Check This, Before You Snap The Chain On New Shimano 1x12 SLX, XT Or XTR Drivetrain... 

I am running 1x 12 10-51T but my derailleur (8100) was broken and Shimano replaced the part for an 8120, I was able to install it but I notice the shifting is not that quick and soft. I can see the 45T line instead of the 51T. Should I request the 8100 instead?

Will the xt m8000 have this same guide too?

Good vid, except for that error. I don't have the new kit, but was researching it the other day and read the Shimano literature about the B settings, so I picked your mistake and then came looking for a correction. It's interesting how the 2x mech has the extended measured distance for 1x set-up. This shows that the line is basically a minimum mark (to an extent.) The extra B gap for the 1x must be for cross-chained chainline angling through the pulleys? So if you want to crosschain with 2x (like say use all but the 45 when in the 36 ring) I wonder if it's better to increase that B gap a bit from the line, more like the 1x measurement. I can't see how that would have a bad effect on shifting when in the granny, especially when NOT cross-chaining the granny. When I get the cash I'm considering building a 2x12 and ditching the pointless 26/36 chainset for a custom crankset combo running a 14t step (with an appropriate FD from a different group) for 22 or 24 granny, with a 36 or 38, paired with the 10-45 on a 700/29 wheel to get awesome range for steep climbs and bikepacking climbs, while keeping a couple of high gears for winding it out along roads. Gravel riding could go 28/42. I know the 11-42 11 speed option is similar, but getting that ultra low climbing gear, combined with the great 12 spd gear steps and top end, is something I'd love to try, especially to show how it might actually work. So your in-depth look at such mechanics as this is very useful. Thanks.

On cues u have marker for 51t and 48t❤

Of course they don't set it up if you have to do anything when you get a bike that's set it up.

Shimano did IT better. No need for a Tool👍

thank you!!!

True. I always use this technique when shifting the gears.

there is a line with my sgs M5100, its black.

Great. If the RD was to high, then it will feel less stiff on the lowest gears, if it was to low, it will shift quicker.

Try 3x10 (If you can get the first 10 speed MTB derailleurs and shifters before they beefed up the return spring in the derailleur and made shifting a heavy, clunky misery (Like SRAM)). The shifting on 10 speed is noticeably quicker and cleaner than 9 speed. 12 speed claims to be a similar jump forward compared to 10 and 11 speed. Hope they've sorted out the shamefully heavy shifting.

Me too. In fact I went bike packing on a 1990 stump jumper and the old deore DX gears shift as well as any bike I've ever ridden.

@@peglor thx bro but i ride my bike only in the city don't need quickly gears change 😁😁

Your chain may be too short, too much pull on the deraileur.