Sorting XT M8000 chainline – an over engineered solution

I bought an XT 1×11 drivetrain in the CRC sale a month or so ago, and was surprised by just how bad the chainline is. I was annoyed by both the noisy running in bottom gear as the chain comes on and off the chainring teeth, and also the chain dropping down the cassette when back pedaling.

If you do the sums, a 50mm chainline at the front lines up with 8th gear at the back, so you’re crossing 7 gears to get to 1st but just 3 gears to get to 11th:

I think this a combination of Shimano doing 11 speed by dishing the extra sprocket over the spokes (effectively reducing rear chainline) and keeping the front wide to avoid clearance issues, but the end result is pretty lousy compared to the 1×11 on my CX bike.

I have loads of clearance at the front, and the chainring mounts to the inside of the spider, so I figured I’d space it in a bit to even things up. The obvious answer was a bunch of M8 washers and some longer bolts, but I struggled with the ugliness of round washers and big gaps on my shiny new chainset, and somehow came up with the idea of getting some custom spacers laser cut:

The spacers are 4mm which is equivalent to just over one sprocket putting it round about 7th gear. Chainring noise in 1st is much better, the chain no longer drops when back pedaling, and it looks much neater than washers or round spacers.

The unit cost of getting four done was fairly silly, but the marginal cost was pretty low. So I got a load more done at the same time in case anyone else is as obsessive as me.

The only issue is that the laser cut finish is pretty rough and needs quite a bit of finishing to tidy up (yes, I’m aware it’s mad to spend this much effort worrying about the appearance of a chainset on a 7yo mountain bike that I can’t even be bothered to clean properly)

I’m currently toying with ways to tidy them up quickly, and might have a go at getting some anodised black, but in the meantime if anyone wants some of the unfinished items I’ll post 4 for £6. I have plenty 🙂

They do need longer bolts. 4mm spacers work nicely with 16mm bolts which I had lying around from my old double+bash.

Good post!
I’m just about to put this drivetrain onto my Mega as an upgrade to the 10sp SLX.
PM me about the spacers – I’d be interested in a set.

Good work, and great attention to detail/OCD 😀

Good job.

Does anyone know if the XD driver solution result in a better chain line? I.e. is an XD cassette further to the right relative to the spokes?

I’ve found that you cna fix the backpedalling issue by reoving the XT cassette and fitting an xd driver and cassette, no other tweaking needed

Nicely done sir.

My default position on modern chainline is to push it as far in as the chainstay allows.

I’ve never been too OCD about the spacers though.

Scienceofficer – Member

….. as far in as the chainsaw allows.

Remind me not to hire you for bike maintenance purposes

Nice, I like that. Now if only you could’ve anodised them smoke black you’d be on to an absolute winner

My default position on modern chainline is to push it as far in as the chainsaw allows.

Yeah, I could quite happily go another 4mm and be pretty much bang on centre at the back and that’s without taking a chainsaw to the stays 😯 At some point you’ll start catching 10th gear when you’re in 11th

Now if only you could’ve anodised them smoke black

Watch this space…

Replace the frame and the wheels, for one that’s Boost148 at the back but still conventional bottom bracket?
That should gain another 3mm relative chainline.

This is bloody brilliant.

I am very interested if the OP commissions another batch in smoke black. I have two XT equipped full suss bikes, dropping the chain on the cassette really does get old.

Well done OP, I’d like to buy you a beer.

What size is the chainring? All of my shimano ones (34 and 36) came with spacers in the pack. Also I’ve noticed Shimano chains don’t seem to have these issues.

Nice solution, although why is the chainline so off in the first place? Is it because it is an older frame?

Going to check my chainlines later…

Did the same thing with cheap as chips alloy split washers, about 4 mm in using the original bolts!

Were free and are hardly noticeable behind the spider. Although that won’t be the case for all cranksets.

Small details and all that, good effort that man.

you could have just swapped the bb spacer to the other side of the frame…. just saying.

also, xt 11-40 and 11-42 cassettes are not 1 by specific, thats why they drop the chain when back pedalling. the 11-46 is and doesn’t drop the chain.

you could have just swapped the bb spacer to the other side of the frame…. just saying.

not great if you’re running clipless pedals as it throws your feel slightly out of alignment with your hips. I found it noticable even on flats (that feet weren’t evenly space on padals)

An added bonus of spacing a chain ring in, usually means you can use the original chain ring bolts, when converting older non 1x cranksets!

Nice solution, although why is the chainline so off in the first place? Is it because it is an older frame?

Don’t think so, I think it’s by “design” – there have been a few threads on here about it. You get the same chainline with 142mm (which despite being wider puts the cassette in the same place) and with boost, which is 3mm wider at both ends. As noted above, boost rear with non-boost chainset gets you a better chainline.

you could have just swapped the bb spacer to the other side of the frame…. just saying.

Aside from the OCD issue of knowing that my pedals were offset, even if I couldn’t feel it, it only buys you 2mm which is half a sprocket.

What size is the chainring? All of my shimano ones (34 and 36) came with spacers in the pack. Also I’ve noticed Shimano chains don’t seem to have these issues.

Interesting. Is it M8000? Did it include longer bolts? That is a Shimano chain – I have read that SRAM chains are less prone to jumping down, but it’s not going to change the fact that it’s running a silly chainline, with associated wear.

Is it M8000? Did it include longer bolts?

