Not so…
The Speed Rating is 100% about the… “Speed Rating”, and indeed it is about SUSTAINED SPEED, not intermittent top speed capability.
But different countries have different legislation about required Speed Rating on Original Equipment Tyres that are invariably more conservative than any legislation on in-service for after-market replacement tyres, with the dominat legal concern about after-market tyres being correct original DIAMETER and correct original WIDTH and correct original ASPECT RATIO, but with allowances/increments on Width and Aspect Ratio - in Australia you can go one increment wider, and one Aspect Ratio lower and still be legal - thus for an E-type correctly fitted with 185R-15" (thus standard Aspect Ratio - nominally 78-80%) you can fit 195/70R-15" legally, but a 205/70R -15" is not legal, albeit the chances of being picked/up and booked are not high. So if in doubt, check you local rules in USA, Canada, UK wherever…, rules are usually different one country to next with AFTERMARKET safety matters, albeit a lot of uniformity with new Original Equipment safety matters where legislation world wide is moving (not yet there for commercial advantage reasons) towards harmonization.
Also bear in mind that when E-types were introduced, they were factory fitted original equipment with DUNLOP ROAD SPEED RS5 cross-ply tyres of 6.40" x 15" size, with Radial Tyres not yet acceptable to Jaguar at all, and general reluctance/concern world wide (apart from France and Italy), but finally available in UK/Europe cars as original equipment in about 1963, but not in USA/Australia until 1967, and the then DUNLOP SP Sports fitted in UK, were in fact rubbish tyres.
But this all crossed over the period of introducing SPEED RATINGS, as various countries had to be convinced that these new radial tyres were in fact as safe as the current cross ply tyres (called Bias Ply in USA), noting radial ply tyres were first promoted on basis of their long life, and not re any grip/handling/speed capability as is the sole interest/concern these days…
The ‘R’ in the tyre size moulded into the side wall is a legal requirement to advise “Radial Ply” tyre.
The suffix letters in modern tyres, such as the “91V” in the Vredestein advert is the LOAD RATING of the tyre.
Other things like ‘cornering and car dynamics’ have nothing to do with the markings on the tyres, so no quick way of relative assessment, given these relative aspects can and do vary with tyre size and the actual characteristics of the car so fitted, and indeed what performance use/priorities the owner/driver of the car wants…
Personally, for me - the head and shoulders best all round tyre I keep fitting/using on 6 cylinder E-types is the MICHELIN XVS 185HR-15" - so correct original size, H rating 100% satisfactory (and legal in Australia), and Michelin XVS is definitely my superior choice…
Others may have different priorities…
To add to the speed rating conversation a friend had a machine that would spin a tire until it came apart and would record the speed at which it happened. We spun a Michelin vr rated 180 rear motorcycle tire and it didn’t actually come apart until just over 300 mph! I would say the ratings are pretty conservative to avoid any type of lawsuit. And don’t try this at home and come after me for it!
Speed rating is speed rating, BUT, higher speed rating = stiffer sidewalls = better cornering characteristics. David is correct that it will make a difference in handling. In simple terms, to attain a rating of xxx speed, the tire must be able to return to its natural profile before one point makes a revolution and makes contact with the road again at xxx speed.
That is simply NOT a factual statement.
A SPEED RATING is a legally required specific performance characteristic that has no direct relationship with anything else. Things like ‘better performance characteristics’ or other deliberate/specific design characteristics of the tyre, independent of the ‘speed rating’, albeit typically a very high speed rated tyre, is aimed at the top end performance car market that may well also prioritise handling characteristics - but its not directly related. For instance a tyre of the same speed rating, may priorities ride qualities and tyre life, over lateral grip characteristics, and other might prioritise low noise. You will find tread pattern and rubber compound impacts considerably on tyre performace characteristics, albeit “Marketing Priorities” as to what looks good is also a major goal…
And thats the problem - Marketing is the main priority of tyre-manufacturers and tyre retailers, with the car and tyre engineers more concerned about best compromise match of characteristics to suit the car to be equipped and the target car customers buying these cars… Speed Rating is a specific legal requirement, and indeed these days a conservative legal protection, albeit back in the 1960s it was a major technical concern for radial ply tyre manufcaturers - other than Michelin who had invented radial ply tyres in the 1940s, and had mastered their engineering decades ahead of the rest…, albeit Pirelli got into the act in the late 1950s, but way ahead of the British and American tyre manufcaturers…
Wow - the inappropriate and frequent use of capital letters in Forum posts should have its own rating!
