Tire speed rating and car behaviour

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Jul 29, 2003
Kyiv, Ukraine
Need your help. May be somebody knows what will be changed in car behaviour if to use the same brand tires, but having different speed rating: H, V and W ? Suppose, you will never exceed 200 km/h. How will speed rating impact cornering, breaking, comfort, mileage and tire life ? Another question, is there a quality difference between tire bearing OEM spec (like MO for MB and N-spec for Porsche) and tire without it ? Thank you in advance for your posts.
As a general rule, in the same model tire, a tire with a higher speed rating will have stiffer sidewalls, possibly stiffer belting, and softer tread for more adhesion. Thus, going to a lesser speed rating may directionally affect handling, braking and cornering adversely, while improving ride comfort and tire life. That being said, I myself replaced original equipment V rated tires with H rated tires with a larger outside diameter on an older high performance sedan because such a change was consistent with the way the car is presently driven, was cheaper, and gave a longer expected tread life.
Primus, I think I can give a good example: Some entry-level Volkswagen Golfs/Jettas(99-05)come equipt w/Goodyear Eagle LS(195/65HR15) as original equipment. But the Eagle LS is also available with a "T" speed rating in the exact same size. Many unknowning Golf/Jetta owners replace thier OE Eagle LSs with the "T" rated version(the "T" is also cheaper) only to find the high speed handling of the car greatly diminished. I've had the opportunity to compare the difference between the two in a back-to-back driving test. At low speeds and on smooth road surfaces, I couldn't tell any difference. But as soon I put my foot down in the twisties, it was clear that the H rated tires were superior. As far as the special tire ratings go, I know Porsche does contract tire mfgs to develop special tires specifically for thier vehicles. Since it is costly for tire mfgs to develop completely new tires for one vehicle, they opt to make subtle changes(in compound and/or structure) to tires already in their existing line-up to meet Porsches needs. [ March 26, 2006, 03:29 PM: Message edited by: Brikhead ]
Goodyear also does this with their Eagle RSA's which are OEM spec'd on some vehicles. Some are T, H, or V rated. You have to be wary of which kind you get. As a general rule, you should NOT downgrade the speed rating of the OEM tire. Also, as a general rule, the higher the speed rating, the better handling (cornering), braking, and acceleration but the lower the treadwear. These H, V, and Z (as a group) tend to handle heat better as well. Tire manufacturers are making better tires in higher speed ratings with longer treadwear in touring type tires. Should you choose to run mixed radials, the speed rating of the lowest should never be exceeded. Just because you have Z rated tires doesn't mean that your vehicle is even able to obtain the rated speed, the manufacturer spec'd them to increase the cars performance or is in bed with the tire mfg.
Thank you for your prompt replies. Today I saw CSC2 205/55 HR16 MO FR ML on the shelves. Necessary to say that CSC2 are quite rare here and, especially, in MO-spec. CSC2 were in my focus since last year, but I could not find them in time (a special single order would require a lot of money). Now they are available (may be Conti started to get rid off because of CSC3 launch ?), but in "H" rating. In fact, exceeding of 200-210 km/h limit happens too rare and I would endure such "defect". But it's very interesting to understand what to expect in their overall performance. If "H" comfort and threadwear come in detriment of handling and braking, then, may be, they are quite similar to PremiumContact2 in "V". Another point is MO-spec. I always though OEM-spec tires are better then just replacement ones as for raw materials use and quality control. May be I'm mistaken, but think what's good for MB, should be OK for Mazda too. Interesting, but if to believe Tirerack info, the weight of H, V and W tires are equal. This is not usual. 205/55..HR16...91H..SL..Mercedes..280..AA.A..21..lbs 205/55..VR16...91V..SL.................280..AA.A..21..lbs 205/55..VR16...91V..SL.................280..AA.A..20..lbs 205/55..WR16..91W..SL..Mercedes..280..AA.A..21.lbs 205/55..WR16..91W..SL................280..AA.A..21..lbs It will be really difficult to take a decision without hearing your views, BITOGgers.
While there's a general rule that you should NOT downgrade the speed rating of OEM tire, there are some really absurd tires being put on inexpensive cars. For example, H rated Michelins are OEM on Hyundai Elantras. The construction of higher speed rated tires basically involves reducing the rubber in the sidewall and tread, which reduces heat buildup, and stiffening the carcass, which reduces flex and also reduces heat buildup. In return the tires are more susceptible to curb damage and get lower tread life. What a deal! In all honesty there is little difference inherent in these changes that impact handling. OEM spec tires are generally a standard tire line "optimized" as part of an OEM deal with a car manufacturer. This may involve slight changes in tread, carcass, and rubber compound to the OEM specs. Within the operating envelope of your driving, dropping down a speed rating or two shouldn't hurt anything. Generally you can "crispen" steering response by increasing inflation pressure, so if the overall design is comparable to the higher speed rated tires, there should be little degradation in handling.
