[Harold]

Unfortunately the chain will drop down 4 cogs on a backpedal from the 51T cog in about 1.5 to 2 full revolutions of the crank arm.

That's actually not bad. In real-life usage, backpedaling that much is pretty rare. When I backpedal to ratchet, or to clock the pedals, 1/4-1/2 a rotation is fairly typical. 3/4 of a rotation is uncommon, and a full rotation is rare enough. I certainly test it to failure in the workstand, and I'm happy so long as I can fairly reliably get real-world use out of it without problems.

 

[Evintos]

That's actually not bad. In real-life usage, backpedaling that much is pretty rare. When I backpedal to ratchet, or to clock the pedals, 1/4-1/2 a rotation is fairly typical. 3/4 of a rotation is uncommon, and a full rotation is rare enough. I certainly test it to failure in the workstand, and I'm happy so long as I can fairly reliably get real-world use out of it without problems.

I'm with you there :thumbsup:.

I know some people gotta have that absolute 0 chain drop though. For them, this cassette is probably not one they'll be happy with despite the positives of price (listed price $74.90 on eBay for the black), HG hub, and Shimano 12sp drivetrain compatibility.

 

[higuygonen]

Hi, why you set the b tension lower than the marks, how it function when it was set as manual?

 

[Evintos]

And it works quite well.
I continue to test, the only thing I notice is that sometimes at 'up shifting' it took some time to shift (only at the middle cogs).
I think I need to adjust it again after break in.

https://forums.mtbr.com/drivetrain-shifters-derailleurs-cranks/sunrace-csmz903-11-51t-1116487.html

Hi, why you set the b tension lower than the marks, how it function when it was set as manual?

When it was set according to the manual, I experienced the same thing you did. Middle cog shift hesitation/delay/lag. If I tuned the cable tension for faster upshift (using barrel adjuster), the downshift in those cogs would then experience the shift hesitation. Shift speed with the B tension set according to the manual was approximately 1 to 1 1/4 revolution of the crank arm in the middle cogs to complete a shift. The exception was the 33T to 28T shift, which required upwards to 3 full revolutions for completion.

The shift speed of the largest and smallest cogs were unaffected with shift speeds being 1 revolution for the larger cogs and 1/2 revolution for the smaller ones.
[HR][/HR]
With the B tension lower than the marks, I was able to achieve fastest shift times. Shift completion speed in the middle cogs with this setting is 1/2 to slightly under 3/4 revolution (if I had to approximate it, largest middle cog required 0.7 to 0.72 revolution of the crank).

The smoothness of each shift with the different B tension settings was not affected. Only the speed in which the shift completed.

 

[higuygonen]

Thank for the accurate info, i will given it a try.

 

[PuddleDuck]

Hi Evintos,

I'm super glad that this worked out for you :thumbsup:

Also, thanks for posting such detailed info on the way you've set up the new cassette and how you've optimised shifting.

 

[PuddleDuck]

Side notes:
Casual observation, I believe the spacing between cogs CSMZ903 is narrower than that of the of the CSMZ90. I haven't confirmed with feeler gauges though so perhaps my eyes deceive me..

This info from another forum confirms your observation; you eyes are well calibrated :yikes:

https://weightweenies.starbike.com/forum/viewtopic.php?t=152690

Cog Spacing
- 12s Shimano 3.55 mm
- 12s SRAM 3.65 mm

Cassette Width
- 12s Shimano 39.05 mm
- 12s SRAM 40.15 mm

 

[Harold]

I'm with you there :thumbsup:.

I know some people gotta have that absolute 0 chain drop though. For them, this cassette is probably not one they'll be happy with despite the positives of price (listed price $74.90 on eBay for the black), HG hub, and Shimano 12sp drivetrain compatibility.

If you want absolutely zero chain drop, you probably shouldn't go past 10spd, then.

 

[Ixaxaar]

Great thread and first post! It helped me sort out that problem. I am even lower than the mark and it shifts like butter - super fast and fine, and even no issues with back pedal - I have to do 7-8 whole turns before the chain drops, if it drops.
One slight problem stays however. When I am on the 51-st there is a slight rub of the derailleur in the spokes, but just on a single place, not the whole thing.
If I make it not to rub, then slight shifting problems appear - hesitation from the 9-th to the 8th cog or from the 10-th to the 9-th, have to double check.
Let me know if you have this issue.
I am with an oldschool 135 rear end if that matters. With a 34 front, I don't have a use for the 51-st cog, but I might use it for a few minutes in very steep climbs.

