Almost all new cars are now fitted with aluminium alloy wheels, and they are also the wheels of choice for anyone doing up or customising an older car.
What are alloy wheels?
The term alloy wheels typically refer to car or motorcycle wheels that are cast out of certain grades of aluminium alloy. They were first devised by ALCOA in 1948, and have been constructed of many different non-ferrous materials including magnesium alloys, leading to the term ‘mag-alloy wheels”.
Magnesium is rarely used now due to cost issues and the vast majority of wheels are composed of various aluminium alloy compositions, which offer the right combination of mechanical properties, durability, and cost. Alloy wheels are never left unfinished and have a substantial protective paint and lacquer layer to prevent them deteriorating too quickly.
Alloy wheels differ from steel wheels by virtue of being a different material (aluminium alloy as opposed to steel – an alloy of iron and carbon), aluminium wheels are generally more ornate than steel wheels, which usually have plastic wheel rims fitted to make them more attractive. While aluminium wheels have a tough protective paint layer. If this is damaged, then the aluminium underneath can start to corrode, further destroying the layer from underneath. If this happens, the wheel can be refurbished.
Alloy wheel repair
If your aluminium wheels have been damaged, and are starting to look tatty, they can be repaired by a professional. Damage usually occurs if the wheel has been abraded against a kerb, or struck with something sharp enough to break through the lacquer. In those cases, the damage should be rectified as quickly as possible to prevent further deterioration of the aluminium alloy under the top coating.
Alloy wheel refurb usually starts with a complete removal of the lacquer coating to expose the aluminium alloy underneath. This is usually done by immersing the entire wheel in a chemical bath, which attacks the lacquer layer and removes it while leaving the aluminium of the wheel untouched.
Once completely free of the protective lacquer coating, the alloy wheel repair technician will check the entire wheel for cracks and dents. If the wheel is cracked, or has a dent in certain areas of the rim, it may slowly leak air, leading to the tyre running flat.
Cracks generally mean that the wheel cannot be used, as they undermine the strength and integrity of the wheel. However, some dents can be repaired with a special filler that contains aluminium powder that dries to look very similar to the aluminium alloy of the wheel. It is also tough enough so that it can be filed and polished into the shape of the wheel, leaving a form that is indistinguishable from the actual metal of the wheel, once a new layer of lacquer has been applied to the whole wheel.
Once any repairable damage has been fixed, and the technician is happy that there are no cracks evident, the wheel is thoroughly washed and dried and then primed for painting. It is checked once more, then painted and the wheel baked at just under 100°C before finally being lacquered and baked again at around 110°C. It is then rechecked and, if okay, refitted to the car.
Alloy wheels in summer and winter
Many people choose not to use aluminium alloy wheels in winter as the addition of salt on the roads to deal with ice can be very destructive to the lacquer and the alloy underneath. Once the clear protective coat is damaged, the alloy can start to corrode. The corrosion causes whitish patches on the alloy wheel. Even scratch can cause alloy wheels to begin to corrode.
Alloy wheel corrosion is also caused by a reaction between the aluminium alloy and the salt, grit or other deicing substances that are used on roads in winter. If these substances sit on top of the alloy for too long, the wheel will corrode. Since the alloy wheel corrosion repair cost can be quite high, it’s best to change your wheels for winter.
Since removing and fitting tyres to aluminium alloy wheels can carry damage risk, and alloy wheel corrosion treatment can be expensive, it is often the case that a driver will have two sets of wheels for their car, one with summer tyres for the warmer months and one with winter tyres for when it is colder.
Winter tyres may have more defined tread patterns and a higher tyre weight to help deal with slush and snow. Summer tyres might also be low profile tyres to deal with cornering at speed in a better way.
Ideally, these two sets of tyres are switched in the autumn and spring to give the driver maximum control during the different seasons of the year.
Aluminium alloy wheels make your car look great, but only if you keep them in great condition, so look after your alloy wheels.