It is recommended that all four tyres be of the same size, construction and speed rating. If tyres of different speed ratings are mounted on a vehicle, the vehicle speed capability will be limited to the lowest speed-rated tyre on the vehicle. It is recommended that the lower speed-rated tyres be placed on the front axle. This should be done to prevent a potential over-steering condition. Vehicle handling may also be affected.
When a vehicle has different tyre dimensions fitted to the front and rear axles, it is said to have mixed tyre fitments. Many powerful vehicle models now come factory equipped with mixed tyre fitments. In addition to the sporty aesthetics this configuration provides, mixing tyre sizes also increases driving safety. While rear-wheel drive benefits from the improved grip of a wide footprint, smaller front tyres help keep the car safely on track (the narrower the tyres, the easier the steering). However, a disadvantage of this configuration is that tyres cannot be rotated axle-wise during seasonal tyre changes (a practice that would be beneficial for even tread wear).