The Michelin Pilot Primacy tyres that I bought last year for my Mondeo were rated at 87W.
However, the one's that I purchased more recently were rated at 87V.
Have Michelin downrated the tyres for some reason, or has the rating system been recently changed? I would be very interested to know.
Galaxy
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The Michelin Pilot Primacy tyres that I bought last year for my Mondeo were rated at 87W. However, the one's that I purchased more recently were rated at 87V. Have Michelin downrated the tyres for some reason, or has the rating system been recently changed? I would be very interested to know. Galaxy
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The answer to your question is no, the rating system hasn't changed, as far as I know. V rated tyres have speed limit of 149 mph, which is more than enough for your car, I would think (depending upon the model you have).
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Galaxy
It's not uncommon for two different speed ratings to be available from the same maker at a particular tyre size.
JS
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In answer to the original question, providing the maximum speed of the car is lower than the tyres speed rating you are OK.
To answer cheddars point, the speed rating has nothing to do with torque. A tyres rating is the maximum speed it was safe to run that tyre at maximum load. The differences Cheddar is seeing are most likely due to changes in the rubber.
Joe
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In answer to the original question, providing the maximum speed of the car is lower than the tyres speed rating you are OK.
The vehicle may be OK
BUT. How will the Insurance company view it in the case of a claim?
If they register that the tyres fitted are not the same ratings as specified by the manufacturer will an escape clause be triggered?
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If the manufacturer recommends that "W" tyres are fitted, then I guess so. Otherwise I hope not as I always go by the cars theoretical speed plus a safety margin.
Joe
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If it's different to the manufacturer's recommendation then I guess technically it would be a modified car. I woulnd't see anything wrong with this providing you told the insurance comapany who I would be very surprised at if they raised the premium.
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Adam
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I checked with my insurers (Saga) and their underwriter stated that, as long as the car is not travelling at a speed in excess of the tyres' speed rating, there isn't a problem. Personally, I believe that is as it should be. If a manufacturer wants to specify a tyre with a speed rating greater than that which is required, that is their choice. However, I don't see why a tyre with a lower speed rating shouldn't be used, if the car is not capable of exceeding the speed rating. I am never going to get near to the maximum speed of the car anyway.
Our Xantia 1.9 TD was supplied with H rated tyres and yet the top speed of the car is almost 20 mph below the speed rating of the tyres.
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The speed rating is the maximum speed at which the loaded tyre will travel at for one hour without deforming/failure.
However, it is generally regarded by manufacturers that a safety margin of 30Kph (19mph) should exist.
What I do wonder though, is if this test is with a new tyre, what about a 3 year old worn tyre on a second-hand car that may have bumped up kerbs weakening it's textile layers?
Also, say your handbook says V rated, but you decide to put H rated on, and the tyres are 3 years old, and you are going at 80mph on the motorway and hit an object in the road, it may just prove to much and they tyre may fail?
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The speed rating is the maximum speed at which the loaded tyre will travel at for one hour without deforming/failure. However, it is generally regarded by manufacturers that a safety margin of 30Kph (19mph) should exist. What I do wonder though, is if this test is with a new tyre, what about a 3 year old worn tyre on a second-hand car that may have bumped up kerbs weakening it's textile layers? Also, say your handbook says V rated, but you decide to put H rated on, and the tyres are 3 years old, and you are going at 80mph on the motorway and hit an object in the road, it may just prove to much and they tyre may fail?
So there isn't a safety margin built in with the speed rating then? Are you suggesting that one can't rely on a 130 mph rated tyre at 80mph?
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In answer to the original question, providing the maximum speed of the car is lower than the tyres speed rating you are OK. To answer cheddars point, the speed rating has nothing to do with torque. A tyres rating is the maximum speed it was safe to run that tyre at maximum load. The differences Cheddar is seeing are most likely due to changes in the rubber. Joe
I agree, I had some "Z" rated Bridgestone potenzas on my Mondeo and they wore out after 7K. The torque put out and the weight of the vehicle are more to do with the load rating of the tyre than the speed rating, The Mk3 mondeo requires "extra load" or "XL" tyres (about 650-680kg IIRC).
