[jrob300]

Edit thread to reflect that the real issue was upgrading a non-boost frame to Shimano 12 speed due to minimal support for non-boost chainlines.

I have a 2016 Scott Genius. It came with an XT8000 2x crank, but has been converted to 1x11. I would like to upgrade to XT 1x12 so I can run a 28t. I'm looking at the cranks and they come with 3 different Q factors. I'm confident that this affects chainline, which I guess I should be concerned with, but I'm not sure which one is correct for my application.

Anybody here a drivetrain expert?

 

[jrob300]

What chainline does your bike use now? Regular? Boost? Superboost?

For Shimano's purposes, they spec 52mm chainline for regular and most boost applications. 55mm chainline is a wider chainline that some manufacturers are using (not always in the same way) for clearance reasons. The 56.5mm chainline is the one for superboost.

Shimano DOES link different q-factors with different chainlines for simplicity's sake. Because typically the reason you need wider chainlines is because the chainstays are wider, so you ALSO need a wider q factor for clearance.

You'll likely be able to achieve different chainlines on a given crank by using aftermarket rings. What matters will be the offset of Shimano's rings and how they differ from aftermarket ones, which mostly use SRAM's 0, 3, 6mm offsets. I don't know the exact answers there. I just make this comment because Race Face handles chainring offsets the same way (all their rings are the same offset), and using aftermarket rings gives different chainline options than you get with RF's rings. Stands to reason it'll work the same for Shimano.

Not sure what the stock chainline was.... frame is 142mm+. The 178mm Q is 55mm chainline. 172mm is 52mm.... sounds like the 172 is what I want?

 

[jrob300]

As a side note, any reason for you not to just grab a 64BCD 28t NW chainrings instead?

Good info on the chainline.... funny enough, I just emailed them today and their chainring is only compatible with 12 speed SRAM and 11 speed Shimano. I am currently running an 11 speed Garbaruk 11-50 cassette and I'm not happy with the bailout jump from big gear to #2. The Shimano 12 speed cassette has tighter gearing down low and I'm prepping for a "gravel" race next year with a lot of stupid steep climbing all day long....

 

[jrob300]

If you want a 12sp Shimano's cassette, you are going to need a new microspline freebody for your hub.

Yup... factored in. New cassette. Microspline driver for DT350 hub. 12 Speed shifter. New XT crank/chainring and 12 speed chain...

 

[jrob300]

You could actually use your current crankset. Wolf Tooth makes Shimano 12-speed compatible chainrings for the FC-M8000. You can find these on Amazon.

On a non-boost frame like yours, you want a chainline of about 49mm. The FC-M8000 crankset has a chainline spec of 50.4mm for the outer chainring, but that's only if you use a 1x Shimano 11-speed chainring. These include tabs that offset the chainring by about 2mm. With a flat chainring, the chainline is about 52mm. The Wolf Tooth 30t chainring has similar tabs, but their 32-36t chainrings are flat and would require chainring spacers to get you to a 49mm chainline.

In contrast, the FC-M8100 crankset has a chainline of 52mm. Shimano claims that it will work on a non-boost frame. But the chain angle in the largest cog would probably be non-optimal, resulting in a noisy, less efficient drivetrain that wears out faster.

A lot of good info in this post. This is actually where I started... looking for a chainring for my current crank, but I was unable to find a 28T 12HD+ compatible ring that would fit. Wolftooth says they only make down to a 30T in Drop Stop ST, which is their 12HD+ compatible format.

Back to the drawing board.

 

[jrob300]

You could do all this with a Race Face crank or even a SRAM crank. It gets you direct mount, the ability to get a narrow non-boost chainline (though admittedly, the RF option is SO flexible that you have to run the math a million times to ensure you've got it right with the combo of spindle length and chainring offset).

I'm using a OneUp Switch spider to get a Shimano 12spd compatible 28t ring on my Turbine CINCH cranks. My bike specs a 55mm chainline (though I'm able to get away with a 53.5mm one with such a small chainring), so a little different than you. But with a diff spindle length and/or spider offset, you could get closer to optimal than Shimano 81xx allows.

This is probably the path I will pursue. I had seen that Switch and really liked it. It was my intent to use that with the XT8100 crank until I started looking hard at their chainlines.