Merry christmass boys and girls, have a great one comming!!!

 

[PuddleDuck]

Great thread and first post! It helped me sort out that problem. I am even lower than the mark and it shifts like butter - super fast and fine, and even no issues with back pedal - I have to do 7-8 whole turns before the chain drops, if it drops.
One slight problem stays however. When I am on the 51-st there is a slight rub of the derailleur in the spokes, but just on a single place, not the whole thing.
If I make it not to rub, then slight shifting problems appear - hesitation from the 9-th to the 8th cog or from the 10-th to the 9-th, have to double check.
Let me know if you have this issue.
I am with an oldschool 135 rear end if that matters. With a 34 front, I don't have a use for the 51-st cog, but I might use it for a few minutes in very steep climbs.

Merry christmass boys and girls, have a great one comming!!!

Merry Christmas to you Ixaxaar

It's annoying that you have that rub in the 51. Solutions that come to mind are:

1. re-check the derailleur hanger alignment, in case it's causing the problem.
2. install a e.g. 1mm spacer behind the cassette to space it out (ensuring that the chain and/or smallest 11t cog doesn't hit the chainstay/dropout)
3. get "creative" with the 1 spoke/spoke pair that the derailleur hits...creative in terms of bending that bad boy of a spoke out out the way...and doing any re-truing of the wheel that's required...it's a pure "brute force and ignorance" strategy...but if that's what it takes to be safe, then you have to do what you have to do!!

Could you post a few pics of the rub?

Also, what chainline are you using. What ring on what crank?

 

[Ixaxaar]

Hey, thanx for the reply!
The derailleur hanger is 100% alright. What kind of spacer are you talking about?
Actually, the rub is only present when I'm on the trail and when I'm on the bike. When the bike is on the workstand - there is no rud I can hear or see. I am not a heavy rider - 70 kg.
I'm using the Shimano XT8000 cranks with an absoluteBlack 34 oval.

 

[PuddleDuck]

Hey, thanx for the reply!
The derailleur hanger is 100% alright. What kind of spacer are you talking about?
Actually, the rub is only present when I'm on the trail and when I'm on the bike. When the bike is on the workstand - there is no rud I can hear or see. I am not a heavy rider - 70 kg.
I'm using the Shimano XT8000 cranks with an absoluteBlack 34 oval.

I'm thinking of these types of spacers:
https://www.amazon.com/Wheels-Manufacturing-1mm-Cassette-Spacer/dp/B0025UINFC
https://www.evanscycles.com/shimano-1mm-hg-cassette-spacer-EV220571

To see which spoke(s) is/are rubbing you could mark the spokes with the likes of chalk or whiteboard markers, or whatever else will easily rub or clean off.

For the sake of absolute clarity, are you saying that you've aligned the der hanger with a an alignment tool?

If nothing else worked, you could "mis-align" the hanger in the vertical plane to the extent that the the mech no longer hit the spokes, and see how the shifting was....

 

[Ixaxaar]

I'm thinking of these types of spacers:
https://www.amazon.com/Wheels-Manufacturing-1mm-Cassette-Spacer/dp/B0025UINFC
https://www.evanscycles.com/shimano-1mm-hg-cassette-spacer-EV220571

To see which spoke(s) is/are rubbing you could mark the spokes with the likes of chalk or whiteboard markers, or whatever else will easily rub or clean off.

For the sake of absolute clarity, are you saying that you've aligned the der hanger with a an alignment tool?

If nothing else worked, you could "mis-align" the hanger in the vertical plane to the extent that the the mech no longer hit the spokes, and see how the shifting was....

Actually I used no derailleur allignment tool, but I'm pretty sure the hanger is alright as it shifts like butter through all the gears. It shifts better than my 2x11 XT drivetrain indeed.
According to absoluteBlack td chainline is 49.

 

[PuddleDuck]

Hi Ixaxaar,

I'll repeat what I said in my first post. Check that the der hanger is properly aligned. You need to KNOW that it is verses THINKING that it is.

