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Old 12-06-2019, 05:30 PM
sjbraun sjbraun is offline
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GRX chainline

I’m looking for more gears for my BMC monstercross. If I get a GRX 10 speed crankset (46-30,) will I be able to use my current 10 speed XT (M785) front derailleur? If I remember correctly, GRX uses a +2.5 chainline. Can I mix the two or do I need to buy a GRX front derailleur?

Thanks
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  #2  
Old 12-06-2019, 05:43 PM
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jtbadge jtbadge is online now
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There are a few options for subcompact gearing and a chainline suitable for a 130mm rear end. I've had great results with the Praxis Zayante 48/32 on my rim brake crosser.

Will the GRX work.. probably.
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Old 12-06-2019, 06:58 PM
PacNW2Ford PacNW2Ford is offline
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What crankset are you using now? Single or double? I think the GRX has a 46mm chainline (43.5+2.5). Your M785 FD is designed for 50mm MTB double chainline. It may not swing in far enough with the GRX crank.
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Old 12-06-2019, 07:04 PM
ultraman6970 ultraman6970 is offline
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48.8 chain line in the FD from what I can read... the crankset in question is 46.9 apparently......
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Old 12-06-2019, 07:22 PM
PacNW2Ford PacNW2Ford is offline
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Yes, after more sleuthing, these look like better numbers. Still could be an issue with inward swing.
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Old 12-06-2019, 07:49 PM
ultraman6970 ultraman6970 is offline
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The FD has to have a larger number IMO because of the play the chain has, it crosses so...
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Old 12-07-2019, 08:46 AM
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oldpotatoe oldpotatoe is offline
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Quote:
Originally Posted by sjbraun View Post
I’m looking for more gears for my BMC monstercross. If I get a GRX 10 speed crankset (46-30,) will I be able to use my current 10 speed XT (M785) front derailleur? If I remember correctly, GRX uses a +2.5 chainline. Can I mix the two or do I need to buy a GRX front derailleur?

Thanks
One thing to look at, will the tail of the fder cage hit the RH chainstay..if it doesn't, think you are good to go...
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