[trel]

Wolf Tooth describes their Shimano direct mount chainrings as "BOOST (52MM CHAINLINE / 3MM OFFSET)". So I think a 3mm offset on Shimano direct mount chainring on a M8100/M7100 crankset results in a 52mm chainline.

Direct Mount Chainrings for Shimano Cranks

Direct Mount Chainrings for Shimano Cranks. These chainrings are for Shimano cranks. The Wolf Tooth chainrings feature our patented Drop-Stop® design for the best wear life, chain retention and mud clearance.

www.wolftoothcomponents.com

This means that the 3.6mm "custom offset" that Garbauk provides, would result in a 48.4mm chainline. But your mileage will vary, depending on whether you have any BB spacers.

The impact of BB spacers can be a little tricky to figure out. For example, my frame has a 89.5mm BB shell. This is coupled with a BB92 press-fit BB. To fill out the 92mm BB width, a 2.5mm spacer is added to the drive side. This in turns increases the effective chainline by 1.25mm. Why 1.25mm and not 2.5mm? That's because, in a perfect world, a 1.25mm spacer would be added to both the drive and non-dive side to perfectly center the BB. However, a single spacer is used for convenience by manufacturers.

Concerning the chainline at the BB, I've got a very similar spec to yours. I used to have a Shimano BB MT800-PA, 2.5mm spacer DS. Swapped spacer to NDS for chainline.

Now with PF4130, I had a 2.5mm spacer on the NDS, then over time the NDS cup came out of the shell ~ 1mm. I didn't want to use retaining compound on the composite BB shell so I removed the spacer, reinstalled with grease as usual, used spindle spacers instead and had no problems.

Had a quick recheck-
PF BB92 / 89.5mm wide, 41mm ID, composite BB shell/frame.
No BB spacers, 2.5mm NDS Spindle spacer, 1mm DS Spindle spacer, RF preload adjuster takes up the rest.
Crank spindle is where you'll easily make up a few mm. You might be better off using something else rather than the shimano cranks, but you might get it working nicely with them.
Offsetting the cranks with spacers obviously changes the pedal spacing too. You may not notice or care. It does feel a bit off to me so i tried to keep them even as possible.

 

[bayposter]

Well, I finally heard back from OneUp. They said that Shimano sets the chainline with the crankset and that they don't provide any offset to compensate. I'm guessing that they, unlike Garbaruk, think there's not enough demand out there for an offset ring.

Wolf Tooth doesn't seem to provide any non-boost options for Shimano direct-mount chainrings, either. In contrast, they have a non-boost option for SRAM direct-mount chainrings with their CAMO spider.

CAMO Direct Mount Spider For SRAM 3-Bolt Cranks

The CAMO chainring system was created by the Wolf Tooth engineers for Chainline And Material Optimization on direct mount style Chainrings. The key advantages include: Perfect chainline, optimal material usage, less expensive replacement chainrings, fast chainring swapping and color.

www.wolftoothcomponents.com

I think part of the problem is that Shimano markets the M8100/M7100 crankset as both boost and non-boost compatible. But I'm not sure I buy it. I've experimented with a 52mm chainline on a non-boost frame. The chain angle on the largest cog is pretty extreme. A 48-49mm chainline looks much better.

 

[jrob300]

I think part of the problem is that Shimano markets the M8100/M7100 crankset as both boost and non-boost compatible. But I'm not sure I buy it. I've experimented with a 52mm chainline on a non-boost frame. The chain angle on the largest cog is pretty extreme. A 48-49mm chainline looks much better.

I think from Shimano that's, "Ok, Boomers.... you refuse to buy into the newer, cooler Boost technology? Well, that's fine, we're gonna sell you a one-size-fits-all crank, that doesn't". I'm beginning to wonder if I made a mistake staying with Shimano.

 

[newnuj]

Wolf Tooth doesn't seem to provide any non-boost options for Shimano direct-mount chainrings, either. In contrast, they have a non-boost option for SRAM direct-mount chainrings with their CAMO spider.