Mickey_M makes some good points. Once again, there really is no cut and dry to anything related to tires. As a vehicle owner, you have to find what's right for your vehicle and driving style. Some shops will flat out refuse to install lower speed rated tires than what's OEM. Also, OEM spec'd tires are "usually" lower quality than AEM with maybe the exception of high end vehicles. A prime example is my 04 Tacoma with 205-75-15 Firestone Wilderness HT's rated at B and B (traction and temp respectively). Different sized AEM Firestone Wilderness are A and B and most AEM in the same size are A and B. I've seen OEM Bridgestone's with a treadware of 100 while the same size and model AEM Bridgestone is 300+. Usually cost is the big decision on what tire goes on what vehicle.
How will speed rating impact cornering, breaking, comfort, mileage and tire life ?
Years ago I had Conti Sport Contact tires on my VW. They were W-rated. I drove a relative's car (same model car) that came with H-rated Conti Sport Contact tires. Even at only 60 mph the W-rated tire felt totally different. Because of that, I put only V, W or Z-rated tires on my cars.
Another question, is there a quality difference between tire bearing OEM spec (like MO for MB and N-spec for Porsche) and tire without it ?
Primus, for example, there are several versions of the same Conti Sport Contact 2 available. They say OEM BMW, Mercedes, VW, Porsche, etc. There are differences in treadwear, load rating, weight of the tire, design (lettering) and differences in how the rim protector bead looks. The speed rating may also differ. You can of course put an OEM tire fo a BMW on a Mercedes, as long as the tire meets the proper specs. For example, if I buy tires for my Audi, I pick the least expensive 205/55/16 W-rated Contis with a treadwear of 220 I can get, even if the are OEM Mercedes tires.
I agree just because a car comes out of the factory with V/H rated tires does not mean that is best replacement solutions. For example Honda Accord owner with V rated tires. Depending on the person they may rarely speed in the 1st place. Second, a replacement set of Michelin Energy MXV4+ may run him 700$ installed. I would tell him personally skip the price tag and consider H rated GY Triple Treads, Comfort Treads or even BFG Traction TA's. In addition these tires will last him/her much longer and a much better rain/snow traction benefit. European car owners are best fitted with H rated tires as a minimum IMO.
Thanks a lot all who participated in this discussion and shared their knowledge and experience. Opinions are quite mixed that, may be, usual for such cases. So, my decision will not be easy. If CSC2 are available in "V" ! Think "V" would be enough: actual engine and our crappy roads will not allow to fully use the potential of all these Z, W and Y tires. But, sellers here don't import Conti on a regular basis cause of its purchasing price. Strange enough, but like Michelin in Germany Continental is priced higher then other brands in our region. That's why, tire sellers import only what they may get at some discount. And that's why, may be, actual tires are in "H". I did not install such tires during last 10 years (the last ones were Michelin TRX in 1994), so I already forgot how they work. BTW, there was another thead here about tire test made by Car & Driver and after I re-read it I found interesting comment on MO-spec: "A week after out testing, Pirelli called to say there's a different version of the Asimmetrico that would have performed better. This version is noted by a hard-to-see "MO" that's embossed on the sidewall (it stands for "Mercedes spec." identifying the line of cars it was designed for), and it uses a different compound than the one we tested."
"Different compound" is quite likely. For example, the Conti Sport Contact 2 for Porsche has treadwear 160, the one for VW has treadwear 220. When picking my Conti tires, I go, beyond model and size, by treadwear number and speed rating.
Here you have to use tires that can cope with your cars maximum speed. This applies to summer tires. If you use M+S or winter tires, you can use whatever you like.. Speed limit here is maximum 70 mph.
Originally posted by moribundman: For example, the Conti Sport Contact 2 for Porsche has treadwear 160, the one for VW has treadwear 220.
Hmm... looking at all the CSC2 available on TireRack, they all have a 280 treadwear index. [Confused]
Sorry Pete, 280 it is. I'm awful when it comes to remembering numbers. But last year I sent 2 Conti Sport Contact 2 back that had the 160 Treadwear rating. Or maybe that was three years ago and still the previous generation Conti Sport Contact tires? I suppose it's possible, but dang it, they sent me the wrong tires! [Razz]
Okay, I checked. The Conti Sport Contact is available with treadwear 160 or 280, depending on speed rating and/or on for which car the tire is. Conti is driving me nuts with their multitude of versions. Even the tirerack guy said he couldn't tell the cosmetic differences (rim protector bead and lettering design) by looking at the site. I always end up calling to make sure they send the correct tires.
