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Hi everyone,
So I'm building my first full sus frame up with a new Shimano XT (M8100) 1 x 12 drive train.
Built a few hardtails up in the past with 1 x 11 but really struggling with the 1 x 12 and getting the right chain length.
I've used page 13 of this document as a guide;
But the chain is terribly baggy when on the highest gear. I'm totally lost and the more I search the more confused I get.
Any advice on getting the correct chain length would be greatly appreciated as following the Shimano guide isn't getting anywhere close to the results I need. Thank you.
Show us a picture of how the mech looks in the biggest sprocket
Thank you, shots of highest and lowest.
Is that a long cage mech? Also, is your chain sat on your chainstay in the highest gear??
Have you sorted b tension
Yes, it's a long cage, I bought the 1x12 upgrade kit here;
https://r2-bike.com/SHIMANO-Deore-XT-Upgrade-Kit-M8100-1x12-speed-Cassette-10-51-Teeth
Yes, the chain is sat on the chainstay in the highest gear 🙁
I've had this before, followed instructions to set length and it was too baggy, just took two links out then it was spot on.
Have you sorted b tension
That was going to be my next question
If that's ok, them you can probably/definitely get away with taking a link out.
Not sure that's going to sort your chainstay issue though, unless it's just the sag that's making it sit on there
FlareMAX? Ask Cotic. Then you've eliminated length as a potential cause and can focus on adjustments.
had similar when i went AXS and also swapped to a 52 tooth cassette. set length as per sram instructions and was very slack, ended up taking 2 links out to sort it. removed shock to check it allowed full travel in the 52 tooth and its been fine for the last 10 months.
Isn’t the chainstay problem going to even worse once you’re sat on it?
For comparison my gen4 flaremax with slx12 speed mech, xtr cranks. Looking again at your 4th image, it doesn't appear too baggy as there is tension keeping the mech forward.
EDIT: Forget that, I thought they were talking about chain clearance not chainring clearance.
I've had real trouble with 12S and long cage mechs on suspension bikes. It's a very fine line between baggy as hell in bottom gear and stupidly tight in top (which reminds me that I need to look at K's as it seems too short now)
yep next as a few have already mentioned above is to set the B adjust using the marks on the back of the cage, you will probably find the mech needs to move quite a bit further out and this will take up a little bit more slack.
Page 23 on in that guide:
Thanks everyone for there support and ideas on this.
I decided to take the derailleur off and start again. This quickly flagged my error and stupidity.
Simply, I had the stopper that is part of the derailleur for the B Screw not sitting in place. So the B screw was hitting the frame stopper and not the derailleur stopper.
All good now and a step closer to riding.
Thanks again for your help.