All mine are XTR. Chainrings don’t include bolts, the (XTR) chainset had the bolts of the correct size included though.

Interestingly looking at si.shimano.com the XT ones don’t show spacers, and you don’t get a 36t option either. FWIW the XTR spacers are nicely colour coded so don’t look out of place, but you’d need to get a bit more spendy…

ooh, looking at the XTR exploded view there is a Shimano part number of SM-CRM90 or Y1PV98030 for the spacers.
http://si.shimano.com/pdfs/ev/EV-FC-M9000-3775A.pdf
http://si.shimano.com/pdfs/ev/EV-FC-M8000-3849B.pdf

and here they are for sale, £10.99 for 4
https://www.sjscycles.co.uk/chainsets/shimano-xtr-fcm9000-gear-spacers-34t36t-only-y1pv98030/

also, xt 11-40 and 11-42 cassettes are not 1 by specific, thats why they drop the chain when back pedalling. the 11-46 is and doesn’t drop the chain.

What makes a casette 1X specific ?

I fitted the same crankset (34T) to my 2015 Anthem & was initialy concerned with the chainline. In reality its not to bad , it does skip down 1 on the largest sprok if back pedalled a full rotation but that is all.

I thought about swaping the spacer on the Presfit BB to the Left side , but after putting some miles on it I’m quite happy. Wouldnt say its any noisier at the extremes than the GX 1X11 on my Cove.

I do like the 1 X 11 setup a lot.

Smart looking solution. I’ve been running these on my older XT 780 chainset…

http://www.ison-distribution.com/english/product.php?part=CRIDSD06

What makes a casette 1X specific ?

I believe its the profiling of the largest sprockets teeth so that it can run at a more extreme chainline that 1x setups require. the 11-40 and 11-42 are designed to run in 2 and 3x setups so don’t require the additional profiling.

I’m not sure I buy that. Shimano list the 11-46 as 1×11, the 11-42 as 2/1×11 and the 11-40 as 3/2/1×11, so in theory the 42 and 40 are both designed to work with 1x. If there was some important difference in tooth shape, you’d expect Shimano to list them as “B-grade compatible” or whatever they call it.

A 1x setup doesn’t require a particularly extreme chainline. My SRAM CX setup has a front chainline of about 44mm, and the rear chainline is actually slightly wider than the MTB equivalent thanks to smaller sprocket pitch on road stuff with the result that it’s bang on the centre of the cassette. This works unsurprisingly well, and you probably see worse chainlines on 2x even without using big/big or small/small.

Obviously chainring/chainstay clearance is more of an issue on MTBs thanks to wider tyres but as far as I can tell, neither the M8000 cranks nor chainring are 1x specific, so you get the same chainline as the outer of a 2x.

Shimano list the 11-46 as 1x only. The others are compatible with both. I’ve had all 3 and the 11-46 is the only one that doesn’t derail when back pedaling.

They’ll all work pedaling forward with a 1x setup, the 11-46 is the only one designed specifically for 1x.

Ok, this might be a silly question, and will only work if you have clearance on the frame to do so….

Is there any reason why you couldn’t just move the BB spacer to the other side of the BB shell? This would give you about 2.5mm of movement to the left, reducing the need for spacers as thick.

he’s already responded to that question. It’s further up ^^^

They’ll all work pedaling forward with a 1x setup, the 11-46 is the only one designed specifically for 1x.

I don’t doubt your experience with it, but I’d be very interested to know how it’s different. My reading is that Shimano just say that it won’t work with 2x or 3x, and that the 11-42 won’t work with with 3x, not that the 11-46 is actually better for 1x than the others.

Is there any reason why you couldn’t just move the BB spacer to the other side of the BB shell? This would give you about 2.5mm of movement to the left, reducing the need for spacers as thick.

No harder to add a 4mm spacer than a 2mm one, and avoids putting the chainset off-centre.

D’oh! I missed that, and explains the slightly weird feeling that I got yesterday when I took the bike out to slosh the sealant around following a tyre change.

Off to spacers for me then!

Before switching my Instinct to 1×11 (from 2×10), I looked at a few videos on youtube to see if there were any issues like this – some fella found his chain jumped down the sprockets when back pedalling, so he tried different brands of chain and found some better than others (can’t remember which now).
Anyway, I swapped everything over, tried it and it was perfect straight away. It must depend on your frame’s stay alignment as well as chain/cass/crank combo.

I found several people claiming that SRAM chains work better. I think the main variables are chainstay length and chain tension, as the other dimensions (BB width and cassette position) should be the same.

the chain dropping down the cassette when back pedaling.

If you stopped back pedalling, which I don’t know why you’d wish to, the worst of your problems would be solved..

@PDW, i’ll have a look tonight to see if i can spot any difference. or if i get chance i’ll pop into the shop and have a look.

Just found this page on the OneUp website which might help people (UNDERSTANDING CHAINLINE FOR OPTIMAL 1X CONVERSIONS (BOOST AND NON-BOOST))

Yeah, I came across that page when I was looking into the problem originally, along with various posts from OneUp in other forums. They seem to agree that the stock chainline is too wide, although seem to recommend only going to 48mm or 49mm, I think on the basis that you spend more time on the outer sprockets (and fewer teeth means faster wear)

This still seems high to me. Even at around 46mm, it’s still biased towards the higher gears, and that seems to be about the point at which mine starts running quietly in bottom gear. 46mm is still wider than road/CX 1×11, where you’d think usage is more biased towards higher gears.