Reducing speed ratings?

[190]

I do have a bit of niggle about XL tyre pressures - XL only carries extra load at high pressure. At normal pressures the load capacity is slightly reduced compared to a non-XL tyre, so the pressures should be upped a little.

Absolutely no-one seems to realise or understand this. However the difference is probably within the error range of most tyre pressure gauges so it's not a big deal

I understand that an XL reinforced tyre car can only carry extra load if it's inflated to a higher pressure. But it's all academic because in order to take advantage of the extra load rating a C class would far exceed it's max. gross vehicle weight. In fact last time I looked at standard tyre load tables even their load rating could not be fully utilized without exceeding the gross vehicle weight.

Another thing that tyre manufactureres load tables showed was that MB's recommended pressures appear to have been set higher than needed to carry the load. Presumably that has been done for for reasons of fuel economy or handling.

 

[MB-BTurbo]

It's the Michelin Cross climates I'm looking at. They do come in normal load ratings of 91 but only in H.
Anyway they get excellent reviews and have the bonus of Michelin calling them summer tyres with winter capabilities...very handy when it comes to insurance companies asking to be notified of winter tyres usage

 

[MB-BTurbo]

So I phoned the insurance company...may as well not have bothered, lol. She had no idea what speed ratings or a load index was. She then proceeded to read a list of what they would consider to be tyre modifications. Are they wider? Are they flared (no idea what that means)? Are they winged (no idea what that is either)? Are they stretched? Are they winter tyres?..which doesn't actually increase the premium, so why does it matter?
As nothing was mentioned about speed ratings or load index she didn't want to know. However, the Crossclimates might be considered winter tyres as they have winter capabilities, so I might need to declare them, then I might need to take them off for summer. Marvellous service.

 

[Rory]

It's the Michelin Cross climates I'm looking at. They do come in normal load ratings of 91 but only in H.

What size are you looking at? I'm pretty sure Cross Climate's only come as XL.

 

[MB-BTurbo]

They do a 205 55 16 91H