Rims

Rims

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Knowledge Level: Beginner

Rims are an essential component of the bike that are often neglected. Especially in bad weather, taking care of your wheel rims becomes even more important due to the dirt and debris that can become embedded in them. This article provides tips on how to minimise wear and take care of your rims.

What is a rim?

The rim forms the external circumference of a bike wheel and is connected to the hub by a number of spokes. These spokes pull on the rim towards the hub and this action gives the wheel its structural strength. There are two types of rim and these are defined by how a tyre is mounted on them.

The first is a clincher rim where the beads of the tyre hooks onto the rim. The internal spoke holes are covered by a fabric of plastic rim strip which protects the inner tube or, in the case of tubeless setups, provides an air tight seal. Because of the high pressure exerted by the inner tube, or the air inside a tubeless tyre, the sidewalls of a clincher rim have to be strong typically making clincher rims heavier.

The second type is a tubular rim where a sewn up tyre known as a tubular or tub is glued to the rim. As the rim does not have to withstand high internal pressures on its sidewalls, tubular rims can be made lighter. The rim, apart from on bikes with disc brakes or brake free track bikes, also provides the braking surface that the brakes pads press against when you pull your brake levers to slow down and stop your bike.

Rim materials, shape and depth

Until fairly recently most rims were made of alloy and had a simple box section shape. However, with the advent of carbon fibre and a greater understanding of aerodynamics, deeper profiled rims made entirely of this super strong but lightweight material have become increasingly common. Rim depths over 10 cm are now available and, on time trial and track bikes, spokes are sometimes completely absent with a completely solid and extremely aerodynamic disc wheel.

The main downside of carbon fibre rims is that braking performance, especially in the wet, compared to alloy rims, can be unpredictable and, on long descents, they are prone to overheating. Modern brake pad technology is resolving these issues but you will often find carbon rims with alloy braking tracks fitted as a compromise solution. Carbon rims also tend to be more expensive than alloy and, typically with fewer spokes, are more difficult to true if damaged. For this reason, many cyclists will ride the majority of their miles on alloy rims and save their lightweight, aero and expensive carbon ones for race day.

Caring for your rims

The most important aspect of rim care is to ensure that your brakes are setup correctly. If they’re rubbing on the rim, this will not only make cycling harder but will also cause unnecessary wear. If you’re unable to stop your brakes rubbing, there may be a slight buckle in your rim and you should take it to your local bike shop to be trued. You also need to make sure you’re using the correct pads for your rims. Using the wrong ones can dangerously effect braking performance or cause excessive wear. This is particularly important if you’re swapping between alloy and carbon rims.

Although there are pad compounds that are suitable for both types of rim, you should still change the pads whenever you swap your wheels. The reason for this is that tiny shards of alloy can become embedded in the pads and these can cause irreparable damage to carbon rims.

It’s important to remember that rims, which are braking surfaces, are a sacrificial component that will wear out and have to be replaced. As the sidewalls wear down with braking, they become thinner and eventually will fail. Most alloy rims will have a wear indicator on them. This is often grooves across the rim or spherical dimples that, when they disappear, show that the rim has worn dangerously thin and needs to be replaced.

Carbon fibre rims have a layer of scrim, a woven material, on the brake surface of the rim. Under the scrim layer, the carbon fibres are straight and parallel. If you can see straight fibres showing through the scrim layer, the rim needs replacing. Fortunately your rims should last you thousands of miles but you should constantly monitor wear and take a number of steps to minimise wear.

Learn to brake correctly and, on long descents, don’t constantly drag your brakes. Many riders do this without realising it so, if you think this may apply to you, get into the habit of fully extending and pointing your braking fingers.

Don’t neglect your rims during your post-ride bike wash. Wipe them down to remove any debris and use this as an opportunity to inspect for wear.

If a ride has been especially muddy or if surfaces have been gritty, remove the wheels and inspect the braking surface of the pads. Wipe them clean, avoiding contamination with any detergents and remove any embedded debris including visible alloy splinters.

Check pads regularly for wear and replace when necessary. Pads will have a number of vertical grooves on them that, once they’ve disappeared, indicate the pad is worn.

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