dynasis mechs people first started trying to stretch over 11-40/11-42t cassettes (normally 1x), the main difference being cable pull...
Posted : 14/04/2025 12:02 pm
My GRX400 bike came with 30/46 rings and 11-34 cassette, so that's 39T capacity.
Posted : 14/04/2025 4:03 pm
Yes it’s an slx mtb cassette. Same spacing as road. Needs a spacer on my HG freehub which will take 11 speed
Posted : 14/04/2025 5:18 pm
Topic starter
The GRX400 rear mech has a 41T capacity I believe.
My GRX400 groupset has 46/30 rings & an 11-36 cassette (Deore).
I think that 11-38 would work but 11-40 might require a chain length that would cause issues in small/small (not a recommended combination I know).
Posted : 14/04/2025 5:36 pm
