The size of your vehicle’s wheels and tyres can greatly impact how it handles and performs, making it extremely important to ensure that you have the correct ones fitted to your car.
While the common explanation that bigger wheels provide more grip is ostensibly true, the reality is far more nuanced, and in certain situations, it may be better to prioritise smaller wheels depending on the type of driving you intend to do.
How wheel size affects your car
Larger wheel rims are often touted as a visual selling point, especially ones with an ornate design, but technical aspects should always take precedence over appearances, according to Pirelli.
The size of the wheels can seriously affect engine performance and fuel efficiency, and this applies to regular vehicles that travel on the roads every day just as much as it does to supercars.
When shopping for wheels and tyres, it’s important to understand how they are labelled.
For example, you may find a tyre with a rating of 185/55 R15. The first number in this chain refers to the width of the tyre measured in millimetres, which in this case is 185mm.
The second number refers to the height of the tyre sidewall in relation to the width of the tyre, which is expressed as a percentage; in this example, the 55 means that the tyre’s height is 55% of its width.
The R, meanwhile, stands for the radial construction, or radius, of the wheel rim, while the accompanying number denotes its size and is expressed in inches.
This means that, in our example, the R15 stands for 15-inch rims.
Certain tyres may also be labelled as “P”, “LT”, or “ST” which stands for passenger vehicle, light commercial vehicle, and special trailers.
Carmakers work closely with tyre manufacturers to determine what size wheels should be given to a particular model, which can influence the vehicle’s transmission ratio and vice versa.
Wheels with a larger diametre will reduce the transmission ratio, which has the consequence of lowering acceleration potential but improving top speed. These changes are directly proportional to the variation of the wheel size, said Pirelli.
Another consequence of increasing size is that it will increase weight on the axle, which can hamper acceleration further while also lowering cornering accuracy.
It may raise the chassis and ride height, too, which can affect the centre of gravity leading to increased rolling and oscillations.
For the average motorist, it’s recommended to stick to the wheel size the car had when it was new, as fitting smaller or larger sizes can mess with the speedometer and even cause damage over time to the stability control and anti-lock braking system (ABS).
An improperly-sized sidewall height can also damage the suspension, and the tyres themselves may wear out faster.
Matching large-diameter wheels with low-profile tyres, on the other hand, will create a stiffer sidewall that is at greater risk of a blowout in the event you hit a pothole.
There are also instances where cars can have different-sized wheels, often with a larger pair on the driving axle. This is known as a staggered setup and is common to see on rear-wheel drive sports cars.
The main benefit of larger tyres is that they have a greater surface area which can provide better traction, which is why performance cars often have more rubber over the driving axles and 4x4s will typically come with a set of chunky off-road tyres all around.
However, it’s worth mentioning that the tyre tread can also play a big role in maintaining road grip and overall traction, regardless of tyre size, and one of the first warning signs that a tyre should be replaced is when the tread starts to fade with the raised edges becoming even with the surface.
Keyword: The difference wheel size makes