I’ve bought a new bike (Trek 1.2) and the chain rubs against the front deraillieur cage because the chain rings are wonky. It happens in both chainrings, so I’m assuming it’s the crank or axle that is awry. I’ve taken it back to the shop I bought it from and the guy is saying that this lack of precision is normal and to be expected in everything other than the really top end chainsets. My question is this: Really? I have never come across this before. I have measured the chain line and it varies by about 3-4mm during one turn of the cranks and it is annoying because the change is too great to dial out using the limiting screws and cable tension etc. Is this amount of movement really to be expected?

a bit of movement is common but 3-4mm is a lot (I assume not under load as well). Did you check the other bikes in the shop at a similar price range? I’ve not got below 105 on my road bikes but I can’t believe 3-4mm is common on Sora/Sub-Sora level

It’s a Sora level bike with an FSA ‘Vero’ chainset. Yes not under load, no did not check the other bikes in the shop. Didn’t even think of that!

I think your LBS is feeding you BS. I’ve never seen 3-4mm variation in chainline during one rev. If its that wobbly now what’ll it be like in a couple of years. Vero chainset is budget but I wouldn’t expect that.

It’s less wobbly, more bent. Think I’m going to take it back for a second time.

start making noises about not fit for purpose if theyt won’t fix it.

Bendy chainrings are pretty common on cheap chainsets- normally fixed by careful tweaking with an adjustable spanner.

I’d hang off screaming “not fit for purpose!” as it’ll probably not do you any favours, but the bike shop really should sort the problem for you. It’s not like it’s difficult.

I did say noises, not a full blown tantrum, and only if he’s fobbed off again.

I’d check the chainring is bent by taking it off the cranks and laying it on a flat surface before I started tweaking it with a spanner.

Surely that’s not the point, the bike shop should be doing that!

Never disputed that the shop should be doing the straightening