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As above I’ve built a bike for my nephew and the chainline in the lowest (largest gears) is shocking. This means shifting is a bit dubious in certain parts of the cassette.
I’m checking the mech hanger this week but am wondering about changing the chainline on the bb / cranks.
I have a 135mm qr frame with a dub direct mount crank. I have a 6mm offset non boost chainring on there. It’s a 73mm she’ll so I currently have no bb she’ll spacers and a 4.5mm driveside crank spacer (the ones that clip into the face of the bb).
Once done up tight I’m needing to take up the slack with a few turns of the collar on the non drive side and hen it seems smooth / there’s no play.
Could I run a smaller spacer on the driveside and then put a small spacer on the non driveside to move the chainring further inboard? There’s no issue with chainring clearance of the chainstay and I don’t think that’ll put the crank arm too close to the chainstay either.
I’ve got a spare 2mm and 3mm spacers - if I put the 2mm driveside and 3mm non driveside and then take up the slack with the collar on the non driveside I’m wondering if this would cause any bb issues? It’s technically 0.5mm more of spacers but that seems a tiny amount and it’s not like a gxp bb where there’s a hard stop and you have to space it perfectly.
That's the correct chainline for DUB / SRAM as far as I can work out ? Are you sure it's a 6mm offset chainring ?
1x11/12 is always going to be a little bit compromised for chainline on the outer reaches of the cassette. You could *theoretically* use some alternative spacers to move it in by a few mm - eg my uberbike dub BB came with a 2.5mm and a 2mm spacer for the DS (one between frame and shell and one between bb and crank respectively) - you could move the 2.5mm across to the otherside; but then your cranks wouldn't be central anymore - though you might not notice a 2.5mm change...
Definitely a 6mm offset - said it on the packet and it’s noticeably dished more than a 3mm one.
I bought another dub bb figuring that will need a 4.5mm spacer for my new bike (boost rear end) but I should get a 2 and 2.5mm spacer with it. Wrong! It came with a 4.5 / 3 / 2 ffs.
I refuse to spend £12 on a lack of dub spacers when ideally I just need a 2.5mm on top of what I have.
Maybe I’ll give a 3 and 2 combo a go and see how it goes.
I very much doubt my nephew is going to notice the crank being 2.5mm further to the left.....
It might work; my worry would be that I wouldn't want to space the axle on the NDS; but you should space the axle on the DS - so you'll need a 2/3mm axle spacer and a 2/3mm shell spacer. I'm sure the preload adjuster will cope with .5mm difference though
Some dub bb’s have a spacer on the NDS depending on the size of the bb shell though?
I do have what appear to be 2x3mm metal bb spacers in the dub bb box I’ve got though. Could put a 2mm plastic crank spacer on the driveside and a 3mm bb spacer on the non drive side?
Yeah; that's what I mean - space the shell on NDS; space the crank on the DS. I'm sure as long as nothing rubs it will be fine. I'm just not sure if that's the root of the problem for you I guess 🙂
On paper you are only .5mm outboard vs my BOOST setup (comparing cassette->chainring)
boost is 7mm wider at the back so the cassette should be 3.5mm further outboard; with a 3mm offset ring vs 6mm for non-boost. (Not trying to patronise anyone; just working my logic out on paper in case it's wrong 😀 )
You’ve thought about this more technically than me!
All I know is the chain looking very wonky when in the biggest cog at the back and I think that’s causing some of the issues. I just want to check the mech hanger isn’t bent / misaligned before going mental with spacers....
I think the angle on the chain looks pretty sketchy anyway (especially from an old school do not cross the chain pov) on modern setups. I'd rule everything else out first before I went crazy with the spacers - hanger alignment; tension on mech; is it the right chain (e.g. you're not running an 11 speed chain on a 12 speed cassette)
Definitely an 11 speed chain, cassette, mech and nw 11 speed chainring.
Just hanger alignment and brake screw tension to play with before spacing differently I reckon!
I recently installed a 1x12 SRAM eagle GX with a 73mm bsa dub BB. I also have a 135 QR rear. I used the supplied 4.5mm spacer.
I initially had some shifting issues but these were resolved with some b gap adjustment. I think the SRAM system is very sensitive to chain length (therefore tension) and B gap.
Might be different with the 11 speed but I'd check the manufacturers installation advice again before going down your own random solution route with different spacers...
It’s a Sram bb, crankset, chain and chainring. Shimano mech / shifter and Sunrace 11-46 cassette.
Followed the Shimano setup as far as I can, but no amount of b screw adjustment gets the big teeth on the cassette to line up with the line on the rear mech. This is the new style deore 11 speed mech - it’s very similar to my XT 12 speed one.
I’ve sized the chain according to the exact instructions (not the typical chain plus 2 links like older mechs). I don’t think I could go much shorter looking at the mech when the chain is on the biggest cassette cog, not much longer looking at the chain in the smallest cog.
I’ve never had an issue with Sram 11 speed being sensitive particularly to chain lengths - I’m finding 12 speed shimano mechs to be a bit finicky. From what I’ve read Sram 12 speed is just as finicky.
My other bike is firmly staying with Sram 11 speed - I’ve got no desire to have anymore 12 speed / new style mech ‘fun’ in the near future!
Borrowed an alignment tool - the hanger wasn’t straight (brand new frame at that). Tweaked it using the tool and suddenly the gears are a lot better. Also put in a longer rear piece of outer cable as I thought it looked a little tight. I reckon the gears are now acceptable to hand the bike over to my nephew - but I may just do a final bit of b screw tweaking tomorrow. Chainline still looks a little uncomfortable in the biggest couple of cogs....I’m still tempted to tweak the chainline and see how that looks!
Thought I'd chime in - same issue. I have a Specialized Epic HT 2020, Power2max boost with a SRAM GX DUB crank and 36t Absolute Black chainring. Loads of clearance on the frame.
The chain line is awful on the largest cogs and I recon why I'm going through chains every 2000km
I've just replaced the bottom bracket with a Nukeproof bsa BB. 73mm shell so only using the 4.5mm spacer on the drive side.
I've just put 1mm chainring spacers to move the chainring towards the frame. Helped but not much.
Any other ideas?
Either the chainring isn't offset enough
Or that 4.5mm spacer is moving the driveside out too much. But looks centered. ??