If your rims become too worn, braking performance will be compromised, which is far from ideal. In extreme cases, the wheel may fail because there isn’t enough material in the rim wall to cope with the forces exerted upon it by the high-pressure tire.
But how do you know when your rims are worn out? We’re here to help with top tips on what to look for.
Aluminum rims
As we said, at the top, rims primarily wear out because they are used as a braking surface by caliper rim brakes. This is eliminated if you’ve got disc brakes, as the hub-mounted disc rotor is the braking surface, not the rim.
Many rims have a wear indicator. This indicator is designed to make it simple to determine when a rim is nearing the end of its life and remove any uncertainty about when to replace it.
There are two common types: a groove and a hole. Like the one in the pic above, a groove is added to the rim’s entire circumference at the center of the braking surface. Over time, this groove becomes shallower; when it disappears, it’s time to replace the rim.
The other common wear indicator is a small hole in the sidewall, like in the photo at the top of the article. You know it’s time to replace the rim when this hole disappears. Easy.
Why does a rim wear out, though?
The constant pressure of the brake block pressing against the aluminum rim slowly wears out the rim. It’s that simple. That black muck that you wash off your bike after a wet and gritty ride? That’s your aluminum rims wearing away.
“Rims may be worn during this second function as a braking surface, especially from intensive or prolonged use. Rims may experience wear for reasons as diverse as the buildup of gravel or mud in the brake pads or the use of worn or poorly adjusted brake pads. These can wear down or damage the rim sidewalls and may not be noticed by the user,” says Mavic.
How long a rim lasts depends on many factors. Mainly, it comes down to how much you ride and how often you brake, and the terrain you ride can be a factor. Live in the mountains? You’ll probably use your brakes quite a lot. Commuting in a flat city? Maybe not as much, at least not as heavily as trying to slow down from 80kph!
We asked Shimano’s Ben Hillsdon how long a rim will last. He says, “It’s difficult to say because it depends on the force of your braking and the cleanliness of your pads and rim. Suppose you can avoid excessively dragging the brakes and clean your bike regularly, paying particular attention to the braking track on the wheels and the face of the brake pad. In that case, you’ll significantly extend the life of your wheels.”
Hunt’s Ollie Gray says many variables can affect rim lifespan, including brake block compound, braking frequency, terrain, and weather conditions. “The lifespan can fall within a pretty huge window,” he explains. “In the worst cases, riders may experience rim lifespans as short as 1500 miles, perhaps up to 120,00 miles in the best cases! So, as you can see, it’s tricky to put a figure on.”
Not all rims are the same, either. Some are designed to be as light as possible, so the sidewalls are thinner to reduce weight. In contrast, rims designed for heavier-duty riding like touring and commuting will have more material in the braking surface and will last longer. Ceramic-coated rims can improve a rim’s longevity but cost a lot more than a regular rim. However, they can be a good option if you do a lot of miles.
Cleaning your rims
It’s worth paying close attention to the rims. Make it part of your regular bike wash and maintenance schedule, paying particular attention to the rims’ profile, condition, and brake blocks. You’ll want to remove any debris or grit that might be caught in the brake block, as this can damage the rim’s braking surface.
Regular cleaning of your wheel rims and brake calipers is a good recommendation, as important as cleaning the chain and derailleurs. A regular visual inspection will alert you to a worn rim or brake block. To clean the rims, you can use the same cleaner you use for the rest of the bike, something like Muc-Off or hot, soapy water, to clean the rims and brakes. You can use isopropyl alcohol or a degreaser to clean the rims more thoroughly and use one of those sponges with a scourer on the other side.
Turning your attention to the brake blocks, you’ll want to remove any debris, stones, or glass that can sometimes get embedded in the rubber. Left untouched, this debris will damage the rim and decrease braking performance. Removing the wheels makes getting a closer look at the brake blocks easier. Use a pair of tweezers and pry out any debris. Also, remove any buildup of crud in the grooves.