The speed index indicates the maximum speed at which a tyre can carry the load indicated by its load index under the conditions of use specified by the manufacturer. Each tyre must have a load capacity equal or superior to half the weight borne by the axle on which it is mounted. Tyres with the same load index, regardless of size, may carry the same load although they may require substantially different inflation pressures to do so. An equal or greater load index does not always correspond to equal or greater load capacity at all inflation pressure settings
A higher speed index tends to mean that the tyre can better cope with acceleration, braking and high-speed cornering. It is strongly recommended to always fit tyres that have a speed capability and load index at least equal to or higher than those originally specified by the vehicle manufacturer.
Relying on the speed rating alone is a rookie error. To quote from an Australian web site:
“Like load ratings, speed ratings are regulated by law. You can’t drive with tyres that are lower than the recommended speed rating. Aside from being illegal, it can cause poor handling and unpredictable steering of your vehicle. You should look at your speed rating and your load rating together when buying tyres, as the two work hand-in-hand (like Vegemite on toast).”
I would add that you should look at the speed index, load index and pressure as the three work hand in hand (like Vegemite and beans on toast). As an example I have 185VR15 91 (91 = 1356 lbs) Dunlop SP Sport Aquajets on my FHC and they are inflated to 38psi for best handling. The 185VR15 93 (92 = 1430 lbs) Michelin XVS on my OTS handle best at 32psi.
H rated tyres on the E-Type are inappropriate and illegal depending on your country/state laws.
This was our thinking. We put Goodyear Assurance on our '64 FHC and I thought it rode just great. We had all new suspension stuff and an exact alignment. Rode like a new car. Then… got a '65 Corvette - same size tires! Didn’t want Goodyears for an irrational reason having nothing to do with the tires themselves. Got some Coopers. Cut off our nose to spite our face. Now the 'Vette rides worse than the Jag in any case, but I suspect the tires are making it worse worse. Anything that would make it ride more like the Jag would be welcome. Unless we go to a track day (unlikely) I just want a smooth ride.
BTW, wife says it rides about the same.
And David, you are still WRONG…, so its seems not “inappropriate” at all…
And why do you confuse the debate about SPEED RATING - with your Dr. Google efforts on LOAD INDEX - they are different, and have different legal implications…
To recap, I did say the aftermarket situation - and that applies to replacement tyres for 50-60 year old E-types - does vary from country to country, and is different for OE for new cars, and thankyou, but I do know the Australian situation extremely well, and indeed also love my Vegemite on toast, but no thanks on the beans… they don’t necessarily go together at all being separate criteria. Can I suggest if you want the facts on these matters, have look at the official Government Legislation (Federal only applies to new cars OEM, so in Australia you need to refer to the separate eight State/Territory legislations, and you of course can advise re the UK situation, and our American friends re the situation in USA with 50 States to consider), and then see if/what Technical Standards then get called up - we all know how inaccurate/misleading the invariably simplistic Dr. Google can be…
In the mean time I will happily and legally continue to use my Michelin XVS 185HR-15 tyres fitted to my [ACT] Registered E-type, that were fitted as aftermarket replacement tyres, not actually being available from Michelin OEM in 1966 in the embryonic days of tyre SPEED RATINGS, and before anyone had thought about LOAD INDEX…
So far as legal requirements in the U. S. go I’ve never heard of any kind of state or federal regulations for an owner to buy tires of a certain speed rating based on the car they are buying the tires for. ZIf such regulations do exist I doubt they are enforced. If you can physically fit it to the car you can drive on it.
Speed Ratings? All I know is what I’ve read, like:
My guess is that the speed ratings of tires used is to protect the liability of a car mfg. or a tire dealer. I have had tire dealers tell me it is their policy to replace tires with like speed ratings as a preference but will go one grade down when pushed.
I believe the speed rating of the original Dunlop tires on my 70 was “V”?
With gearing that limited speed to about 125 mph? I have been using “H” rated tires for many years and since I use 205/70 with a higher load rating and do not use tubes, my guess would lower heat generation. As a layperson, I would think this may result in a greater margin of safety over a typical “H” rated tire.
I have three cars that are capable of near or above 160 mph, my biggest fear with two of the cars is that the tires are so low profile that a pothole at low speed will take it out. My only tire failure after 55 years of driving was with these rubber band tires.
Glenn
Actually the single most important thing about handling, and it is marked on tires, at least in Canada and the US is the UTQG rating, and the lower the number the better it handles. This used to be called tread wear index, and it is generally a number which denotes hardness of the rubber compound. The softer it is the stickier the tire. A racing tire is typically 40, not street usable, at 80 it can be used on the street but not for long. The Vred Sprint classic is 220 which denotes a sticky tire. Some tires are 560 and up eg: Michelin Harmony, which I reckon on an E Type will last to the time the sun becomes a red giant.
Forum and social media etiquette holds that capitalised words are the equivalent of shouting or aggressive behaviour. Using them is totally unnecessary and detracts from your otherwise worthy posts.
