My commuter (CX bike running 11 speed shimano 105) has recently started spontaneously changing gear when I get out of the saddle and give it some beans. I say changing gear, it's more just that the pedals lurch forward a bit and there's a crunching sound from somewhere in the drivechain.
Have tried putting on a new chain, then put a new cassette on it but to no avail. The freehub should be fine as the wheels are less than a year old and are solid handbuilt jobs. Indexing seems fine in the workstand and fine when riding too, unless out of the saddle when this issue arrises. I think it only happens in the big ring although I'm not sure I've done a hard out of the saddle burst on the inner ring.
Anything other obvious explanations other than the chainrings being worn? They don't look too bad to me, although of a few of the teeth do look a bit spiky. Probably have ~14000 km on them which isn't much at all, but being a commuter there will have been times where it was in a bit of a state for a few weeks at a time.
Cheers.
PS anyone seen any deals for 4 arm 11spd shimano chainrings?
Definitely new chainring time..
You've had your money's worth there
Anything other obvious explanations other than the chainrings being worn? They don’t look too bad to me, although of a few of the teeth do look a bit spiky.
I had the exact same thing a few years ago on my road bike, it was the big ring being worn (but didn't look it). So I'd put good money on you needing a new chainring.
At the time it was most-economical to buy a new Ultegra chainset and sell the old arms and rings. Someone even paid me £10 on eBay for the shagged big ring (sold as such).
14,000kms sounds quite a lot out of allo chainrings - especially if they’re on a commuter bike ridden in all weathers and probably a little big neglected at times in terms of cleaning / relubing etc.
I’ve generally found with 2x or 3x chainrings it’s cheaper to buy new cranks complete with chainrings than it is to buy seperate chainrings. Which is ludicrous, but there we are.
Thanks for advice.
Bikeparts.co.uk has 105 R7000 front rings for £63, and I got a 52T R5800 series for £35 (if it is indeed in stock). Inner rings about £20, so quite a bit less than a new crankset.
I was reading the OP text thinking to myself "don't discount the freehub as a possible cause". Then I opened the pic of the chainring. That, is an ex ring!
If it’s for commuting then get yourself a steel one (if you can) so it lasts forevever (well maybe not forever)
Yea, I've been chasing a slipping chain on my road bike. It only seemed to manifest itself on zwift and the new turbo trainer, whenever the power crept over 500-600W it would skip.
New chain, new cassette, new mech hanger, and finally new chainring before I solved it.
Weirdly, had zero problems outdoors. Even though I'm sure I can put down significantly more torque from a standstill than the wheel-on turbo's flywheel/magnets will provide. And the chainring doesn't even look as worn as yours.
quite a bit less than a new crankset.
But what could you sell the old one for?
The chainset with the ratio I wanted was £150. I paid £53 for new rings.
Can't imagine I'd get more than £50 for a worn out chainset without being dishonest about the state of the teeth.