Yes you can buy tyres with equal or greater speed ratings than your original equipment tyres.
However, tyre speed ratings make a difference not only with regard to speed, but with regard to ride comfort, wear and cornering ability.
The impact of a higher speed rating:
Typically, the higher the speed rating, the better the grip and stopping power, but the lower the tread life.
The impact of a lower speed rating:
Although we don’t recommend it, if you use a tyre with a speed rating lower than your vehicle’s original tyres, you will reduce your vehicle’s top speed limit to the tyres’ speed rating.
The handling of a performance vehicle may be different when the replacement tyres are not the same speed rating. Refer to the vehicle owner’s manual to identify any tyre speed rating restriction that could affect operation of the vehicle.
Can you mix different speed ratings on your vehicle?
For best performance, use the same size and type of tyre on all four wheel positions. But if you do mount tyres with different speed ratings on your vehicle, make sure that the lower speed-rated tyres should always be placed on the front axle. This is to prevent potential over-steering (your vehicle doesn’t follow your steering, turns more sharply and may spin).
How to read speed ratings:
Tyre speed ratings range from A (the lowest) to Y (the highest). However, the chart is not completely in alphabetical order. For example, H for high speed is between U and V.