Question. If my car currently has 'W' rated tyres, I know I can't go lower than that, but how about 'Y' or 'Z' rated tyres? Is that a higher rating, or just a different rating?
I ask as a lot of the tyres recommended by the Which report this year (thanks Cheddar) are 'Y' or 'Z' rated, and I haven't really got an appreciation of what would be suitable.
If not, anyone got a recommendation for what to fit to a Honda Accord Diesel - 225/45 R17 W ?
Cheers,
Gord.
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Question. If my car currently has 'W' rated tyres, I know I can't go lower than that, >>
I fitted V rated (149 mph) Bridgestones to my Mondeo in place of the std W rated Contis (205/50/17), the dealer confirmed that they would be OK and I advised my insurance company in writing to be on the safe side.
I ask as a lot of the tyres recommended by the Which report this year (thanks Cheddar) are 'Y' or 'Z' rated,
Thanks for the acknowledgement, higher rated tyres will be fine, I dont have the report to hand though I have heard that Falkens are very good in the lower profile 50/45 sizes and are well priced.
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Even the lowest rated tyres can cope with the 70mph maximum speed limit. Assuming you stick to it, is there any advantage in fitting higher rated tyres?
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I would argue that you must meet or exceed the vehicle manufacturer's specification as given in the handbook. If you fit an inferior tyre, you might end up on dodgy ground with your insurers if you have an accident which might have been caused by the tyre and your car is inspected.
Number_Cruncher
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If you fit a speed rating below Manufacturer's Recommendation you could compromise the handling of the car at any speed - not just the maximum rated speed.
I believe Insurance would be invalid if you fitted the wrong tyres.
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Check the load rating too.
I wouldn't be surprised if the two ratings are a function of each other anyway.
I read on a tyre manufacturer's website not to get over-specced tyres and they may reduce comfort.
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We have been here before. Citroen have fitted two different speed rated tyres to the C5 2.2 HDI, depending on the model and wheel size. When the C5 was introduced, the SX model had H rated tyres and the Exclusive had W rated tyres. I am sure the W rated tyres were fitted purely because it had the same wheel size as the 3.0 V6. The SX had smaller diameter wheels.
I have had H rated tyres on the rear wheels of our C5 2.2 HDI Exclusive for almost two years now and there is no discernable difference in handling. There is no chance of me getting anywhere near the speed limit of these tyres.
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As ever, I'm no technical expert, but I'm pretty sure that the tyre specification for your vehicle is based not just on speed but also on load, torque, handling characteristics and perhaps other factors too. Depart from that spec at your peril.
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As ever, I'm no technical expert, but I'm pretty sure that the tyre specification for your vehicle is based not just on speed but also on load, torque, handling characteristics and perhaps other factors too. Depart from that spec at your peril.
So tell me then, how can a different model of the same car, with the same engine, producing the same power and torque, require a higher speed rating for its tyres, just because it has bigger wheels?
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Good question, which I can't answer, for want of technical expertise. Have you asked Citroen?
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No, I haven't asked Citroen. To me it is nonsense to have a tyre rated at around 150mph on a car that is never driven much above 80 mph.
I did ask my insurers and they said it is ok if the speed rating is never exceeded. Well, I will never get near it, never mind exceed it.
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Gordon M wrote:
Question. If my car currently has 'W' rated tyres, I know I can't go lower than that, but how about 'Y' or 'Z' rated tyres? Is that a higher rating, or just a different rating?
I've noticed that manufacturers often fit tyres with a higher speed rating than is required according to their own handbook, presumably because they get the right price at the time. I would take the handbook spec as the minimum. W rating is 168mph - I'd be surprised if the handbook specified that as a minimum. If the handbook spec is H or V then you will have a much wider choice of tyres than if you confine yourself to available W rated tyres.
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I think people are getting to hung-up on what a speed rating means...
It has nothing to do with the speed you drive.
The speed rating is actually part of the load rating such as 91V
It has everything to do with the speed used in a failure test in order to award a rating such as T, W, Z or whatever.
Maybe that is why they use letters, to hide the speed from people to stop this correlation and confusion.
A tyre's speed rating is a much more specific way of expressing its ability to dissipate heat compared to its UTQG temperature rating.
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>>A tyre's speed rating is a much more specific way of expressing its ability to dissipate heat...
Absolutely spot on!
Number_Cruncher
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Ashok,
My point still stands doesn't it? - the handbook might specify H rated notwithstanding that the car is fitted with W rated tyres. I was not suggesting that lower rated tyres were OK if you kept below the "speed rating".
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Yes, I agree, but you must make sure both the speed and load ratings are complied with, as one is derived in conjunction with the other.
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Nobody has said why the same car with different size wheels should require tyres with a higher speed rating, given that the load rating is the same and the power of the engine is the same. People carriers with the same engine, which weigh much more than our C5 and therefore put much more load on the tyres, are fitted with H rated tyres. So it is safe to travel at 80 mph in one of these with H rated tyres but not in our C5?
There was an example given in an earlier thread of a Ford Focus, with a top speed of 118 mph, being fitted with V rated tyres. Am I suppose to accept that this car needed those tyres just because the manufacturer fitted them?
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Nobody has said why the same car with different size wheels should require tyres with a higher speed rating, given that the load rating is the same and the power of the engine is the same. >>
They dont require a different rating, it is surely more to do with the availability of sizes of tyre versus the speed ratings, i.e. a wide low profile 17" or 18" is more readily avaialble in higher speed ratings.
People carriers with the same engine, whichweigh much more than our C5 and therefore put much more load on the tyres, are fitted with H rated tyres. So it is safe to travel at 80 mph in one of these with H rated tyres but not in our C5?
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Load and speed ratings are not directly related, i.e. you can get a 91H and 89V rated tyres.
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It is also perhaps a matter of economies of scale in manufacturing in that it is likely to be more cost effective to produce 100,000 tyres with a W rating that 50,000 with a V rating and 50,000 with a W rating.
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