The brake blocks will wear out much quicker than the rims; that’s okay. They’re designed that way. You can choose different types of brake blocks to suit various conditions. Generally, a softer compound will prolong the rim life compared to a harder compound brake block.
And the compound of the brake blocks you use can make a difference, too. Hunt’s Ollie Grey tells us: “Again, there are a few variables to consider, but on a basic level: softer compound pads, which offer greater modulation and are best used during the dry/summer months, won’t deteriorate the rim’s braking surface as much as they’ll deteriorate themselves. Harder pads are better for year-round riding, but owing to their firmer compounds, will cause more wear on the braking track over time.”
Shimano recommends using a certain quality of pad to match sure brake calipers. “All Shimano rim brake clincher wheels have an aluminum braking surface, so with these, you don’t need to use a specific type of pad compound, although we recommend a certain quality of pad to match certain brake calipers. Our Tubular wheels require carbon-specific pads. Whether you use Shimano Dura-Ace, Ultegra, or 105 calipers, though, they are all compatible with the standard R55C4 or carbon-specific R55C4-A brake shoes,” explains Shimano’s Ben Hillsdon.
A brand-new rim has a flat braking surface. A highly worn side is easily identifiable by a concave shape. You can spot it by eye or use something with a straight edge, a small tool, to detect the rim’s curved shape. The reduced thickness of the side causes the rim’s concave shape; the material has been worn away with all the braking.
That reduced thickness will eventually lead to a structural failure, with the thin rim insufficient to contain the tire bead under high pressure. This either happens when you inflate the tire or w, orse w, when you’re riding. The latter is something you want to avoid.
Carbon fiber rims
That’s all for aluminum rims, but what if you’ve got carbon wheels? Generally speaking, you want to follow the same steps as aluminum rims, regularly checking for debris caught in the brake block and ensuring all surfaces are cleaned daily. Checking for rims: wea is worth checking with the maker of your carbon rims to find out what they recommend. A curved side, like with an aluminum rim, is a telltale sign of a worn carbon rim, so that’s one thing to check for.
But it’s harder to tell by eye when a carbon rim is worn out – you won’t find handy wear indicators like on an aluminum rim, so you want to pay particular attention to the carbon surface.
Generally speaking, carbon fiber rims are constructed with a layer of material laid over the brake track to give an excellent braking performance, prevent heat buildup, and prolong the rim’s life. Underneath this top layer is the raw carbon weave. If you’ve been using your carbon wheels so much that this structural layer has become exposed, it could be time to replace the rim. Sometimes, the edge can become discolored in this area, or you can see through the top carbon layer.
Hunt’s Ollie Gray backs this up by adding that you must check for visible carbon weave. “Carbon brake tracks are much more resilient than alloy braking surfaces and generally will not show the same bowing/caving as alloy surfaces. While they will curve inwards to a degree, this is not normally the telltale. What you should look for instead is when the woven fibers of the carbon itself begin to become exposed or frayed,” he says.
“If you run your hands or /fingers across the braking surface and it feels rough or fibrous, that’s normally a sign the resin has worn away. As stated above, however, this resin on carbon braking tracks is quite resilient, and of course, carbon brake pads are of a softer compound, contributing to the increased lifespan. To date, we’ve not known of any of our carbon wheelsets out on the road to have completed a lifespan.”
You might also notice a judder during braking that didn’t occur when the carbon wheels were brand new. This could be a sign of the brake track wearing out, and it is an excellent time to inspect the rims professionally.
Each carbon rim brand recommends a specific brake block, and it’s strongly recommended to stick with this recommendation, as using another carbon-specific brake block could harm the rims.
“You must use the proper brake pads for your specific rims. Using improper or contaminated brake pads will lead to excessively high braking temperatures, which can cause premature rim wear and failure, leading to serious injury and death,” warns Zipp.
Now that you know how to spot a worn-out rim, what are your choices for replacing the worn side? In most cases, you can return to the edge, and all good bike shops will happily do the work for you. Building a wheel isn’t as scary as you might imagine if you fancy doing the job yourself, and there are lots of good wheel-building guides available online if you want to go down that route.
