Got a stiff hardtail frame with a 135mm rear end. FSA Comet chainset with 4 arm spider and straight 96bcd 30t chainring. Axle is shorter than my boost Fsa Comet chainset in my boost hardtail. 12spd HG cassette with a 1mm spacer behind it for the freehub to fit.

I’ve been reading about chainline measurements, but to me it’s easier to just say that the chainline is on the 7th gear and I think it needs to be 6th?

I haven’t messed with chainlines since using a 3pc BMX type crankset in an MTB way back, and then it was different axles and BB spacers. So, this means I need chainring spacers? What size? I can get 1/2/3/5mm spacers. Which spacers would then be so long that they then require me to also buy longer chainring bolts?

I’d rather ride this bike than buy a BMX for riding street, even though I’m sorely tempted. It runs 26 or 27.5″wheelsm I’d be tempted to go 24″ but tyres are limited where I am.

Would Imagine the spacers should be whatever it takes to move inboard a whole cog separation but you’ll have to be careful of tyre clearance as that’s why “boost”

Another alternative here (thought about it later this afternoon, it’s late now) is perhaps more spacers behind the cassette, to push it outwards?

My freehub appears to be weird. Looks like HG-C but isn’t. So, I needed a 1mm Spacer to mount the cassette with the unit rattling. I bought a few: 1mm/1.5mm/2mm.

I’ll put them all on tomorrow and see if they shift the cassette over to the chainring. It’d be somewhere between 3.5-4.5mm adjustment. I have no idea whrlat the space is between cassette sprockets, but I’m sure I could find out. A further option would be a combination of slcassette spacers and chainring spacers so I don’t end up with the chain running on the tyre

What problem are you trying to solve? For 12 speed, chainline being nearer to the biggest cog is a good thing, if tyre clearance not an issue.

It’s not that important with 12 speed imo, single ring means no big crossovers and the chains are pretty comfortable with big differences. I’d say build it then worry about it if it’s noticable

The problem is that the chainline is on gear 7 and I can’t adjust it to get the shifter working both ways, and working equally across all gears.

Also, first time I’ve used an extension link (cassette is wide range, 11-50t I think) so setting up is a pain. I kept removing chain links, one at a time, until it got so tight with the clutch on that i added one back. Still nowhere near happy with the setup.

The problem is that the chainline is on gear 7 and I can’t adjust it to get the shifter working both ways, and working equally across all gears.

Also, first time I’ve used an extension link (cassette is wide range, 11-50t I think) so setting up is a pain. I kept removing chain links, one at a time, until it got so tight with the clutch on that i added one back. Still nowhere near happy with the setup.

Have you checked (with a tool) your derailleur hanger alignment? Especially with using the extension link which will amplify any discrepancy. 12 speed has narrower gaps between gears so can be more sensitive to alignment issues.

The tighter you make the chain the more critical the chain line will be ime – I’d have shied away from going fully tight for that reason.

Frame is brand new, but I can get the tool out and check the hanger as a last resort. I am using a link on it too.

I had this situation were the last couple of gears had the chain practically laid on the top of the chainstay, so I was removing a link at a te until I went too far, and with the clutch on it almost felt seized up on the bigfmgest two sprockets.

Frame is brand new, but I can get the tool out and check the hanger as a last resort.

I check alignment on new frames and bikes as a matter of course…some have been out by quite a bit.

I’ve learned not to trust new frames (or complete bikes with a million point inspection) to have a straight hanger.

First thing I do to a bike these days is check (and usually adjust) the thing.

check the hanger as a last resort.

first resort, surely?

The extender link was the problem. It wasn’t straight when fitted. It wouldn’t stay put when bolted on. I’ve removed it and my tool shows the mech hanger is straight now.

Shifting not right yet. Have to mess with the cable again (no barrel adjuster at the rear mech) and might be okay. Hopefully it is. Using a 12spd oversize cassette on a non-boost frame without a link is going to be touch n go.

Which cassette and mech are you using? We’ve done sramano 12speed on two non boost bikes with chainlines from ~boost (outer ring of a double) to inside non-boost (spaced in from a triple) and not had any noticeable problems with chainline.

Shimano M6100 rear mech
Sugek m9012-50t cassette

The chainline is on gear 7. I’ve yet to find my cassette spacers in one of my parts boxes, and try shifting over the cassette a bit.

Can’t order chainring spacers until the covid lockdown is over (day 15 here) as the highways have checkpoints only letting registered food/medicine delivery staff through.