Uneven rim wear

[NickNick]

My front wheel which I recycled from the crappy second hand ammaco bike (it's wasn't a good bike to start with and previous owner hadn't done any maintenance, but it was free and got me into riding...) Has some pretty uneven wear. One side of the rim is pretty flat where the pads make contact but the other side is noticeably concave. I'm getting a new wheel built in new year so not too worried about it for next couple of weeks, but was wandering what could cause such uneven wear? Could it be brake setup or just bad luck? Would rather not eat through new wheel any faster than necessary if there's something I can change.

 

[raleighnut]

Sounds like the wheel has been ridden for some time with poorly set-up brakes

 

[SkipdiverJohn]

Any braking system comprising two opposed shoes actuated by freely floating pivoted arms is, by definition, self-compensating. If you are getting more wear on one side of the rim, then one of the pivots must be stiff, therefore the shoes aren't fully free to float to equalise the braking forces. The answer is proper lubrication & adjustment.

 

[NickNick]

Sounds like the wheel has been ridden for some time with poorly set-up brakes

Any braking system comprising two opposed shoes actuated by freely floating pivoted arms is, by definition, self-compensating. If you are getting more wear on one side of the rim, then one of the pivots must be stiff, therefore the shoes aren't fully free to float to equalise the braking forces. The answer is proper lubrication & adjustment.

That would make sense, the bike I've taken the wheel off used to have single pivot brakes, they were appalingly set up when I got the bike. I've only recently noticed this but from the amount of wear on that side, my guess is that the uneven wear stems from then. The current bike I've fitted the wheel to has some decent shimano duel pivots, so it shoudn't be a problem when I get my new wheel, but will keep an eye out just in case. Will have a play with the pivots when I fit the new wheel just to make sure that one of them isn't stiff.

Turn it round to even it up.

I'll have my new wheel in next couple of weeks so not too bothered about it for now, just want to make sure I don't have the same problem with the new one.




Thanks for all of the advice everyone!

 

[NickNick]

[QUOTE 5081606, member: 9609"]How thick is the wall and is it concave all the way round ?
I had one that went notably concave over about an 8" section, it had got very thin (0.9) and had bent, I could make out tiny cracks where it was failing.

View attachment 387446
what looks like a silver line is the rim cracking[/QUOTE]

I'll have to check thickness when I get back to Brum, haven't got acess to calipers down here, its concave all the way around.

 

[SkipdiverJohn]

It shouldn't really matter if brakes are centre pull or side pull with a centre pivot - IF they are free to swivel about their pivots. No matter how carefully you might try to set things up one shoe will always make contact first. Then, as the brakes are applied more, the whole mechanism will move until the second shoe is brought into contact. Only then do you get any meaningful braking. If the pivot points are stiff, it takes more force to overcome the friction in the mechanism, so the first shoe will be in heavier contact. I've come across caliper brake set-ups that were partially seized, so one brake shoe was doing most of the braking effort, and the other one was effectively a passenger.

 

[confusedcyclist]

It would take something quite special to concave one surface and not the other, unless one pad had some significant contamination, I'm thinking metal shavings, whilst the other shoe was kept relatively clean. Not sure who would do this in practice, other than a complete idiot. Therefore John's assumption is the most logical explanation for why one side might be more worn. Braking performance would be horrific in the event of a seized calliper and it's not something anyone who knows anything about basic bike maintenance would put up with for long.

If the wheelset is worth keeping, take the wheel to your LBS to be rebuilt with a new rim to save the rest from landfill. It may be more economical to buy a cheap wheelset though, particularly if the hubs have never been serviced and the cones are pitted and worn. Might be worth having a poke around inside for a service learning experience if it's as good as scrap anyway.

 

[SkipdiverJohn]

If the rims are 26", just pick up a crappy old BSO for a couple of quid and take the wheels off that. Far cheaper than buying new rims and getting wheels built. The full-sus variety seem best for parts as most of the ones I've seen have probably only ever been ridden a few times before the rider gave up on it.

 

[confusedcyclist]

Then you'll have a BSO to discard at the tip