CAMO Direct Mount Spider For SRAM 3-Bolt Cranks

The CAMO chainring system was created by the Wolf Tooth engineers for Chainline And Material Optimization on direct mount style Chainrings. The key advantages include: Perfect chainline, optimal material usage, less expensive replacement chainrings, fast chainring swapping and color.

www.wolftoothcomponents.com

I think part of the problem is that Shimano markets the M8100/M7100 crankset as both boost and non-boost compatible. But I'm not sure I buy it. I've experimented with a 52mm chainline on a non-boost frame. The chain angle on the largest cog is pretty extreme. A 48-49mm chainline looks much better.

52 mm chainline on non-boost frame - What chain ring were you running?

 

[bayposter]

52 mm chainline on non-boost frame - What chain ring were you running?

Like I said, this was just an experiment. I put a 12-speed freehub on a non-boost frame with a 2x10 Shimano M785 crankset. The outer ring on that crankset has a chainline of about 52mm. I threaded a 12-speed chain and just eyeballed the chainline but didn't ride the bike.

On the biggest cog, the chain angle looked very extreme. It was definitely worse than when the chain is on the big cassette cog and outer chainring on the 2x10. The 12-speed cassettes are about 2mm wider and extend inward, so this is not surprising.

 

[bayposter]

I emailed Wolf Tooth and asked whether they planned to offer more offset options for their Shimano CAMO spiders. Here is their reply.

"Thanks for checking in with us. Shimano is no longer offering a 49 mm chainline crankset option. The new tooth profile and chain are versatile so the 52 mm chainline is used for both. At this time we do not have plans to offer a 49 mm option as our tooth design has been designed similarly and is chain line tolerant."

I can certainly understand Shimano's position -- why make a crankset for the small (and shrinking) market for 12-speed drivetrains on non-boost frames? That would probably be a money loser.

But no one can convince me that a 52mm chainline is optimal for a non-boost frame. A non-boost hub is offset 3mm inward compared to a boost hub. So all things being equal, the chainline of the crankset should be adjusted by the same amount.

 

[jrob300]

I emailed Wolf Tooth and asked whether they planned to offer more offset options for their Shimano CAMO spiders. Here is their reply.

"Thanks for checking in with us. Shimano is no longer offering a 49 mm chainline crankset option. The new tooth profile and chain are versatile so the 52 mm chainline is used for both. At this time we do not have plans to offer a 49 mm option as our tooth design has been designed similarly and is chain line tolerant."

I can certainly understand Shimano's position -- why make a crankset for the small (and shrinking) market for 12-speed drivetrains on non-boost frames? That would probably be a money loser.

But no one can convince me that a 52mm chainline is optimal for a non-boost frame. A non-boost hub is offset 3mm inward compared to a boost hub. So all things being equal, the chainline of the crankset should be adjusted by the same amount.

OneUp told me pretty much the same thing and agreed that the Garbaruk would be the best option for this application.

 

[newnuj]

Like I said, this was just an experiment. I put a 12-speed freehub on a non-boost frame with a 2x10 Shimano M785 crankset. The outer ring on that crankset has a chainline of about 52mm. I threaded a 12-speed chain and just eyeballed the chainline but didn't ride the bike.

On the biggest cog, the chain angle looked very extreme. It was definitely worse than when the chain is on the big cassette cog and outer chainring on the 2x10. The 12-speed cassettes are about 2mm wider and extend inward, so this is not surprising.

Shimano 12s chain rings are specifically designed to fit both boost and non-boost chain lines. M785 chain rings are not.
So although it looks like extreme chain angle, it is no problem.

To quote my favourite Astrophysicist Dr Neil deGrasse Tyson, "The good thing about science is that it's true whether or not you believe in it.".

 

[bayposter]

Shimano 12s chain rings are specifically designed to fit both boost and non-boost chain lines. M785 chain rings are not. So although it looks like extreme chain angle, it is no problem.

I've been waiting to convert a non-boost bike to a Shimano 12-speed drivetrain because I was missing some parts. But I've gathered all the parts now, including a Wolf Tooth hyperglide+ chainring and some chainring spacers to tweak the chainline. So I'll probably do the conversion soon.

The chainline without any spacers is about 52mm, whereas it's about 49mm with the spacers. So by adding/removing the spacers, I can compare the performance of the two chainlines. I'll try both and report back.

 

[jrob300]

I've been waiting to convert a non-boost bike to a Shimano 12-speed drivetrain because I was missing some parts. But I've gathered all the parts now, including a Wolf Tooth hyperglide+ chainring and some chainring spacers to tweak the chainline. So I'll probably do the conversion soon.

