Nearly every new car on sale in the UK can be optioned with larger alloy wheels than the standard size, for an additional cost. Mostly it’s a cosmetic choice, but larger wheels can also alter how a car drives.
Whether you’re running through the options list when ordering a new car or buying a set of aftermarket wheels, increasing a car’s alloy wheel size has both positives and negatives. Here’s what you need to know.
What exactly is an alloy wheel?
An ‘alloy’ refers to the chemical composition of a metal. An ‘alloy wheel’ is usually a composite of aluminium or magnesium with other metallic elements, as opposed to a traditional steel wheel (ironically, steel is also an alloy but we’ll ignore that here).
Most ‘alloy wheels’ today are primarily made of aluminium mixed with other metals, which makes them both lighter and stronger than steel wheels. This, in turn, can improve handling and fuel consumption. A lighter wheel will change direction more easily when turning, so the steering feels sharper and more responsive.
The reduced weight helps a car to use a bit less fuel, while also making the job of the car’s suspension much easier as there’s less weight bouncing around at each corner of the car.
Alloy wheels have almost universally replaced steel wheels on new cars today. Only some budget models still run steel wheels, often with a plastic cover over the bare wheel. Since alloy wheels are much stronger, they can be styled with any number of spokes for cosmetic reasons, and polished or painted rather than hidden under a cover.
Alloy wheels are often larger
Alloy wheels are inherently lighter than steel wheels, so you can make the wheels larger without increasing weight too much. Car manufacturers usually offer different wheel sizes and styles (usually at extra cost) to give customers more personalisation choices when choosing the specs for their new car.
For example, the entry-level BMW 3 Series saloon is currently equipped in the UK with 17-inch alloy wheels as standard. But you can also choose from two different 18-inch designs or a lightweight 19-inch option.
Alloy wheel size is measured in inches and refers to the wheel’s diameter. If you’re buying aftermarket alloy wheels, you can also specify different wheel widths, which allows the fitting of wider tyres.
Are bigger wheels better?
This depends on your driving preferences. Generally speaking, you can’t alter the overall height of the combined wheel and tyre package on a car, because they still need to fit inside the car’s wheel arches and because the rolling height of the combined wheel and tyre is used by the car to calculate speed and distance.
So if you want larger-diameter wheels, you need different tyres to maintain the same overall height. The image below illustrates what this looks like – a larger wheel requires a tyre with a thinner sidewall (usually called low-profile tyres).
The combination of a larger wheel and a thinner sidewall on the tyre affects how a car rides and handles. The tyre sidewall acts like a shock absorber for every bump, pothole or speed hump the car hits, a bit like the sole of your shoes. If you reduce the height of the sidewall, you reduce the amount of absorption that the tyre can provide – like wearing thinner-soles shoes compared to thicker-soled shoes.
Conversely, a wheel made from alloy is very strong and rigid, with less flex than a steel wheel, so the effect of a larger wheel and reduced tyre sidewall means you feel a lot more bumping coming through to the cabin.
A smaller alloy wheel has taller tyre sidewalls (high-profile tyres), which better absorb the blows of potholes and other road imperfections, delivering a more comfortable ride.
When it comes to handling, however, larger alloy wheels with low-profile tyres generally offer better cornering grip. With a larger and stiffer wheel, combined with a thinner sidewall, the rubber tyre has less flex to move around so it stays in contact with the road better. That means the car can grip the tarmac better at higher speeds, which makes it feel more stable through corners.
In addition to simple wheel diameter and width, there are various other measurements that any replacement wheels need to match. For example, the spacing of the wheel nuts varies from car to car, while there’s also something called offset, which determines how much of the wheel sticks out from the car. That means you can’t just throw any set of wheels on any car – they have to meet a number of very specific measurements.
Tyres also have a complicated set of measurements that have to all be correct to be fitted to a specific car. We have a separate feature on those numbers to help you understand those.
Do larger alloy wheels improve performance?
The size of a wheel is only one factor in improving a car’s handling or ride characteristics. There’s also the material composition of the wheel (certain alloy compositions offer more strength but potentially also more weight), the style of the wheel (thin spokes weigh less but lack rigidity compared to thicker spokes or more spokes).
It’s worth bearing in mind that larger wheels can also be more prone to cracking from impacts on potholes, kerbs or speed bumps. Because there is less impact absorption from the tyre, more shock is transmitted through to the wheel which makes it more likely to crack.
For more advice on tyre types and fitting aftermarket alloy wheels, as well as some great deals, visit our partners below.
Learn about tyre types and browse a wide array of tyre brands with Tyre Shopper. Find out more
Find a great deal for your next set of alloy wheels and tyres with Tyres.Net. Find out more
Shop cheap tyres and brakes tailored to your car with Tyre Pros. Find out more
Read more:
