The speed rating for the tyre is the maximum speed a tyre can sustain under its recommended load capacity.
Speed ratings are based on scientific tests where the tyre is run at speeds in 6.2 mph steps in 10-minute increments until the required speed has been met. The speed rating can be found on the tyre sidewall as a single letter after the load index. Do not exceed the speed rating and wherever possible do not fit tyres of different speed ratings. Choosing a tyre with a lower speed rating than recommended by the vehicle manufacturer can invalidate an insurance policy.