I haven't found any issue with rear shifting due to chain line as shifting is governed by where the jockey wheels are independent of chain line. Chain line affects how the chain feeds off the cassette and onto the rings (or the other way around backpedaling) , so front shifting can be affected. For 1x boost, I like to use 50.4. Wolf Tooth has a white paper on the subject on their website. You do need to check for clearance between the ring and the chainstay.

 

you reference exactly what made me think of this with wolf. it made me wonder if the out spacing had more to do with fitting 32-34-36 t sprockets rather than what would be optimum chainline. as long as you have clearance, according to them a 50.4 would be better to run even on a boost bike vs 52-56 which the vendors tell us we need on boost bikes. in my case i'm looking to run 30t on a 1up'd 11-45 cassette. it sounds like as long as the chainring fits i would be better off using the 50.4 on boost.

 

I have both a boost Mojo3 and Ripley. Better chain line with a 1up or AB ring that corrects the chain line to 49mm.

It does limit the size of the ring, but that is very frame dependant. I had a 32t oval on the Mojo3 but can only fit a 30t oval on the Ripley.

 

thanks guy. you pretty much reinforced what i already suspected about the "must have boost cranks on boost frame" mantra.

 

I have a WolfTooth ring that corrects the chainline by 2mm and it shifts better than the Shimano single I had.

 

OP, you are absolutely correct in your thinking and it's not a mantra, it's utter BS, 46.5/47mm chainline always worked best with a 135/142 rear, the newer 50-51 chainlines brought on by external BB cranks always gave bad chainline. I run a 150x12 rear and use my old 9spd M760 XT crank with a 51mm chainline and it just about lines up perfectly with the middle of the cassette. As you said, only reason to maybe go wider is to accommodate a bigger ring and for tyre clearance.

 

OP, you are absolutely correct in your thinking and it's not a mantra, it's utter BS, 46.5/47mm chainline always worked best with a 135/142 rear, the newer 50-51 chainlines brought on by external BB cranks always gave bad chainline

I've thought this exactly. The external BB -- with the 2.5mm driveside spacer -- moves the ring too far outward for ideal shifting, especially as you shift on to the larger cogs.

My thinking is it's a holdover from the 2x and 3x days and is less than ideal for today's 1x setups. The pf BBs, even though they may have their own issues, seem to be inherently better for chainline as they're even on both sides.

Wheels Manufacturing make great spacers where you can break up the needed 2.5mm. Currently I have 1.8mm on the drive side and 0.7mm on the non drive side and have been really happy with that. Switching that may make it even better. Granted this is fine tuning but every single bit helps if you're looking for perfect shifting.

Overall, definitely avoid boost crank if it can be helped, as chainline is not as good. As others have said here, only reason to go that route is if it's needed for clearance.

I've played around a fair bit with chainrings and cassettes (plus expander cogs) trying to perfect shifting through the range. I'm very happy with my current setup, FWIW:

XTR non boost trail cranks with WolfTooth ring. I've found the WT and AB rings work better than OneUp -- moving the ring 1-1.5mm more inwards

XT 11-46 cassette. Best yet. The XT 11-42 with OneUp 45t was very good but the 11-46 is even better.

Also XTR gs rear derailleur. KMC gold chain. And the spacers on the BB. Hope that helps.

 

wolf even wrote me back saying basically the same thing and brought up something i had not thought of. fat tires also would require outboard spacing

Hey Kyle,

Thanks for the note. We have a chainring made specific to the XTR 9020 crank. /96-mm-bcd-chainrings-for-shimano-m9000/9020 Our 30t ring will sit at 49 mm chainline. The 36t rings because of the larger radius are made to sit at 50 mm chainline to assist in clearing the chainstay.

We have a tech page that explains /boost-chainline-and-chainrings. Our boost chainrings sit 3 mm further outward than our standard rings, primarily for chainstay clearance when using larger rings on boost spaced bikes or for clearance when using tires greater than 2.8.

Let me know if I can assist.

 

haven't. it's 440-450g on average. if they made a lighter version i may but the xtr 11-40 with the 45 conversion keeps the gear ratios really tight across all 11. using the 45t on a 42t cassette might is such a small leap. also adds even more weight. at least with the 47t you get a substantially lower gear. also it's the 18t that gets added as you subtract the 17t and 19t from the stock shimano cassette.

 

Mine was closer to 430-440 gram range.

As someone who has actually used all these combinations, and with multiple chainrings -- OneUp 30 and 32, WT 30 and AB 32 oval -- I can tell you (and I guess more importantly others here who may be interested in the best possible shifting out of Shimano) that this set up is by far the smoothest, most refined, fastest and most quiet I have tried. Across the entire range. Up and down the cassette. Zero back pedalling issues too.

Also, while the WT/OneUp solution was a great temporary solution, you sacrifice the even spacing in the high end gearing because of the need to remove the 17t and 19t. It's definitely fine -- but it's not as good as stock.

 

I'm using 30T Rotor QX1 oval ring with a Garbaruk 11-50T cassette with their extender arms on what was a XTR med cage 11s rear derrailleur and XTR 11s shifter. Shifts great with m9000 crankset. B tension is not maxed out. Chain length is sensitive to be correct for good shifting. Might do the same to a second bike soon. I tried to put a 47T oneup on a XTR 40T cassette and they didn't line up right for the chain to engage on 2nd cog. Garbaruk doesn't have the added cogs, 37-46 gap, and its lighter than XTR. Probably the same with the derailleur mod. Have also spoken with a US Rotor distributor who said AB rings are same oval pitch as Rotor rings in position 3 which is what I use, and they are cheaper and don't require proprietary spider. That will be my next oval purchase.

I just received a m9020 Boost crankset which i'm hesitant about because the Q factor is wider than it needs to be, so I ended up on your thread. Can't you use offset rings to achieve the same chainring position on either crankset? Maybe there aren't many options there...