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One bit of my rim (less than the distance between 2 spokes) is 0.2--0.3mm wider than the rest. It causes a pulse of increased braking once per revolution, which is annoying. As the rim isn't worn and there are no signs of thinning, I'm inclined not to be too concerned, but I'd like a 2nd opinion - and even better if I could make it less annoying.

This is a fairly lightly used aluminium rim - I bought it new to build up a dynamo wheel for commuting a couple of years ago. That bike died, but I've put the wheel on another bike. I noticed this issue on the previous bike, but didn't solve it (I assumed it was the join).

The rim has a spot that's a tiny bit wider than the rest. I can feel the increase in the braking (V-brakes) at typical everyday braking forces. Having assumed it was the join, or a rough patch, I looked a bit more closely, cleaned and felt all round the brake track. No issues detectable by sight or touch.

Walking the bike with very light pressure on the brake allowed me to find the spot where it catches and get the Vernier calipers out. It's neither near the join or the valve hole. The wear indicator groove in the brake track is as good as new, and the brake tracks aren't shiny enough to see if a reflection is distorted on one side or the other.

Measurements with no tyre showed variation on a scale of 0.1-0.2mm inside and 0.1mm outside except this spot that was 0.3mm above the minimum, with no correlation inside to outside. In practice there was also a measuring error on a similar 0.1mm scale even taking the lowest of 3 measurements in almost the same spot (probably due to minor scratches/dings, or just to not squaring up the calipers perfectly). Without the weight of the tyre+tube, it was harder to locate the problem region by spinning the wheel and taking up the slack in the brakes, but I didn't have time to fight the tyre on, off, and on again over lunch and it needs to be rideable this afternoon. It does seem to just be variation in the extrusion.

Unfortunately the bike is now the one that never goes home, so I'm limited in what I can do to it.

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    I don't have the rim make/model details here; I may be able to find the original order
    – Chris H
    Jul 24, 2023 at 9:06
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    Does the area look deformed or irregular in any way? Does it deform (more than the rest of the rim) when inflating the tyres from 0 to maximum pressure? Is it deformed from the inside as well or does it just seem to be additional wall thickness?
    – Michael
    Jul 24, 2023 at 9:21
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    @Michael good questions I should have answered when I had it near a decent pump. I do have suitable calipers in work so will be able to test eventually. But there's nothing visible on close inspection in good light, and I couldn't feel anything either.
    – Chris H
    Jul 24, 2023 at 9:24
  • @ChrisH thought - is the bulge the same when the tyre is not inflated ? If the brake track lump decreases, it could be a literal weakness in the metal and its being deformed by air pressure. In this case, I'd write the rim off.
    – Criggie
    Jul 24, 2023 at 11:17
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    @Criggie I'm inclined to agree. No time to let the tyre down and test for a day or two, but it's been stable for some time. I noticed it on the last bike, which died in November, put the wheel away inflated (it held pretty well, not far short of rideable after 8 months), and pumped it up a week or so/50ish km ago when I fitted it to the new thing.
    – Chris H
    Jul 24, 2023 at 11:47

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Next time you get the tyre off, check the inside of the rim at that point. If the rim wall is bowed out at that point but has a consistent thickness, this will be where the rim eventually fails. Could be decades away. I suspect this is most likely.
I've tried re-bending an aluminium rim wall back inward and while it succeeded initially, I saw cracks developing so it was time to shop for a new one.

If the rim gets thicker here (ie, the inner wall is straight without deviation) then it may be feasible to thin-down the braking track and then polish the braking track.
This is unlikely though not impossible, because rims are made as an extruded coil which is then snipped and one "turn" becomes a rim. So a thicker rim wall is improbable.


If it were a thickness in the wall, like a callus, the machining process to fix that would be some combination of difficult, sketchy, and expensive. But if the rim is unuseable otherwise, what have you got to loose?

Spinning the entire assembled wheel on a lathe would need an enormous lathe that only the largest machine shops would have.

Mounting the wheel in some kind of jig that allows it to rotate under an endmill spinning in a milling machine, might work though would be janky and need a lot of weird fixturing.

Grinding it down by hand is going to be error prone, though a finger sander might be a good solution if you go slowly and can test often.

My approach considering the bike is remote, you might get away with some 120~150 grit sandpaper. Wet and dry would be best, not cheap garnet paper. Start by somehow marking where the high spot is, with sharpie or paint marker or a strap of masking tape around the two nearest spokes. Then ~5 strokes with a small piece of sandpaper right on the crest, and retest. You can do this with the tyre in place too. Just be careful to not overshoot. When its close step up to ~400 grit, and scuff the whole rim for a consistent finish to prevent surprise grabbing on the new toothier surface.

Consider that any improvement is good, and you will likely never make it perfect. Personally in the short term, I'd just live with it and be aware this bike will use brake pads a little faster than normal.

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    I'm unlikely to need to take the tyre off any time soon, so I'll have to do it specially (first deflating fully and measuring again to check for an obvious weakness. For thinning I think I'd use a combination of radial strokes by hand, and sandpaper mounted on some brake pads for tangential movement that's guaranteed to be in the right place with normal brake modulation. That would do the final finish as well, and I can invest the time at home in prepping the pads. But I agree a thicker wall is unlikely.
    – Chris H
    Jul 24, 2023 at 11:51
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    The calipers in work are easier than the ones at home (digital rather than Vernier, so better for reading on an angle and many times in quick succession), so there is some benefit to looking at it here.
    – Chris H
    Jul 24, 2023 at 11:53
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    Well, I spoke too soon. A puncture last night (on a Gator Hardshell) led to a run to the station and a need to take the tyre off today
    – Chris H
    Jul 25, 2023 at 10:27
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    @ChrisH "Serendipitous" is the word of the day.
    – Criggie
    Jul 25, 2023 at 21:00

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