How many of us are guilty of swopping different makes of tyres with the ones that are already on our vehicles to save a few bucks? Having two of one make and two of another make on the different axles doesn’t sound that far off, but what if you have a puncture and the spare is a mis-match?
Bridgestone has advised motorists to ensure all four tyres on their vehicles are of an identical make and tread pattern to ensure best road holding. The tyre company was commenting in the wake of its recent Tyre Check survey which found that tyre-mismatching on vehicles remains a cause of concern.
“Modern vehicles are designed with certain traction characteristics which depend on each tyre having similar performance,” said Bridgestone’s General Manager for Field Engineering and Technical Services, Hiroshi Nakanishi. “When a vehicle is fitted with tyres of varying makes, sizes or tread patterns, roadholding performance could be affected, and the vehicle’s ABS brakes and stability control may not deliver the levels of safety the driver expects,” he added.
The most dangerous type of tyre mis-matching occurs when different tyres are fitted to the same axle. This can cause the vehicle to pull to one side under braking. On vehicles with ABS, the vehicle can compensate at the expense of longer braking distances, but without ABS, the vehicle may enter a sideways skid under heavy braking. Nakanishi compared braking performance with mis-matched tyres on an axle to braking with one side of the vehicle on a wet surface and the other on a dry surface. “Even a small difference in braking traction from one side of the vehicle to the other can affect stability and stopping effectiveness,” he said.
Roadholding can also be affected when one axle is fitted with different tyres to the other. “A vehicle’s road holding characteristics are carefully optimised by engineers, but can be degraded when tyres are mis-matched front to back,” Nakanishi said. “It is rare that different types of tyres give exactly the same performance, so if a vehicle has less effective tyres at the rear than at the front, the vehicle will be more prone to a rear-wheel skid than it would be with four identical tyres,” he said. “Again, modern stability control systems may be able to compensate for this at the cost of reduced road holding, but on a vehicle without stability control, the driver could enter a skid which leads to loss of control.”
Nakanishi said it was very important for drivers of vehicles which do not have electronic driver assistance like stability control or ABS brakes to ensure all four tyres on the vehicle are identical. “Vehicles like these cannot assist the driver to compensate for tyre mis-matching and there is a higher risk of loss of control under heavy braking or during emergency swerves,” he concluded.