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GRX upgrade question

Old 02-09-21, 05:05 PM
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tdilf
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GRX upgrade question

A friend of mine is running Shimano Tiagra 2X, 10-speed, hydraulic. She wants to upgrade to 11-speed. She already has an 11-speed cassette. So she needs to get 11-speed: rear derailleur, chain and hydro levers.
She was thinking of going with GRX 600 levers - will these be compatible with the Tiagra front derailleur and Tiagra brake calipers?
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Old 02-09-21, 07:56 PM
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The Tiagra calipers are compatible with pretty much any current gen Shimano road lever, GRX included. The Tiagra FD is compatible with any crank that has a "normal" q-factor, i.e. not the GRX cranks that are slightly wider. The Tiagra FD doesn't use the newer cage though (whatever Shimano calls it), so it will be a little harder to pull than a GRX / Ultegra / 105 that does have the newer cage.

I gotta ask though, given how hard GRX parts are to get right now (even at retail prices), how much of an upgrade is this if she already has Tiagra hydraulic levers? I would just do a partial upgrade keeping the Tiagra levers and brakes, and use the 10 speed GRX RD, FD, crank, and an 11-34/36 cassette if needed. That's pretty much the full 10 speed GRX groupset, except the brake levers don't have texturing, and say Tiagra.
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Old 02-09-21, 08:56 PM
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Originally Posted by tdilf
A friend of mine is running Shimano Tiagra 2X, 10-speed, hydraulic. She wants to upgrade to 11-speed. She already has an 11-speed cassette. So she needs to get 11-speed: rear derailleur, chain and hydro levers.
She might not need a new rear derailleur. Ever since Tiagra 4700 launched in 2015, Shimano's 10-speed road components were changed to use the same rear derailleur pull ratio as their 11-speed road components. In this context, "road" includes GRX: one of my friends has a gravel bike that came with an 11-speed 105 groupset, but when a mishap resulted in destruction of the rear derailleur, he replaced it with an RD-RX400 from the 10-speed GRX400 groupset. It works great.

She was thinking of going with GRX 600 levers - will these be compatible with the Tiagra front derailleur
I *think* 4700 front derailleurs are designed to be pull-compatible with the 11-speed derailleurs. But it's annoyingly difficult to search solid information about this.

Alternately, you could just get an 11-speed road right shifter and keep the 4700 rear shifter.

and Tiagra brake calipers?
Yes.
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Old 02-09-21, 10:01 PM
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Originally Posted by HTupolev
She might not need a new rear derailleur. Ever since Tiagra 4700 launched in 2015, Shimano's 10-speed road components were changed to use the same rear derailleur pull ratio as their 11-speed road components. In this context, "road" includes GRX: one of my friends has a gravel bike that came with an 11-speed 105 groupset, but when a mishap resulted in destruction of the rear derailleur, he replaced it with an RD-RX400 from the 10-speed GRX400 groupset. It works great.


I *think* 4700 front derailleurs are designed to be pull-compatible with the 11-speed derailleurs. But it's annoyingly difficult to search solid information about this.

Alternately, you could just get an 11-speed road right shifter and keep the 4700 rear shifter.

Yes.
The Tiagra front der was redesigned and made to match the higher end stuff. Wish I'd known about the q-factor aspect. I do have them working with a Sram XO crankset but in hindsight, since I had to buy a new der anyways I should have bought the grx.

Really for this upgrade all that is needed is the cassette and chain, as others mentioned the rear der and brakes are compatible. Personally I wouldn't bother with the cost for one extra gear if its already a hydraulic setup as well. I'd like to get the hydraulic levers for my wife and if I do I probably won't concern myself with 11sp unless the levers are a bargain.
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Old 02-14-21, 01:44 PM
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This doesn't seem like much of an upgrade unless her current Tiagra stuff is completely worn out.
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Old 02-15-21, 04:02 PM
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Pretty big expense for what you are gaining. Maybe a different bike is in order?
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Old 02-15-21, 04:52 PM
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This is a carbon frame Specialized Diverge - so good platform to upgrade and fits her well. A bunch of small reasons for the upgrade: gaining another gear, getting GRX ergonomics in the levers, gaining a little more of a climbing gear (going from 34t to 36t sprocket on rear cassette), opportunity to have oil slick cassette and chain.
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Old 06-03-21, 01:03 PM
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I'm sort of in this situation now myself. I'm wanting to upgrade a Tiagra 4700 front derailleur (braze-on) for a GRX 400 version. The Tiagra 4700 FD has a long lever arm which just barely clears a 38mm width tire on my Specialized Diverge. I'd like to upgrade both front and rear Tiagra derailleurs to GRX and thus gain a clutch mechanism in back and more tire-clearance up front.

The most obvious FD compatibility issue is that the chain line for GRX is 46mm whereas Tiagra was only 43.5mm. I'm not sure if one can overcome that difference using the Hi/Low adjustment screws. Also the Tiagra FD has a long lever arm that is absent on the GRX FD (for greater tire clearance) so I'm wondering if shift lever feel will suffer. Perhaps no one here has made this change (maybe because it's too problematic).
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Old 06-03-21, 01:09 PM
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Originally Posted by tdilf
A friend of mine is running Shimano Tiagra 2X, 10-speed, hydraulic. She wants to upgrade to 11-speed. She already has an 11-speed cassette. So she needs to get 11-speed: rear derailleur, chain and hydro levers.
She was thinking of going with GRX 600 levers - will these be compatible with the Tiagra front derailleur and Tiagra brake calipers?
Why? Its really expensive and makes diddly difference.
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Old 06-03-21, 02:46 PM
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Originally Posted by Racing Dan
Why? Its really expensive and makes diddly difference.
see above
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Old 06-04-21, 11:20 PM
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I would just get a rd-rx400 and a 10s 11-36 cassette. If need be a fc-rx600 crank and the matching fd-rx400 to get even lower gears. Much cheaper and compatible with the tiagra STI brifters.
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