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In answer to the original question, providing the maximum speed of the car is lower than the tyres speed rating you are OK.>>
Yes, legally though you should advise your insurer if fitting tyres of a different size and/or rating than that fitted as standard by the manufacturer.
To answer cheddars point, the speed rating has nothing to do with torque. A tyres rating is the maximum speed it was safe to run that tyre at maximum load. The differences Cheddar is seeing are most likely due to changes in the rubber.
No, manufactures will fit tyres with a speed rating far in excess of the maximum speed of the car because of the loading that the car places on the tyres. Weight is a key factor as is the amount of torque fed through the driven wheels. Many turbo diesels are fitted with higher rated tyres that the petrol equivelent for this reason even though the petrol might have a higher max speed.
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I suppose tyres are made in as few rating as possible, it would be daft for Pirelli or whoever to make a 50 isotopes of one size of tyre, when just 2 or 3 will do. They will probably assess the weight and performance of vehicles which require that size of tyre and make 1, 2 or 3 variations as a compromise. So if you have a slow car with 225/55/16 tyres, and most with that size are fast and heavy, you will be lumpered with high speed/load tyres.
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If I have a tyre with the same load index but lower speed rating, I can't see a problem, as I am never going to get near the speed limit of even an H rated tyre. Even at 90 mph, the car would be travelling at 40 mph less than the speed limit of an H rated tyre.
If torque is so relevant, surely this information should be provided by tyre manufacturers. In addition, if it is so relevant, then surely it is only relevant in relation to the driven wheels.
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cheddar
Quite so, and it's not just torque. The tyres must also match the braking, cornering and handling capability of the car. All of these are safety related and not necessarily related to speed at which they are used. Tyres are an integral part of the suspension and the makers take thier spec. into account. This is why sometimes speed ratings don't always exactly match apparent performance limits.
JS
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So, what is the use of a speed rating if one can't use it to assess a tyre's suitability for use on a particular car? Different tyres give differing performance characteristics anyway, even with the same rating. Are you saying that a tyre with a lower speed rating will be inferior even when driven well within its speed rating?
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Well, you can certainly do the first by fitting tyres with the speed rating that the makers intended. The minor differences between brands has some effect, but all are designed for the loads that the car can apply to them, acceleration, braking cornering etc. Yes, in some ways the lower speed rated tyres are 'inferior' - they are not designed for the same loads as the higher rated tyres. On the right car, which doesn't overstress them, they are fine.
JS
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Logically, the higher stresses that the higher speed rated tyres are designed to withstand, are generated at higher speeds. What I don't understand, is the supposition that some cars will generate these same excessive loads at speeds which are lower than the speed rating of the tyre. If this is the case, this information needs to be made available to the motoring public in a standard format. It is no good putting information on a tyre that says that the tyre will run up to a certain maximum speed, at a certain load, if it doesn't hold true for all types of car. Given that all other factors match the tyre to the car, in particular the load index, a tyre with a lower speed rating should be able to cope with the forces generated up to its speed rating. Certainly speeds of 70 to 80 mph should be no problem for a tyre that is rated up to 130 mph, otherwise we need a whole new system of rating a tyre's performance. What about spacesaver tyres that are supplied with many cars? They are usually limited to about 70 mph, but still have to deal with all the other forces that the car generates at that kind of speed.
What also has to be remembered, is that cars are sold to countries with differing speed limits and so have to be able to deal with being driven at their maximum speed in some countries. These speeds just do not apply in the UK (certainly not with my car).
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There are different types of stress applied to a tyre, high speed generates a centrifugal force, an engine that generates high torque applies a twisting force to the tyre sidwalls, cornering applies a different type of stress again, if all these were accounted for individually when selecting tyres there would be a different spec tyre for each derivative of each model, clearly impractical. The the speed rating and load rating are catch all ratings, some cars, perhaps MPV's, may require a higher load rating though a lower speed rating, others, perhaps a Lotus Elise, may require a lower load rating and a higher speed rating etc etc.
