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I have a standard GRX 400 set up on my gravel bike & I'd just like to drop the lower end of the gear range slightly.
The chainset is 46/30 but TA do GRX specific rings and a 28T inner option (which is specced to run with a 44T outer). Would 46/28 be likely to cause major issues?
It would push the front mech. out of its max. difference capacity by 1 tooth, but there's room to drop the mech. slightly. It would also put the rear mech. (41T) out by 2 teeth so I'm assuming that there would be slack in the small ring/small cog combination. However, my chain is currently cut according to the GRX method of counting on 4 rivets. I cut a previous chain using the old MTB 2 rivet approach & it was fine, even in big/big so I main be able to gain back a bit.
Is it just a "try it and see?" set up & would a 2 tooth drop even be worth bothering with?
It *should* work. The only front mech i've had lately that won't support "weird"/slightly out of spec combos was an XT front which is limited to a 10 tooth difference. I've got 12 teeth *and* oval rings, and it catches, just, and only when i unload the suspension in certain gears.
Rear mech will be fine.
You probably won't even get slack in small/small with such a small amount out of spec.
First thing I'd do is pop it up on a stand drop it into the inner and just see how clear of the Front mech cage the chain sits with the rear mech at either end of the cassette. Â
When you do the sums there's basically a -4mm difference radially between a 30 and a 28t chainring.Â
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What cassette are you running? Could you fit one with a slightly larger range instead of switching chainrings?
When you do the sums there's basically a -4mm difference radially between a 30 and a 28t chainring
I never was any good at sums, but that's something I hadn't thought about. It might be tight and I did notice that in small/small the chain is pretty close to the chainstay (I am aware that you shouldn't really be in the extreme gears).
I had thought about the cassette option and I think I could run an 11-38 without lengthening the chain or breaking anything if I accidently shift into big/big, but GRX 400 is 10 speed & when I looked around 11-38 10 speed cassettes didn't seem particularly plentiful although I could have a look when the cassette needs replacing.
-- Edit --
Hmm, Microshift do one.
11-40 will be more common (and a very slightly lower ratio than the other options). Pretty sure people have done 11-40 and ever 11-42 with a GRX 2x setup.Â
My bike runs 26 38 at the front with a standard 10 speed Tiagra derailleur. It works just fine. The back is 11-36 with a grx 400 derailleur, again no problems. My chain is long enough to run fully crossed.Â