 

[jrob300]

You might try asking OneUp about how a different offset on a Switch spider would change your chainline from stock on an 81xx crankset. I've never seen anywhere what the offset equivalent of the stock Shimano chainrings is. If you can find that as a baseline, and then adjust the stock 52mm chainline inboard 3mm by using a Switch carrier or regular chainring from another manufacturer with 3mm more offset, you COULD potentially hit the 49mm chainline, or at least closer to it.

Great minds... I emailed them with that question earlier this morning!

 

[jrob300]

Get 7100 or 8100 crank without chainring and Garbaruk custom offset 28t chainring (oval or round) and you will get 48.2mm chainline. Did it myself for non-boost frame and it works perfectly.

That would be easier than changing out BB. Does it support 12 speed HD+? NVM.... just found it on their site. Thanks!!!

 

[jrob300]

I don't see how you could adjust the 81xx chainline using the OneUp Switch. The Switch carrier requires a Switch chainring. But I don't see any Switch/Shimano chainrings with an offset. Nor does there seem to be any way to add an offset using a spacer.

But not having used the product, I could be wrong. Does anyone know for sure?

It's possible, like the Garbaruk, that the carrier comes with a non-standard offset. Garbaruk Just saw Harold's response....

I've emailed them to find out what the chainline is with their product, but no response yet. Right now the best bet looks to be Garbaruk and an 81xx crank, although I'm also looking into an NX Eagle DUB crankset with a BB86 to 30mm BB. Then use the Switch to install a 12 HD+ compatible ring. The Garbaruk solution is much simpler, but I am having a hard time finding the narrow chainline 81xx crank arms in stock anywhere.

 

[jrob300]

Updated thread title to reflect the fact that we're really talking about making Shimano 12 speed HD+ work with non-boost frames.

 

[jrob300]

We had this talk like month ago, all the details are in this thread:

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

Arnea,

Is this the SLX crank you used?

 

[jrob300]

No, I used FC-M7100. It has 6mm shorter spindle and will give you 3mm smaller chainline. Don't get FC-M7120 for non-boost frame.

I can't find a 175mm length/52mm chainline XT or SLX crankset or crankarms in stock anywhere reputable..... FC-M7100-1 or FC-M8100-1. If anyone stumbles across one, please post here.

 

[jrob300]

Universal Cycles has them I believe: Shimano FC-M8100-1 XT Crank Arms - 12 Speed
They are very reliable and have been in business for a long time..

Thanks so much for the tip!!! Ordered!!!

 

[jrob300]

My pleasure. BTW, on my non-boost KHS 7200 I'm running Shimano MT900 cranks which are the "black cranks" used as a stop gap until the XTRs were ready and they are basically the XTm8100 with different graphics. They work fine on the bike and are over out a bit due to 52mm chainline however the newer Shimano chains seem to have more ability to flex than 10 speed versions (never used 11-speed Shimano chains) so they cope. I get zero back pedal issues on this bike as well.

My chinline is 49mm with the XT8000 crank and I get back pedal drop issues now, but my understanding is that it is fairly normal with the Garbaruk cassette. I emailed Garbaruk last night regarding their offset chainrings. I post what they recommend, but it's good to know that I'm not stuck if all I can get is standard chainrings...

 

[jrob300]

My pleasure. BTW, on my non-boost KHS 7200 I'm running Shimano MT900 cranks which are the "black cranks" used as a stop gap until the XTRs were ready and they are basically the XTm8100 with different graphics. They work fine on the bike and are over out a bit due to 52mm chainline however the newer Shimano chains seem to have more ability to flex than 10 speed versions (never used 11-speed Shimano chains) so they cope. I get zero back pedal issues on this bike as well.

Which cassette and chain are you using?

 

[jrob300]

Deleted. Answered in another thread....

 

[jrob300]

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. So it comes down to the Garbaruk offset (I've emailed them with questions and no response to date) for a 48-49mm chainline, or anyone else's ring with no offset for a 52mm chainline.

 

[jrob300]

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 6.4mm "custom offset" that Garbauk provides, would result in a 48.6mm 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.

Wolftooth doesn't offer a 28T that I could find. Looking like it's Garbaruk or Garbaruk.

 

[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.

 

[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.