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Yes, it is logical that a lighter car will require a lower load rating and a higher speed rating, if it is capable of a higher speed. So applying the required load index is logical but does a vehicle need tyres with a speed rating 40+ mph in excess of its maximum speed, never mind the speeds that are applicable on the UK's roads? The analogy that you use for an MPV, which may have an engine with the same or greater power, suggests not.
In addition the forces that act on the front and rear tyres of a front wheel drive car are very different. The rear wheels are not subjected to any torque, nor do they bear the weight of the engine to any degree. So, in general, the rear wheels in this instance will be subject to much lower forces. Also, speed doesn't just apply centrifugal force to a tyre, as the faster a car is driven under cornering, the higher the lateral force that will be generated.
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Tyres are amazingly complex for at least these reasons;
1) They are of composite construction, reinforcement, belts and 'rubber'
2) They include rubber which is a very complex material to design for - much more difficult than metals for example.
So, to be able to have a rating that will apply to all types of car, with differing loadings is, perhaps, over simplification, but the alternative - having bespoke tyres for each car doesn't bear thinking about!
The reason for the rating is a temperature limit. Because of the hysteresis of rubber, as the tyre deforms back and forth, some of the elastic energy is converted to thermal energy, i.e., heat.
If you deform the tyre more, you put more heat into the tyre. This is why if you touch a tyre that has been run with too little pressure in it, it will feel hotter than the others. A fair number of the truck tyre treads which peel off on the motorway are caused by the bond failing at high temperatures rather than being 'duff' remoulds.
If you deform the rubber again before it has cooled down - i.e., you run the tyre too fast, you allow the tyre to overheat.
There is also a dynamic effect which can occur at overspeed. A standing wave occurs - owing to the large deflections there is rapid heat build up, and the tyre fails very quickly. This dynamic effect is so fast, the standing wave only exists fora few seconds before failure.
number_cruncher
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The Speed Rating is a Speed Rating, the manufacturers must choose a Speed rating which denotes that a tyre is suitable for all sorts of demands that model of car makes on a tyre. they would not choose a higher rating for the hell of it, as this would sacrifice ride comfort. I can't understand why a layperson would think they know better than the tyre companies and motor manufacturers. It's not as though a scrimp would gain anything, as the difference in price is negligible, indeed, some lower speed rated tyres are more expensive, as they're made in smaller quantities.
Having said all that, is that is that V rated tyre really different to that same make/type/size of ZR rated, or are they both Z to save on tooling? As I don't see why a ZR rated could not be sold as any rating that is lower such as V.
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The Speed Rating is a Speed Rating, the manufacturers must choose a Speed rating which denotes that a tyre is suitable for all sorts of demands that model of car makes on a tyre. they would not choose a higher rating for the hell of it, as this would sacrifice ride comfort.
So it is not just a speed rating then?
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All very impressive I am sure, Number_Cruncher but I am not suggesting having bespoke tyres for each car or running tyres at overspeed (the exact opposite actually). I merely suggested that a 40+ mph safety margin might be a bit excessive.
Is running a 130 mph tyre at 70 to 80 mph really going to overstress it?
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All very impressive I am sure, Number_Cruncher but I am not suggesting having bespoke tyres for each car or running tyres at overspeed (the exact opposite actually). I merely suggested that a 40+ mph safety margin might be a bit excessive.
I wasn't replying / disagreeing with any of the points you had made. I was merely suggesting that owing to the complexity of tyres, some necessary simplifications or rationalisations have to be made which results in some apparently anomolous specifications.
Neither am I suggesting that anyone fits tyres other than those specified by the manufacturers.
number_cruncher
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I am trying to make a rationalisation myself, Number_Cruncher, based on the fact that I won't be driving the car at anything like its maximum speed, therefore at nothing near the design limits of the tyres.
The law restrains my speed to a maximum of 70 mph (80 mph if one wants to use the unofficial motorway speed limit). The manufacturer has to specify tyres capable of capable of coping with the maximum speed of the car, which is irrelevant on UK roads.
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It is interesting to note that Michelin recommend H rated tyres for the 2.2 HDI SX, which is basically identical to the Exclusive (which our car is), except for the wheel and tyre size.
They also recommend H rated tyres for the 2.0 16v, which has a top speed in excess of 130 mph.
www.michelin.co.uk
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