Ok, 8100 derailleur and shifter, sunrace 903 cassette and X01 chain work really good. Haven't seen Shimano chain in action, but this setup works faster and quieter then old, pure 8000 one. Both with BCD104 AB oval chainring.

 

I'm going to hazard a guess that most of the improvement people are seeing from moving the b-screw adjustment closer than shimano guidelines indicate is because it lessens the effect of the derailleur misalignment. Do yourself a favor and triple check the alignment before you grind your guide jockey wheel into the cassette.

 

Do you mean derailleur hanger / dropout alignment? I've been wondering if I should get the tool / take mine into an LBS to have it checked.Also @kopter28, where did you find this upgrade kit?

 

Its not as much alignment, as it is lower the B screw so that when shifting to smaller cogs, there is enough tension to pull the chain off the larger cog so it will drop. Thats why dropping the B adj is working.

these cassettes just have to be set up perfect, they dont have sram or shimano quality.

Same alignment with a scram eagle gx set up, and it shifted perfect with a large window for error on B adj and the barrel adj. With sunrace the B and barrel has only one spot it really works well in.

One should make sure they hanger is not off, but here the main issue is the cheap cassette

[edit] those with 11s use the sram gx 12s chain, its not a game changer, but worked better then the knc or shimano chain

 

Mine recently stopped downshifting off of the biggest cog so I loosened the b screw a quarter turn and that solved the problem. But, I don't think chain tension defines the problem accurately for three reasons:

A. When the chain is on the biggest cog the chain tension is higher than on any other cog but I only have trouble downshifting from the biggest cog.

B. When the b screw is backed off, I believe it reduces chain tension.

C. The main affect of backing off the b screw is the jockey wheel moves closer to the cassette and there is less chain between the cassette and the wheel. That should directly improve shifting performance. On other drive trains I have had (non 12 speed) the jockey wheel is much closer to the cassette and they work great.

I would like to know exactly why other 12 speed cassettes work so much better than the SunRace. I suspect it has to do with proprietary design but I'm curious for details.

Anyway, I agree that everything has to be set perfectly for the shifting to work right. It is possible that it would work with a wider range of adjustments if the jockey wheel was set even closer but it is not worth the risk.

 

There is a price for going cheap on a very critical component, fine tuning or nothing, unless your lucky

Right, but I can't get a 12s cassette from Shimano that'll fit on my hub... :/ So it's gotta be the Sunrace, and at least now we know how to make it work? ... unless someone has a story of setting it up like this and it still not shifting right?

Also, what do the installation / dealer instructions say?

 

Right, but I can't get a 12s cassette from Shimano that'll fit on my hub... :/ So it's gotta be the Sunrace, and at least now we know how to make it work? ... unless someone has a story of setting it up like this and it still not shifting right?

Also, what do the installation / dealer instructions say?

Another option that I heard works better is the SRAM NX Eagle Pg-1230 Cassette 11-50, 12 speed. It costs about $90 but it is all steel and weighs 100 grams more than the Sunrace.

 

I have a feeling the extra ramps Shimano added to the larger cogs of the 12S (and M5100 11s) account for the larger B-Gap. This appears to let the chain drop even though the derailleur is a bit further; something the Sunrace does not have or is not as defined. So the Sunrace must be set up closer / tighter. I have all 3, M5100 11S, SLX&XT 12S and SLX running with the MZ903. All can be made to shift excellent but the Sunrace has a few more intricacies as most have documented in this thread. I've been using Sunrace's newer lines since the MX3 10-speed and have gotten good life they are a decent value. With all of that said, I'd still take an 11-speed XT M8000 Shifter, M5100 (or any Shimano 12S) RDR, and the M5100 cassette over the Sunrace if Microspline was not an option.

 

Is there anyone running l/interchanging MZ903 and microspline wheel on same bike? Are adjustments needed (outside of b screw) or can wheels we straight swapped? Considering a training wheel and a race wheel (and spare for tech zone) on same bike.

 

I have a brand new wheel fitted with XT cassette, but I am still waiting for the Sunrace cassette to die, hopefully sometime next year.
I don't think you'll have to do anything else but the B tension.
I am more than pleased with the Sunrace cassette. Since I got it working right I never had any problems, nor have I made new adjustments. 8 months now.

 

Hey all. Sorry to revive an old thread but I've been digging through it for about an hour pondering my situation.

My current setup is kind of odd but I like it a lot for what I do:

Norco Search XR frame

Sunrace 11-51 cassette
Shimano m8100 XT derailleur
Ali express crap 104BCD chain ring - upgrade to Raceface or Wolf Tooth?
SRAM GXP cranks

Thanks for all the info. Since this thread was active, has anyone upgraded to microspline wheels/hub? What did you get and how did it work out? I'm considering a DB Swiss E1900 to go with an XT cassette, but I'm unsure how to tell if it will fit my frame.

Is there a particular front chainring that works best with this setup or does any old 104 BCD chainring work? What are you all using?

 

To get the benefit of the improved shifting you need the Shimano 12 speed cassette and chain. Most of the Ali express n-w chainrings will work with the 12 sp Shimano chain. Paradoxically it's the more expensive ones that were super optimized for 11 speed that don't.

As far as what rear hub fits, just measure the current one. Current specs on that bike are 12x142.

For the cassette just buy whatever X100 level fits your budget. They all work equally well.

 

Recently I have had 2 different bike on which the largest cog have trouble releasing the chain to smaller cogs. One is an XT 12sp shifter, cassette and derailleur, the other bike is deore shifter, cassette and derailleur. Same problem on both. I have done about 1k - 1.5k km on the XT cassette (swapped chain twice) and have put on fresh smaller steel cogs. On the other bike I have done around 1k km, swapped chain once and not swapped smaller cogs. Same problem though, largest cog does not shift to smaller cogs (even after multiple shifts) unless I release the clutch. After that it shift perfectly. The b-tension is where shimano recommends. Serviced the clutch, same problem. Swapped chain same problem. Tried adjusting clutch with less tension, but only by releasing it enough so it practically did nothing would the shifting improve.
The only thing that made it work was to release the b screw a bit so less tension on the chain than recommended.
This also worked on the other bike, after I figured out what to do.

It's strange because it has always shifted perfectly, until suddenly it didn't. I can't say for sure on the deore bike, but on the XT bike I am fairly sure I haven't hit anything to misalign the dropout.

In both cases it happened after lots of muddy rides and dirty derailleurs. I have deep cleaned both derailleurs after though, and made sure the in/out action with the spring functions smooth and properly.

I have no idea really, I'm just happy it works now but puzzled why the solution was to move the b screw.

Use my test and trials to what you want. Maybe it helps someone, that's my hope at least.