The greatest risk to a tyre is speed and I suspect that the forces are exponentially linked to speed.
Agreed. According to the testing protocol, the tyres are tested on a rotating drum and need to survive for 30 minutes at a given speed to become rated for that speed. I presume that the test is carried out at the maximum load and suitable pressure.
After that I can only repeat what I have already stated. When, if ever, an assessor asks why the tyres are not correct rating just point him to the tyre fitters and plead ignorance. I must see 25 - 30% of all cars with incorrect load and / or speed ratings and I know the owners wouldn't even know a load rating existed.
Agreed. people are ripped off all over these days. If my unknowing daughter goes to a tyre fitters who tells her the tyres are good she has no way of knowing. By going to a tyre fitter you can presume level of due diligence, because you didn't try to do it all yourself in the garage.
Also I suspect the safety margin is enormous.
30 minutes of test at the rated load is enough, probably. if yoiu bring the load down the speed can be increased usually, according to the testing protocol which acknowledges the effect of increasing speed causing more stressand reducing the load rating accordingly.
But first and foremost you have to consider if your car can even travel at the speed which the tyres are rated for.
I should have speed rating W, 168mph tyres, but have only speed rating V 149mph tyres.
My car can only travel at 131mph (so just out of the H - 130mph speed rating bracket)
The load rating in the manual seems to suggest that for all tyre load ratings a factor of safety of 2 has been applied - in other words the unladen weight of the car is almost exactly half of the load rating of the tyre. Even fully loaded there is more than a 10% spare capacity...more like 25%
Considering your thread above you suggest that load and speed ratings are not part of the MOT for passenger cars. If that is the case it suggests that the government don't consider it a serious safety issue for these vehicles. Again how is the average guy in the street meant to know.
That's probably the best point of all IMHO. The MOT tester won't tell you if it's wrong, so how is the average person supposed to know ?
Finally, as before I am not an expert and do not condone deliberately fitting incorrect tyres but if I bought a car privately with a tyre rating that was wrong I would not rush to get them changed, I might use it as a haggling point but behind that provided they were a big brand I wouldn't worry. If it was a forecourt purchase I would insist on them being changed or get a decent discount.
I even think calling them 'incorrect tyres' now is a misnomer.
i think you're safe to assume that as a consumer, if a tyre is load rated for 500kg and 130mph that you can load it to 480kg and drive it at 125mph all day long. If it falls apart then the manufacturer is liable.
Does everyone know that if yoiu have a puncture repaired then the ECE 30 regulation and it's derivitives suggest that whatever it's rating before, it should not be considered to be speed rated for anything more than 85mph. How many people who worry about insurance assessors know that ? If yiou have a puncture repaired shouldn't yoiu be informing the insurance company that yoiu have an incorrect speed rated tyre ? Will your insurance be voided if the assessor sees a repair on the tyre ?
I know insurance companies like to have their wriggle room, and like most people I've been a victim of it, but you have to come back to common sense or you'll go mad from worrying. So if a tyre is hugely over rated as per it's markings and ECE 30 testing but is a tad 'slower' than that recommended by the car manufacturer I really don't think an assessor is going to be too bothered.
I'm still looking to hear from anyone who had an insurance claim refused on the grounds of using a tyre with a speed or load rating below those as recommended by a manufacturers guidance notes on tyres in the manual.