What is the legal / insurance position with regard to...
Thank you for your question.
The letter is an alphabetic code that corresponds to the maximum speed at which the tyre can be used (not that you would really drive at 168mph).
On a legal level, you are not permitted to reduce the speed index of the tyres you use. You are allowed to mount a higher speed index (than the original mounting on your car defined by the manufacturer), but not a lower one.
As for winter tyres, you can reduce the speed index of your winter tyre (compared with your summer tyre). European legislation allows you to go as low as the Q index.
So, to summarise, you may reduce the speed index for a winter tyre, but not a summer tyre. In this case it would not be legal to put an H or V rated tyre on your car.
If you need to find a new tyre, we would recommend using our homepage www.rezulteo-tyres.co.uk to compare tyres that would be ideal for your vehicle.
The rezulteo team