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I want to upgrade my bike to a 1x system using a Shimano GRX-crank upfront.

I however have a flatbar and can thus only fit flatbar shifters.

What is the lesser evil?

  1. 11-Speed XT derailleur with XT shifter and GRX crank
  2. 11-Speed GRX derailleur with XT shifter and GRX crank

Thank you in advance.

EDIT: I forgot to mention that everything including the rear wheel and cassette will be new.

3

I have found that Shimano offers non-series road flatbar shifters such as the 11-spd SL-RS700.

So this one can be used with GRX-derailleurs, as GRX is compatible to all roadbike components Shimano offers.

The original source (in German) is here : https://www.mtb-news.de/forum/t/shimano-grx-schaltwerk-flatbar-schalthebel.908787/

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  • Good answer. I knew that Shimano offers flat bar shifters in Tiara and below but I was not aware of the 11 speed versions. – Argenti Apparatus Jan 26 '20 at 18:53
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    The compatibility chart seems to confirm that the SL_RS700 shifters are directly compatible with GRX front and rear derailleurs. The MTB charts don’t say anything about the shifters, however. productinfo.shimano.com/#/com?cid=C-453&acid=C-455 – Weiwen Ng Jan 26 '20 at 22:33
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I'd go with XT 11 speed shifter and derailleur. Shimano does not publish MTB-Road groupset cross compatibility and I'd assume GRX and XT are not compatible.

I think a bigger issue is whether a GRX crank is compatible with your bike.

GRX cranks are designed to fit road-like gravel bike frames which may have a narrower bottom bracket than MTB frames. If you have a MTB frame you'll need to look at what cranks are compatible. You might want an MTB crank with a larger chainring installed rather than a GRX crank.

Many MTB frames can't take larger chainrings because they would interfere with or have insufficient clearance with the chainstay, so check how large a chainring you can fit.

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  • i searched for cross-compatibility and i think you are right. My frame is an old roadbike frame with a a BSA68 BB so i am certain it will fit, but thanks for the headsup nonetheless – a1o Jan 26 '20 at 17:31
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First: Shimano GRX road/gravel derailleurs and shifters are NOT compatible with the mountain derailleurs (XT, XTR, etc). So an XT shifter will not work with a GRX derailleur.

The GRX and other road bottom brackets are only offered in 68mm and 70mm widths so they will not fit a mountain bike's bottom bracket which is 73mm.

The XT has a 73mm bottom bracket which is standard for mountain bikes and it can be installed with two 2.5mm spacers onto a road/gravel frame that has a 68mm bottom bracket shell. This is how my commuting bike is setup. BUT this pushes the chainrings farther out to the right so I needed a mountain front derailleur to shift onto the big ring.

The GRX front derailleur may not be able to push the chain far enough to the right to work on a mountain bike. Again this would be due to the 73mm bottom bracket.

So to answer your question fully one needs to know the bottom bracket width: 68mm or 73mm?

For the best compatibility and fewest issues I would recommend using parts intended for the specific bike. If the bike has a 68mm BB shell then I'd suggest the GRX. If it's 73mm then I'd suggest XT.

Another factor which may influence your final choice is the gear ratio options for highest and lowest gear. Road/Gravel gearing is significantly higher than mountain bike gear ratios.

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