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I have v-brakes which have started to groove my rims. What is the surest way to know if they need replacing?

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2 Answers 2

Most rims have a little dimple or a groove (called wear indicators) for detecting rim wear. When this dimple or groove disappears, its time to get new rims. If the wheel physically damaged, take it to a LBS for an assessment on if it needs to be replaced or can be repaired anyway (e.g. cracks, dents, etc.).

If your rim doesn't have wear indicators, take it to a bike shop, and they'll measure the rim widths with a caliper and check for deformations. I don't have a good threshold for what thickness would be considered acceptable, but I'd err on the side of caution.

If your v-brake is grooving your rims, are you sure brake pads are still good? If you hit the metal back plate, they'll start destroying rims. If the groove is on the brake pads (due to the wear indicator or misalignment), you can sand it down if theres still enough material left, or just put on new pads.

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On some rims such Mavic Open Pro the rim is drilled part way through from the inside - so for these rims you need to look for the hole appearing rather than something wearing away. –  Jackson Jan 20 at 13:12
    
Good point. This is probably the easiest way to gauge rim wear. –  Batman Jan 20 at 21:56
    
Some brake pads tend to attract little metal splinters or similar, scratching or grooving the rim afterwards. A wire brush is very good to brush these out of the pads. –  arne Jan 21 at 9:35
    
The dimple or groove that indicates rim wear can actually reduce the lifespan of the rim. I talked about this with my bike shop the last time they replaced my wheel. They brought out a wheel that they had just replaced, which had failed along that groove. Clever idea, though. –  Precipitous May 8 at 16:48

If your rims bulge outwards under a high pressure inflation, its probably a sign they're sufficiently worn to require replacement. This can be detected by sporadic rim brake effectiveness when brakes are correctly set, as in, rubbing during one point of the rotation, or variable braking capacity during a spin of the wheel. It feels like shuddering.

In terms of the pressure required to detect:

on 47-559 which given my weight & use I run at 33psi / 53psi

Rim bulge was detectable at 60psi and obvious at 80 or 100psi.

Source = Failure mode of my most recent rim.

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A blip isn't really a good indication of a failing rim - often, these rims can be put into (near) perfect working condition by a bike mechanic (or yourself) with a crescent wrench and a bit of truing (certainly, if you carry a small crescent wrench, you can often do this as an on road repair then adjust it when you get home). –  Batman Jan 20 at 7:01
    
I went through alignment a bunch of times before watching the distortion when I pumped it up. –  Samuel Russell Jan 20 at 8:29
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What is high pressure inflation? For some bikes, high pressure is 4 bar / 60 psi –  Vorac Sep 10 at 13:31

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