all weather tyres - speed rating and insurance

[monoloco]

Does anyone know for definite about tyre speed rating as far as insurance is concerned? I always thought cars capable of 149mph etc had to have tyres rated to run at 149mph continuosly -ie V,W,Y, Z etc even if there was zero chance you'd ever do that speed briefly let alone continuously. BUT my insurance broker is now saying this isn't the case, so do I believe him?

Reason I need to know is I have a Merc ML420 4x4 (because I live up a steep lane that never gets cleared of snow in winter and I ocasionally have to drive over farm tracks and fields). Now I don't want to drag out the whole 'winter tyre' topic again as it has been done to death elsewhere! What I want to do is fit 'All Weather Mud & Snow tyres'. I know these are a compromise -not full winter tyres or full off road tyres and they won't give the same ultimate grip as summer road tyres on a warm dry road. I don't drive like a loony so something that gives me 90% grip all year is fine and better than 100% in summer and F-all grip in snow or mud. I had them on a Jeep I had years back and they were great.

Trouble is the choice of M&S 'Z' rated tyres or above is very restricted and the only ones I can find in my size only come in 'H' speed rating (130mph continuous)no decent maker does M&S/All Weather tyre in the same size (265/50/R19+XL load factor) with a Z or above. I've found some decent Continental M&S 4x4 tyres that are described as 80% on-road and 20% off-road and have the right profile/rim/load factor but only come in 'H' speed rating. I tried to ask the insurance company (Aviva) direct if I could fit these to a car capable of a theoretical 149mph but they wouldn't talk to me and just referred me to the broker. The broker's email answer was:

"In respect of your query as long as your tyres are road legal to be used on UK/EU public highways , then you have no issue. In all honesty as long as tyres are road legal and do not alter your vehicles mechanical settings you need not notify us or your insurer. Please note any other adjustment to the suspension, wheels or mechanical parts of your Mercedes will have to be disclosed"

So, does anyone know for certain? I need an answer fairly quickly as the current tyres are on the wear markers!

[Trevelyan]

I can only refer to my experience when talking to my insurance company about changing tyres - to winters in my case. My car normally has W rated tyres fitted but a lot of winter tyres only come with an H rating. My insurance company weren't bothered if I wanted to drop to H, their only stipulation was that the load rating of the tyre (96) didn't change.