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I got a new frame recently (custom Alpkit / Sonder Broken Road). I have put my old drive chain on it (M8000 1x with OneUp 50t conversaion) which worked faultlessly on my old Surly Krampus Ops frame.
However, I simply cannot adjust it correctly. I can get it shifting perfectly on every cog except the smallest 11t one. Whatever I do, as soon as I put any real power through the drive train when on 11t, it will start jumping. I have tried tweaking the limit stops and cable tension.
This morning, I suddenly thought that my new frame is boost (rear wheel has a Hope Boost adapter for a non-boost Pro4 hub) and the crankset is non-boost.
This means that my chainline is 50mm, as opposed to the recommended 51-53 for boost. Could this be causing the 11t to jump?
If this is the case, does this mean I HAVE to get a new crankset, or is there something else I can do (seems insane to pay £100 to move the chainring by 3mm!)
Thanks!
Small cog slipping is often caused by wear - or by insufficient chain wrap. Try adjusting the B screw on the mech to improve the latter. It's possible that the mech is at a different angle on this new frame.
Edit : other than frame/chainset clearance a non-Boost crank will work fine on a Boost rear end.
If it's not wear, just buy a ring with a different offset. It seems most manufacturers have a slightly different offset built in to their rings.
I really hope it works, cos I accidentally bought a smaller chainring for my GF without remembering that her bike has this newfangled boost thing.
Oops.
It's only a 3mm difference in offset, so I personally can't see it making a huge difference as long as it doesn't hit the frame or cause chain to rub on the tyre.
No spacer on the bottom bracket you can move across to shift it over a bit?
I don't think it can be wear, as the cassette isn't that old, and was shifting flawlessly on the old frame a few weeks ago.
The b-screw is as tight as I can make it (because of the 50t converter, it has to be quite far out compared to a normal 42t max)
@scotroutes: What do you mean by the mech might be at a different angle? Is there something I can check / do on this? I presume you are implying that an offset chainring will work?
@TheGingerOne I didn't realise different offset chainrings was a thing; I have to admit, I am struggling to find one though... I can find lots of spacers to go from boost cranks to non-boost chainline (i.e. moving the chainring closer to the frame), but only one that goes the other way, and that is for SRAM, not the M8000 96BCD asymetric fitting. Any ideas? I did find this: https://www.probikekit.co.uk/bicycle-cranksets-and-chainrings/absoluteblack-xt-m8000/mt700-direct-mount-oval-mtb-chainring/11798831.html?utm_source=kelkoo&utm_medium=cpc&utm_campaign=kelkoo&affil=thgppc&switchcurrency=GBP&shippingcountry=GB&variation=11798834 ... but I am not sure if it the right thing
@tthew I don't think I can do anything with the BB spacing; I already have the requisite spacer on the drive side for a 73mm threaded BB... unless there is something clever I can do here?
Thanks!
my mates did this because he'd fitted the chain snap link upside down, it was an SRAM Eagle link or something.
Could you have done that?
Absolute Black - Chainring is not threaded but chainline is corrected to 49mm with use of built in spacers
One-Up - chainline 49mm (corrected from stock 50.4mm) for a quieter drivetrain with improved chain wear and best drop performance
So I assume the standard XT ring is a 50.4mm offset. If you need it 'further out', then the standard XT ring is going to be better than the other 2.
As an aside, when I fitted xt m8000 1x11 to my Yeti, the chain fell off both the big and small rings until I got the b tension adjusted, then it was fine. It sounds like you might just need to fine tune the B screw.
For an English threaded BB, the spacer can go either side of the bb shell if that helps to move the chainline.
What do you mean by the mech might be at a different angle? Is there something I can check / do on this? I presume you are implying that an offset chainring will work?
The bit of the mech hanger that the B screw fits against is subject to a lot of variation. Some set the mech at an odd angle (as viewed side-on). If you've adjusted it as best you can for the 50T then it could just be a compatability issue.
As above - non-Boost cranks should work just fine with a Boost rear hub.
the rear derailleur feeds the chain onto the cassette so at that point it should be dead straight and the chainline should be irrelevant, it really only comes into play at the point where the chain releases from the cassette at the top and at the lower jockey wheel.
If you are just using the B-screw to max the derailleur out so it clears the 50t then the chances are that the chainwrap on the small sprocket is less than ideal. I'd suggest trying out a hanger extender or looking at your hanger alignment, I doubt that moving the chainring a few mm (and the resulting degree or so of chainline change will make a difference.
Just to clarify where I said "As an aside, when I fitted xt m8000 1×11 to my Yeti, the chain fell off both the big and small rings until I got the b tension adjusted, then it was fine. It sounds like you might just need to fine tune the B screw.", what I actually meant and clearly didn't write at all!!!!!, was that the chain was falling off the inside of the chainring when in the big sprocket and the outside of the chainring when in the small sprocket, until I adjusted the b tension.
Obviously, different to your symptoms, but an idea of how the B screw has a surprising impact.
Thinking about it, it does sound like the chain is slipping on the sprocket as there isn't eough chain wrap around the cassette because of where you have to adjust the b screw to accommodate the 50t.
Ok, thats really useful info; thanks everyone... sounds like I can keep my £100 in my pocket :). I will go and have a tinker with the angle of the mech attachment and the b-screw.
Thanks! 🙂