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Engaging the rear brake results in a burning smell and significant brake wear, so bad that within just a hundred miles or so I caused significant loss of material on a brand new pad set. Looking at the brakes after use, I find flakes of brake pad rubber stuck to/falling off of what remains, and the brake has considerably eroded.

The rim is steel. It has a gash/scratch in it that is rough. The rim also has a small dent. Interesting is that both rim pads wore down extremely quickly despite the gash/dent being only on one side of the rim. I don't think the brake is rubbing while riding, because I don't feel excess resistance, and I don't smell the burning when normally riding, only under "heavy" braking (going down a hill for a block or so). However, I did notice that one brake lever can occasionally be slow to retract; but again, extreme wear is on both pads.

I took the wheel into a shop without mentioning this issue, just asking the mechanic if he thought it was safe to ride; he said it would be fine.

The damage

Thoughts?

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    Photos of the rim, the brake pads' wear surface, and the brake setup would be very helpful. Also, what kind of brand new pads are they? Brake pads vary considerably in their quality and wear properties.
    – Armand
    Oct 19, 2021 at 3:39
  • To check for pad rub simply lift up the bike and check if the wheels spin freely. I’d sand down the gash in the rim. If the brake struggles to retract you might have to increase spring tension or replace your cables+cable housing.
    – Michael
    Oct 19, 2021 at 6:00
  • How much braking do you have to do to get the burning smell? A long descent with the need to brake to maintain control wouldn't surprise me, a single stop would be remarkable, and stop-start urban riding plausible but unlikely in most climates
    – Chris H
    Oct 19, 2021 at 7:56
  • @ChrisH I installed new pads and, with the bike upside down, applied brake pressure, and smelled that same burning rubber smell, so I can only assume not very much braking generates the smell. When I was testing it on the old pads, I would go down a moderately steep hill ~ 1 block long and use mainly rear brakes, and that gave a very strong burning rubber smell and considerable wear.
    – Avocado Surprise
    Oct 19, 2021 at 13:37
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    I'm not saying they don't exist, but I've never seen a black steel rim so I wonder of it's been painted and the paint is the problem. On the other hand that gouge in steel would take some doing, but in (black-anodised) aluminium would be easy
    – Chris H
    Oct 19, 2021 at 13:38

3 Answers 3

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I have seen various steel-rimmed bikes experience rapid pad wear in use. I only have speculative answers, but two things that are definitely true is that most steel rim bikes come with very basic components, including brakes/pads, and also steel is harder than aluminum.

The surface irregularities will only ever hurt pad lifespan. It may be possible to mitigate them somewhat, i.e. by sanding down any rough parts of the gouge.

Probably the closest thing to a good solution is get Kool Stop Salmon compound pads, which work better on steel rims than most. While not the same thing, there are other red "extreme conditions" type pads that are extra hard and may also improve things. Ultimately riders with any kind of braking needs to speak of will be much better off on aluminum rims, but it's not always practical.

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  • When I had steel rims I used Kool-Stop Eagle 2 dual compound, because I could get them more easily than the all-pink ones. They were far better than cheap Shimano, especially in the wet. But I'm not sure you want a hard compound on steel (strictly speaking, chrome, though I believe stainless rims were tried)
    – Chris H
    Oct 19, 2021 at 7:55
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It's clear from the refrigerator magnet test you have steel rims.
However, in the picture the rim looks very black. The scratch looks like it goes to the metal. So, your rim is coated with something that is probably generating the burning smell. Your old brake pads "painted" a layer of rubber/plastic on your rim.

  1. Clean the black stuff off your rims. I'd try some steel wool and a lot of rubbing. EDIT: The black stuff is paint, but there might be brake pad residue also. Steel wool will remove paint. If there is brake residue that won't come off using cleaners steel wool might be needed.
  2. The new pad set that left a coating of rubber on your rim needs to be replaced with pads that are made of better stuff. Any well known brand name pad should work. Shimano, Kool Stop, Tektro, SRAM etc.

In the comments Avocado Surprise indicates that there are already new pads on the bike. The smell will continue until the rim is clean and then you'll be able to see if the new pads have the same problem or not.

EDIT: If you have another bike you can test your brake pads on you could find out if it's the pads or the wheel that smell.

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  • The rims were sold to me black from a bike shop. So I don't think the black color is from the old pads.
    – Avocado Surprise
    Oct 19, 2021 at 19:46
  • @AvocadoSurprise Are the rims black all over? Even if they are painted black - is there rubber residue on the braking surface?
    – David D
    Oct 19, 2021 at 20:02
  • They are painted black all over, including spokes. Citrasolv rag until more clean followed by water to wipe and dried with third rag. Repeated brake test. Now it's a burnt oranges smell (this is a joke, it's still the same smell). I can try the steel wool technique later tonight perhaps, but I have a feeling then the paint will come off with it.
    – Avocado Surprise
    Oct 19, 2021 at 20:09
  • @AvocadoSurprise You are correct - steel wool will take off the paint. If you are sure there is no brake pad residue steel wool is not needed, this would mean that your current pads are burning.
    – David D
    Oct 19, 2021 at 20:39
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    @AvocadoSurprise Do your brake pads rub on the tire?
    – David D
    Oct 20, 2021 at 13:15
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I replaced the old painted, steel wheel with a new aluminum wheel and the smell is gone.

Since the old steel wheel was perfectly clean, and since I used the same brake pad set on both the steel wheel and the new aluminum wheel, and since no other issues like tire rub are the reason, I think it must have been something to do with the black paint on the rim.

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