Often many people are tempted to use different sized tyre on their vehicle to improve the look of their car or to benefit from cost savings or promotions offered by tyre retailers. However, enhanced style and financial savings may be short-lived due to the cost of repairs to your vehicle caused by using the wrong tire size.
Firstly, all the tyres on a vehicle should normally be the same size for the vehicle to handle properly and prevent damage. If not the driver will experience not only handling and tyre wear issues but also damage to the suspension and other parts of the vehicle.
When it comes to the question of changing all four tyres to a different size this is possible, however there are several factors to consider before doing and as cars become more reliant on electronics rather than mechanics these factors are certain to increase.
ABS System – Firstly, with vehicles equipped with ABS, using different tyre size and aspect ratio to those recommended by vehicle manufacturers could affect the ABS system’s ability to detect and prevent skids. The ABS system relies on sensors that measure wheel rotation so changing the tyres will affect the original calibration of the sensors therefore reducing the overall safety of the vehicle.
Speedometer Readings – Changing the size of tyre could also affect the speedometer and therefore the mileage of your vehicle. Oversize tyres will make you appear to be going slower and not as far, whilst undersize tyres will appear to increase your speed and mileage unless they are re-calibrated to the new tyre size.
Electronic Gearboxes – With vehicles with an electronic automatic gearbox, a different tyre size could affect the transmission shift points as the electronic wheel sensors contribute to the electronic switchboard that determines when the engine shifts gear.
This doesn’t mean it’s not impossible to change tyre sizes but you should maintain the overall tyre diameter and load capacity as recommended by the manufacturer.
One thing you can change within the above parameters is the aspect ratio of the tyre, basically the overall diameter of the wheel is the same but it gives you the opportunity to see less tyre and more alloy! Generally, shorter aspect ratio tyres are known as high performance tyres as they tend to lower the vehicle ride, have a broader tread and put more down on the road to improve the handling experience. A tyre’s ability to support a load is determined by the tyre’s air volume so if you go to a lower aspect ratio tyre the tyre must be wider to maintain the air volume and load capacity.
Having said all this the manufacturer’s recommendations are there for a reason and they have already chosen the optimum tyre size, aspect ratio and load capacity for that vehicle and normally with good reason. So unless your an expert yourself then I would leave the choice of tyre size to the experts and in my opinion a cars style should never override the importance of safety.