It’s funny how often wheels and tyres go overlooked, despite the fact that they’re both one of the most vital elements on your car.
For a great many people, tyres are simply bits of rubber that get replaced every time the tread depth wears out. Even amongst car fans, tyres are probably the one bit of kit most often ignored and only really come into discussion when somebody wants to swap their alloys.
But if you’re planning on swapping either the wheels on your car or the tyres for some different ones, there are several important things that you must know, for the sake of your car’s health, your wallet and potentially even your safety.
What’s the benefit of different wheels and tyres?
First of all, let’s take a look at some of the benefits of changing the sizes of your wheel or your tyres. The most obvious benefit is purely aesthetic; some car fans may want to modify their cars with aftermarket wheels or low-profile tyres for a sportier, tuner-style appearance.
Drivers who often go off-road may also want to swap their standard setup for smaller wheels with larger, knobbled tyres to increase grip in slippery conditions, while others still might choose to enlarge their wheels to increase the contact patch with the road.
Bigger, wider wheels can accommodate wider tyres with a larger diameter, which will mean that more of the tyre’s surface area will be touching the road below it, theoretically increasing grip and thereby handling.
A larger contact patch can improve grip, cornering and braking performance, but it’s worthwhile bearing in mind that grip is only marginally increased by new wheels and tyres. In most cases, simply selecting tyres made with a gripper compound will work wonders for the car’s performance.
What are the downsides?
While there are plenty of good reasons why you might want to change your wheels and tyres there are also plenty of downsides and pitfalls that you need to be aware of before you buy or swap anything.
For a start, larger wheels will give more unsprung mass to the car, which is the weight of all the components linked to the wheels and suspension but which aren’t supported by them.
The more unsprung mass, the more of a detrimental effect that weight will have on the car’s handling. Instead of enhancing performance, you could find that bigger wheels and tyres only slow you down and can also increase fuel consumption by as much as 10 per cent.
Really big wheels or large tyres can also impact against the inside of the wheel arches and scrape against other components, which is potentially dangerous particularly when cornering. Larger wheels typically also bring a marked reduction in ride quality, firming the car up and transmitting bumps and cracks in the road into the cabin.
Finally, another downside is cost, as bigger wheels and larger tyres are invariably more expensive than their smaller equivalents. Even if you’re prepared to foot the bill, tyres with small sidewalls are more prone to failure, meaning you could have to pay out more money, more often.
Is there anything else important worth mentioning?
Yes, now that you bring it up. The geometry of your car’s suspension was set up specifically by the car’s manufacturer to handle a particular size of tyre and a particular size of wheel. Changing sizes can risk affecting the handling of your vehicle at a critical level.
Furthermore, when the diameter of your wheels and tyres are different to those that it came from the factory with, both your speedometer and odometer will have erroneous readings, which could get you in trouble with the law, or effect everything from resale value to insurance costs.
It can also effect the car’s steering and braking systems too, as both will have a harder job with larger wheels, while the braking pads and discs will wear out much quicker than they would with standard-sized wheels.
I still want to change my wheels and tyres, what do I do?
If you still want to go ahead and fit your car with wheels and/or tyres of a different size, the first thing that you should do is check which size combinations your car is offered with from the factory.
That way, you’ll be able to know which sizes you can get away with without damaging your car, causing unnecessary wear or impacting on safety. If you’re looking for bigger wheels for performance, seek lightweight aftermarket wheels and performance tyres too.
Usually these are more expensive and come from specialist brands, but don’t be tempted into something which looks similar from a knock-off brand, as these will be nowhere near as durable or as good as the real thing.
It’s also important to just be sensible. You might think that your car will look awesome with 21-inch alloy wheels, but if it can only accommodate 19-inch wheels then get the smaller size. Even if everything else on your car runs perfectly, outlandish wheel and tyre combinations will wear it out quicker and more often than if you’d stuck with something more reasonable.
Finally, unless you’re an expert it’s worthwhile calling in at a shop or a garage to ask for advice or to get them to fit the wheels for you, along with any modifications to your car’s set up that will be necessary to fitting the wheels safely.
Choose a reputable shop, and if you’re lucky you’ll get some free advice even if you don’t buy anything from them. Ask politely, be considerate and most of all pay attention to what the mechanics have to say: if the professionals say it’s a bad idea, then it’s definitely a bad idea.
If you liked this article, why not check our Car Keys guide to changing a car tyre?