If you look at any of many threads here on MTBR about shifting problems. The two things two check first are likely to be (1) der hanger and (2) replace the cable and housing. If the der hanger isn't in the correct position then there isn't a baseline from which to diagnose anything else. This is especially true of 12 speed, which is very sensitive to set-up.

Here's an article that compares various tools.
https://cyclingtips.com/2016/08/best-bicycle-derailleur-hanger-tool/
I use a basic one, which does have a little play, but provided I use the same process at each measuring point, it works well.

Let us know how you go.

As I mentioned once in my first post, I think that this slight rubbing is a slight safety issue - with some combination of frame flex &/or suspension compression and/or sticks getting stuck and/or your mech cage being bent and/or the hanger getting (furhter) misaligned, your set-up is much more likely to have the derailleur fully involve itself in your wheel. This never ends well, and least you'll end up with is walking your bike and a non-trivial repair bill.

I was asking about chainline for my own interest, it shouldn't have anything to do with the mech rubbing on the spoke(s).

 

[Ixaxaar]

I’ll go to the bike shop and see if the der hanger is alright, I am not sure if they have this tool. Very interesting article indeed.
Cables and housing are brand new as well as everything else, so I don’t think the problem is there. Might be the der hanger, I should buy a spare anyway.

 

[Ixaxaar]

Fixed it with the limit screw it was set too far by the spokes, just a slight turn and it works like magic now. How did I not came with this earlier :lol:

 

[PuddleDuck]

Fixed it with the limit screw it was set too far by the spokes, just a slight turn and it works like magic now. How did I not came with this earlier :lol:

Glad that you got it sorted

 

[stackveteran]

This is an amazing thread. Thanks for being a shining light. I'm doing something similar.
https://forums.mtbr.com/drivetrain-shifters-derailleurs-cranks/hybrid-shimano-sunrace-1x12-drivetrain-conversion-1135057.html#post14710143

I still have two questions. The first relates to the chain line. What is your chainline? You mention an oval chain ring. What chainline does it give you?

I'm fitting an SLX crank with a chainline of 52mm but the Absolute Black chainlink is dished and drops that to 51mm. I was thinking of moving the chainline another 2.5mm by repositioning one of the 2.5mm bottom bracket bushes to the ND side.

My second question is more theoretical. You mentioned how you were not able to get a good shift by following Shimano's alignment mark.
I'm trying to understand the reason. I thought if they are both 51 teeth sprockets their OD would be the same. Isn't that ultimately what matters that the chain can clear the teeth properly ? I'm not questioning you just trying to understand why the Shimano and Sunrace cassettes would behave differently.

 

[Harold]

My second question is more theoretical. You mentioned how you were not able to get a good shift by following Shimano's alignment mark.
I'm trying to understand the reason. I thought if they are both 51 teeth sprockets their OD would be the same. Isn't that ultimately what matters that the chain can clear the teeth properly ? I'm not questioning you just trying to understand why the Shimano and Sunrace cassettes would behave differently.

Clearing the cogs is only PART of the b-screw adjustment. The idea is that you're adjusting the b-screw so the chain matches the profiling of the cassette teeth optimally, too. There are lots of little things that need to line up right. The Shimano cassette and the Sunrace cassette are not exactly identical in all ways, so it makes sense that you might need to adjust for them subtly differently.

 

[Ixaxaar]

I already consider myself a fine specialist concerning the drivetrain, I managed to get it work smoothly as a normal shimano xt cassette, but that was achieved within two months of almost everyday struggle with the damn thing.
I own the cassette since december last year.
So basically, you have to lower the cassette a bit under the mark and then fiddle with the limit screw until it shifts perfect.
I must add, that you have to fine tune the system once in a month, but it is alright. I am by no means a fine mechanic,so if I can do it - you can do it. Just need to be patient and be careful, becouse the derailleur is very sensitive to the smallest change you make with the limit screws.
It works even better now, some months after the chain and cassette have broken in together.
As for why although identical cassettes, I think the guys from Sunrace made their cassette slightly different due to patents and stuff. I am sure the can make total replica of this cassette, but then they might get sued from Shimano becouse of patents. And it's up to the dear customer to find out how the damn works best. They could've at least done that, but anyway...I hope you sort out the things.
Make sure to use the Shimano 12 speed chain as it is specific and the cassette was made to work best with it.
Good luck and if you have more questions - hit us