Any ideas what's up with my bike?

Yttroxy · 11-03-2025 11:16PM #1

The gears shift mostly fine (occasionally have to trim but not often), but when I'm in gear and a lot of force is applied to the pedal (accelerating or going up hill) it feels like the chain's skipping or something. I hear a clunk and feel the pedal slip in a similar way to how I do when changing gears, this'll happen every 10s or so until I either am not on a hill or am not accelerating any more.

The bike's a mountain bike with shimano gears with 2 front gears and 7 at the back.

It's difficult to diagnose as it won't happen on a stand or anything as it only happens when there's a lot of force through the pedals. I tried messing about with the indexing adjuster beside the handlebar grip but it doesn't seem to help, and I think the limit screws are fine (it also happens in all gears not just the highest/lowest), I'm just not really sure what's wrong with it. All components look fine, the chain's fairly new, the cassette looks fine, none of the teeth look worn or anything to me, and everything looks aligned.

cletus · 12-03-2025 05:37AM

Most obvious thing to me would be a worn chain. Do you have a chain checker?

billyhead · 12-03-2025 05:42AM

Agree with previous poster.Most likely the chain or the cassette or both. Probably best to replace both

07Lapierre · 12-03-2025 08:08AM

could be worn chain, worn cassette, worn chainring or all 3. How old is your bike? When was the last time you replaced the chain or cassette?

magicbastarder · 12-03-2025 08:34AM

if you're near a decathlon or a halfords you should be able to pick up a chain wear checker for under a tenner.

ARX · 12-03-2025 09:33AM

Even if the chain was replaced relatively recently, it may be skipping if a previous chain was very worn, which may have caused wear to the cassette or chainrings. I saw a bike the other day that had been "serviced" by a bike shop - the chain was new but the chainrings were very worn and the jockey wheel teeth were pin-sharp. The chain was skipping and the whole drivetrain looked like somebody applied used engine oil with a large paintbrush.

gmacww · 12-03-2025 09:40AM

https://www.boards.ie/discussion/comment/123256671#Comment_123256671

Plenty of life still left in that jockey wheel. I once wore one perfectly round on a commuter bike :)

Yttroxy · 12-03-2025 10:55AM

https://www.boards.ie/discussion/comment/123256452#Comment_123256452

The bike's about 5 years old, but it was in a garage barely used until about a year ago. I replaced the chain then and have been doing a fair bit of mileage on it since. I'm going to get a chain checker, and if that looks good I'll probably look at replacing the cassette.

CramCycle · 12-03-2025 11:38AM

https://www.boards.ie/discussion/comment/123256959#Comment_123256959

Take a picture of the cassete and chainring, easy to diagnose visually if worn, and you will also know for again

Johnny Jukebox · 12-03-2025 02:13PM

https://www.boards.ie/discussion/comment/123256959#Comment_123256959

You'll rarely, if ever, get away with replacing the chain without replacing the cassette.

Yttroxy · 12-03-2025 02:48PM

https://www.boards.ie/discussion/comment/123257096#Comment_123257096

There's some pics of the chainring and cassette

billyhead · 12-03-2025 02:58PM

https://www.boards.ie/discussion/comment/123257833#Comment_123257833

Looks like both the cassette and chain need replacing.

T-Maxx · 12-03-2025 03:00PM

https://www.boards.ie/discussion/comment/123257675#Comment_123257675

Sorry but this is simply not true.

T-Maxx · 12-03-2025 03:02PM

Chainring, cassette and chain need replacing.

magicbastarder · 12-03-2025 03:17PM

you can see from these teeth that they're kinda swept forward - which shows the rear of the peak has worn. so definitely cassette needs replacing, and you wouldn't replace the cassette and not also the chain.

gmacww · 12-03-2025 03:58PM

https://www.boards.ie/discussion/comment/123257675#Comment_123257675

Only if you're very lax with chain wear. Keep on top of your chain and change it on time and your cassette can last thousands of km's and many chains.

Wishbone Ash · 13-03-2025 08:52AM

https://www.boards.ie/discussion/comment/123257675#Comment_123257675

I don't agree. I change chain every 5,000kms and cassette every 10,000kms. I've been doing that for years without issue.

Johnny Jukebox · 13-03-2025 09:43AM

https://www.boards.ie/discussion/comment/123259988#Comment_123259988

Fair, that's good preventative maintenance. But if you're at the point where the chain is skipping, I don't think a chain only replacement is going to work, at least not in my experience.

tomasrojo · 17-03-2025 04:48PM

I just use a snipped-out twelve inches of an old tape measure to gauge chain wear. The distance between the centre of one pin and the pin two over is exactly one inch, so if over a distance of twelve inches the centre of the pin doesn't line up with the twelve-inch mark, the chain is starting to elongate. Sheldon Brown summed it up:

If the link pin is less than 1/16" past the mark, all is well.
If the link pin is 1/16" past the mark, you should replace the chain, but the sprockets are probably undamaged.
If the link pin is 1/8" past the mark, you have left it too long, and the sprockets (at least the favorite ones) will be too badly worn. If you replace a chain at the 1/8" point, without replacing the sprockets, it may run OK and not skip, but the worn sprockets will cause the new chain to wear much faster than it should, until it catches up with the wear state of the sprockets.
If the link pin is past the 1/8" mark, a new chain will almost certainly skip on the worn sprockets, especially the smaller ones.

https://sheldonbrown.com/chain-wear.html

Might be some use to someone who doesn't have time to wait to get a chain wear tool.

tomasrojo · 17-03-2025 04:56PM

I go for years and years changing chains (pretty preemptively) without changing chain rings or sprockets. I did change a middle chain ring on the tourer after 15 years, and the bakfiets recently had to have the sprocket on the internal gear hub replaced when I dropped in the wheel for an annual service, but that was because of damage to where it interfaced with the driver rather than chain wear.

CramCycle · 17-03-2025 07:26PM

I get multiple chains per cassette and chainrings.

gn3dr · 17-03-2025 09:00PM

Same here. Don't remember when I last had to change a cassette or chainring. However on my winter bike last week the Park Tools chain tool fitted in at the 0.75% setting so I bought a new chain. Fecking this is now slipping on a few cogs (15 & 16 tooth which I tend to use most). So must get a new cassette for that, which got me thinking do I really want to buy new 10 speed stuff and of course started looking at upgrades. 🙄. Must resist, it's only the winter bike.

Any ideas what's up with my bike?

Answers