Will 3mm make much difference to a chain line?

Might be getting a boost 141 qr rear frame. I have a 135 qr wheel. Trying to do this as cheaply as possible, I reckon I can replace the axle and space the nuts further out by 3mm per side, and space the 6-bolt disc out similarly. But that will mean the cassette is effectively 3mm too central.

Will that make much difference to my shifting due to altering the chain line?

What hub?

I don’t remember ever seeing a boost kit for qr. By axle do you mean the QR skewer or actual axle in the hub. I’d not recommend just replacing the QR with a longer one and spacing as this will put the load onto the QR which it is not designed to take. 142->148 kits work because the 12mm axle is taking the load. If you mean replacing the actual hub axle then why not add all the spacers to the disc side and re-dish the rim. The cassette would be in the correct place then.

Chainline is a compromise wherever you put it – different recommended ones are just optimised for a particular area of the cassette to minimise the effect. Doing the above, you may find it works fine or it may be slightly worse towards the ends of the cassette.

Your other alternative (which most of the kits do) is a 6mm axle spacer on the non-drive side (with disc spacer) and re-dish your wheel to bring it back to the centre of the frame – that way the cassette stays in the same place relative to the derailleur.

Thanks.

Yes my intention was to replace the axle itself from 135 with a 141mm one.

I was hoping to avoid a re-dish but I guess that makes the most sense in the end. Could always try with the easy 3mm per side approach and if it isn’t working move to 6mm on the non-drive side

A redish will be simple and quick enough and solve your issue. I’ve done this for exactly this reason and it was fine.

If you’re after an X Caliber frame, send me a PM. I have a few for sale and, if we have one knocking about, you can have a back wheel with it for nowt.

Personally, in mine, I use a non-boost 142mm axle wheel with QR end caps in. The chainline is atrocious but it works so I don’t care.