The chainline without any spacers is about 52mm, whereas it's about 49mm with the spacers. So by adding/removing the spacers, I can compare the performance of the two chainlines. I'll try both and report back.

That would be awesome.... the Garbaruk chainring with shipping is $97 US. I'd rather not do that again.

 

[bayposter]

That would be awesome.... the Garbaruk chainring with shipping is $97 US. I'd rather not do that again.

Although I don't plan on buying a Garbaruk chainring right now, I emailed them and they sent me the chainlines provided by their Shimano direct-mount "Custom Offset" chainrings. Here's the table they sent:

Shimano XT7100/8100, XTR 9100 Round (Custom Offset)
28t, 6.4mm offset, 48.6mm chainline
30t, 6.4mm offset, 48.6mm chainline
32t, 6.4mm offset, 48.6mm chainline
34t, 5.9mm offset, 49.1mm chainline
38t, 3.9mm offset, 51.1mm chainline

You can work backwards from these numbers and see that a 3mm offset provides a 52mm chainline, so that must be what Shimano is using. I think the offset is relative to the mounting point.

The Garbaruk website is definitely confusing. It only lists the "Shimano XTR M9100 Round (Custom Offset)" chainring, but the table they sent seems to imply that they also have a custom offset chainring for the M7100/M8100. This seems to be the chainring they sent arnea. I sent a follow-up email for further clarification.

I also asked about the Garbaruk Shimano direct-mount chainrings without the custom offset. The description mentions variable chainline technology (VCLT) for these but the chainline is always the same.

Shimano XT7100/8100 Round
all sizes, 3.3mm offset, 51.7mm chainline

 

[jrob300]

Although I don't plan on buying a Garbaruk chainring right now, I emailed them and they sent me the chainlines provided by their Shimano direct-mount "Custom Offset" chainrings. Here's the table they sent:

Shimano XT7100/8100, XTR 9100 Round (Custom Offset)
28t, 6.4mm offset, 48.6mm chainline
30t, 6.4mm offset, 48.6mm chainline
32t, 6.4mm offset, 48.6mm chainline
34t, 5.9mm offset, 49.1mm chainline
38t, 3.9mm offset, 51.1mm chainline

You can work backwards from these numbers and see that a 3mm offset provides a 52mm chainline, so that must be what Shimano is using. I think the offset is relative to the mounting point.

The Garbaruk website is definitely confusing. It only lists the "Shimano XTR M9100 Round (Custom Offset)" chainring, but the table they sent seems to imply that they also have a custom offset chainring for the M7100/M8100. This seems to be the chainring they sent arnea. I sent a follow-up email for further clarification.

I also asked about the Garbaruk Shimano direct-mount chainrings without the custom offset. The description mentions variable chainline technology (VCLT) for these but the chainline is always the same.

Shimano XT7100/8100 Round
all sizes, 3.3mm offset, 51.7mm chainline

Shimano offset is indeed 3mm. The only 7100/8100 ring they offer in more than a 3mm offset is the oval. Don't ask... I've been round and round with Garbaruk the last week and turns out that chainline is a little understood attribute.... I have a 9100 custom offset on order.

 

[bayposter]

Shimano 12s chain rings are specifically designed to fit both boost and non-boost chain lines. So although it looks like extreme chain angle, it is no problem.

Found the post below in another thread from somebody who set up the full XT 12-speed drivetrain on a non-boost frame.

"I installed the full shimano XT 1x12 set up on my bike, 142mm rear end and bb92 pressfit BB... Although the pedals are fine and equal across the width of the bike, the chainline is too far outboard."

49mm Chainline on Shimano 12sp cranks

Is there anyway to acheive a 49mm chainline with Shimano 12sp cranks? I am doing a Shimano 12sp build on a frame with a 135mm rear end. I have the mounting of the cassette figured out on the DT240 hub leaving tye crankset to figure out. Worse case i can run SRAM Dub crank with an One One...

www.mtbr.com

 

[Schmalejandreau]

Hey, all!
This Chinese contraption should do it, or so the manufacturer says. Someone could try this to see if they get a 49 mm chainline with this.

https://www.aliexpress.com/item/1005004966637035.html