KC8QVO

Here is a close up shot of my rear rim. The bike has 270 miles on it, most of it lightly loaded. The brake contact region on the rim is noticeably worn. The front rim isn't nearly as noticeable - I suppose I use the rear brake to a much higher amount.

The bike is a Dahon Mariner D8 at 270 miles.

Does anyone else have any observations from their experience to compare? I expect rim wear. That was a consideration when I got the bike as I was aware of higher mileage riders burning through rims with rim brakes seemingly quite easy on the smaller wheel bikes. I am still not overly concerned at the moment - its just an observation.

Does anyone have a recommendation for % wear being a "stopping point" = IE time to replace the rim before riding much more? I can mic the thickness and see where it is and keep track of it over time.

tomtomtom123

We can't tell how much wear there is just by seeing your photo. All we can see is dirt. If you want to get a clearer idea of the wear, you can take off the tire and put a straight edge against the rim and look to see now much of a concave curve is on the brake surface. I don't think there would be much wear after only 270 miles. You're probably just seeing dirt. If you want to extend the life of the rim then you should clean the brake surface of the rim and the pads every week. I have removable pads that I scrape with a knife until most of the dirt is gone.

The rear rim gets dirty faster and wears out sooner. They get dirty when riding on wet ground so I can them immediately after riding in the rain.

KC8QVO

That isn't just a line on the picture - what I am noting with the arrow and the red line zone is that is actual metal wear that is worn in to the rim's surface. I haven't pulled the wheel, but I can and measure it.

CliffordK

That black line looks like a rim wear indicator. When it disappears, your rim is toast.

I'd check your pads for sand, aluminum, and debris.

I can't say what the best pads to limit wear would be. Once you've broken through the outer smooth surface, it may be hard to recover, but keep the pads clean.

KC8QVO

I was thinking the same and was going to ask about that... Good deal.

I pulled the wheels this evening. In fact, the tire wear is quite unbalanced front to rear also so while I had the wheels off I swapped the tires around also.

The rim is actually tapered. The area near the bead is wider than the crown. The sides slope. That correlates with the wear pattern I showed in the picture earlier - the most wear is on the pad track nearest the bead.

The rim width is as follows (precision down to 1 ten-thousanth, or .0001")
At bead: 1.0085"
In wear track: .9880"

So that is .0205", or 20.5 thousandths combined both sides, or roughly 10.25 thousandths per side.

The taper in the rim sides plays in to that, also, so some of it isn't the wear - it is the geometry of the rim.

CliffordK

Your pads should wear into the rim. Or, when you install new pads, make sure they sit flat on the rim. Any taper shouldn't matter. In the past we didn't have machined sidewalls.

BMX rims should be somewhat tougher than other rims, although I am surprised to hear of rapid wear. Perhaps it depends on what exact alloy is used.

The side view in the last photo looks clean. Is that the front?

KC8QVO

The picture with the micrometer and tire off is the rear rim - same one I put the red marks on in the 1st post.

OK on the BMX rims. Back in the day I did a lot of freestyle riding. One of the coveted upgrades was a set of Alex triple wall rims. That would be an interesting addition to a folding bike. Triple wall rims would be overkill, strength-wise, for a folding bike. I'd be curious what side wall thicknesses/materials are out there at some point, though.

tomtomtom123

You're going to find that some sidewalls of the rim are variable thickness, so you're not going to be able to tell how much wear is on there just by measuring thickness. In my opinion, the way to estimate wear is to put a straight edge against the sidewall and look at how deep the concave curve of the gap is between the straight edge and the wall.

There were some manufacturers with uniform wall thickness rims that wrote on their website not to let the walls become less than 1.1 or 1.2mm thickness, but I would guess it depends on what material the rim was made out of. When I was searching for new rims, I got some there were just 1.4mm thick and returned them right away. I ended up with Kinlin rims, but it varied from 1.4mm at the top to 1.8mm at the bottom. I'm not sure how well that 1.4mm will last. They didn't have wear markers.

On my old rims with uniform thickness, the right side wear line was completely gone while the left side was still half there. I didn't figure out why there was such a huge uneven wear. There was still 1.4mm of wall thickness remaining. I'm not sure if the wear line would cause the area around the line to wear down quicker than other areas of the wall. Perhaps the wear dots would be better in this respect. Ryde has an internal wear line that you will only see once the surface is worn away and broken.

sweeks

Two suggestions:
1) Use the front brake more; it's more effective than the rear and will allow you to use the rear brake a bit less, extending the rim life.
2) Watch your wear indicator line, and be alert for "thumping" when the rear brake is applied. This is an early warning of rim failure. I've experienced this several times on my folding bike with 20" wheels. Always on the rear wheel. I haven't had an actual rim separation, but once the thumping begins I have limited rear brake application and replaced the rim as soon as reasonably possible. In a pinch, I'd lower the tire pressure as an emergency measure, but I haven't actually done this.

Lateral view of 20" rear rim crack



Radial view of 20" rear rim crack



Rim wear warning sticker

EDIT: The best way to measure rim brake track thickness is with a "dental crown thickness" gauge such as this one: https://www.net32.com/ec/besqual-iwa...unded-d-148616
These can be found for extremely low prices, but the quality varies widely. The important feature is the measuring jaws: they should be round-ended and meet exactly when the gauge reads "0". A good one is accurate to 0.1mm and can be estimated to 0.05mm. A single sheet of paper should be detectable.

KC8QVO

Excellent post. Thanks!