Factually wrong. I will try and make this simple:
To test a tyre the manufacturer puts it on a rig and runs it up to its design speed index in 6mph increments at ten minute intervals. The rig imposes on the tyre its design load index and the tyre is pressurised to a nominal psi. As I have said the load index varies with tyre pressure and the speed index varies with the load index (each load increment affects the maximum speed by about 5%). So the triumvirate of pressure, load and speed are inextricably linked and varying one affects the others.
Based on the axle load of each make/model of car the tyre manufacturer can determine the optimum tyre pressure taking into account the speed and load index. Hence the Michelin XVS 185VR15 93 has a recommended tyre pressure of 32psi on an E-Type whereas the Dunlop SP Sport 185VR15 91 has a recommended tyre pressure of 38psi for the same application because they have different load indexes (93 vs 91) but the same speed index. This combination affects acceleration, deceleration and cornering dynamics.
Those four small patches of rubber that sit between you and potential oblivion need to operate in the optimum way optimised for your car. If you choose to ignore the manufacturers research and recommendation that is up to you but please do not encourage others to do the same.
It is socially irresponsible to fit anything other than VR tyres on an E-Type as you need every possible advantage when mixing with modern traffic and the distracted drivers who have probably not noticed your presence.
I do not believe that to be accurate. This was discussed a few years ago and I posted the following information at that time. I do believe Consumers Report information would be accurate. Maybe you just do not agree with them.
"Although I do recognize the somewhat correlation between the UTQG treadwear and tire traction, I do not believe one should buy tires based only on the assumption that if one wants traction, one should shop for the lowest treadwear number. As said, it is difficult to get good information on tires, and we all have our own criteria as to what we desire in a tire. I hate buying tires. Having said that, I do believe Consumer’s Report attempts to be very objective, even if I do not always agree with their recommendations for me. But I will use their data.
I will compare three tires (which I did pick since they support my point):
Michelin Defender 820 Consumer’s Report tested tread life 90,000 mi.
Firestone FR 710 560 Consumer’s Report tested tread life 65,000 mi.
Dunlop Direzza 460 Consumer’s Report tested tread life 40,000 mi.
The Dunlop would seem to have the best traction, twice as good as the Michelin Defender.
However, based on Consumer’s Report actual testing, they rate them:
Michelin Defender Dry braking- very good…… handling very good.
Firestone FR 710 Dry braking- very good…… handling good.
Rating slightly lower the Michelin even though the treadwear rating is much lower
Dunlop Direzza Dry braking- very good…… handling very good
The Dunlop rating is similar to the Michelin even though the treadwear rating is very much lower. And the actual tread life is less than half.
I think it was in the mid 60’s when performance tires started getting wider, and a few years later when they started getting softer rubber. No longer could you run Le Mans on one set of tires. It’s amazing to me that 55 years later we still fight battles over what handles better, wider tires, with soft rubber, or skinny tires with hard rubber, as if we still used the latter on performance cars. I think that people who argue for the latter have never run quickly in an E Type with the former. I don’t dispute what Consumer Reports say about the tires they tested - they are all season tires, none which have any claim to high performance, and what criteria they use for handling is undefined. Nor do I dispute that tire construction can have as or more impact than tread wear index on handling. What is clear however is that if you are looking for a performance tire look at UTQG first.
After 30 + years of racing and autocrossing E Types the only criteria to me about handling is what the stop watch shows. I wish that everybody had the opportunity to drive an E Type hard, while equipped with Avon 205/70-15 CR6ZZ tires with a wear rating of 80. It would blow you away, and they are not even particularly wide.
Terry, I kind of agree with you. I’m looking at some Bridgestone Potenzas that look brand new. But they have aged out. I autocrossed them on a sandy FLA. airport and was amazed at the lack of grip. I’ve had more grip on snow. Quite comical actually. All the local “shoes” were on Hankook, or Hoosier cheater slicks.
So my question is: If don’t need mileage, I need grip and even more important wet grip.
Suggestions?
I have one of those too. From 66 . however, for a spare on which one could drive more slowly on to get to a shop, I’m thinking of a more standard and less expensive size like 205-70, If I spring for Vreds. Save a few dollars. Help pay for new tubes. After all, most cars have donut tires today and those are FAR different than road tires, and they’ll get you there
Just a note if the spare tire is a different size from the rest on the car and used on the rear of the car, the Positrac will complain with different sizes on the same axle. That’s from my experience I had a problem for a while with a ‘leaker’.
. however, for a spare on which one could drive more slowly on to get to a shop, I’m thinking of a more standard and less expensive size like 205-70, If I spring for Vreds. Save a few dollars. Help pay for new tubes. After all, most cars have donut tires today and those are FAR different than road tires, and they’ll get you there