I've sometimes been told that one MUST or SHOULD always run tires with the speed rating recommended by the manufacturer or the speed rating on the tires that came stock on the vehicle. So its good to see an informed discussion of the subject, based on facts, and not based on such things as myths, what so-and-so said, what others want us to believe (in furtherance of their hidden motives), fears of groundless lawsuits, the macho attitude that since one's car can do 140 mph one runs and needs a tire rated for that speed, and hand me down hearsay. The tire speed rating is the maximum SUSTAINED speed that the tire (not the vehicle that the tire is on) is capable of so long as the load rating of the tire is not exceeded. Sustained speed does not include such things as passing someone or driving for another reason for a short period of time. The speed rating of a tire has everything to do with how fast you are going to drive, and so long as you do not exceed the speed rating of the tire (and the tire's load rating) you do not have to run tires that match the top sustained speed that the vehicle is capable of. For example, yes, if a Corvette or Porsche is capable of 160 mph, and you are going to drive that fast for SUSTAINED periods of time, its highly advisable to run a W rated tire, which is rated for 168 mph. However, if you are going to stick to the posted speed limits (and as far as I know that's 75 mph or less throughout the U.S.) or do not go more than, say, 20 mph above the posted speed limits, then you can safely put an S (rated for 112 mph) tire on the Corvette or Porsche. You'll still be able to run the Corvette or Porsche up to 112 mph for short periods of time. You'll even be able to run the car at 112 mph for sustained periods of time, because the tire is built to withstand 112 mph for sustained periods of time. And if the tire is built to go 112 mph for sustained periods of time there is obviously a safety factor built in and its good for a higher speed than that for at least short periods of time. Now, reasonably speaking, who among us is going to drive two lane highways and freeways at more than 95 mph for sustained periods of time? Or 105 mph for sustained periods of time, which is still 12 mph under the S tire's 112 mph sustained speed safety rating? Not to mention that you'll be breaking the law, may get an enormous ticket, and may not be a good enough driver to drive 112 mph for sustained periods of time. A tire's speed rating takes into account speed during cornering. Obviously, the tire's not always going to be going in a straight line, and will be subjected to cornering. So the cornering ability of a car at speed does not determine the tire rating. Its false to say that a Porsche will take corners faster or quicker than, for example, a Subaru Forester, so a Porsche needs a higher speed rated tire than a Forester. As far as cornering goes, the Porsche only needs tires with a speed rating equal to the top speed at which the Porsche will in fact be cornered. So if you aren't going to be driving down the road at over 95, or 105, mph (or indeed, 112 mph), the S tire, rated at 112 mph, is again more than adequate on the Porsche. As a matter of fact, if you corner the Porsche tight enough and fast enough you'll either roll it or spin out long before you hit over 112 mph. The higher the speed rating, the more expensive the tire, because the tire must be built better to withstand the higher speed. The higher the speed rating the harder (as against softer) the ride, because of the sturdier build of the tire. So those who buy tires with a speed rating way above the speed at which they'll drive are wasting their money and sacrificing softness of ride. My state has no law requiring a tire to match the vehicle manufacturer's speed rating or the speed rating of the tires that the vehicle came stock with. If your state does, I'd like to see an official citation to that law or a post with the law reproduced in the post, because I strongly suspect that claims of laws governing this are based on myth or are untrue hearsay. As to liability issues and fears of insurance company claims, since the speed a tire's run at, not the vehicle's top speed, determines the tire's speed rating, most of the claimed concerns over such things as lawsuits and insurance company denials are bogus, so long as you were driving at or under the tire's speed rating. I know, I'm a lawyer. If you had a tire-related accident while driving your Porsche at 100 mph with a 112 mph rated S tire you were well within the tire's speed rating and the fact that the Porsche would do 160 or more at top speed is irrelevant. In fact, if you were going 100 mph in the U.S. with an S speed rated tire, your speed and recklessness are what's going to get you into trouble with the lawyers and the insurance companies, not the speed rating of your S rated 112 mph tires. In addition, we all know that an insurance company often uses any excuse to refuse to pay and you can't do anything anymore without someone saying that it will subject you to a liability lawsuit. Who of us lets the constantly asserted and largely groundless threat of liability suits determine all aspects of our life? If a manufacturer recommends a particular tire speed rating its probably because the car is capable of a sustained speed equal to that speed rating. Yes, they are probably trying to cover themselves, because they know that many people will drive at the 120, or 140, or 160 mph that the car's capable of and may do so with tires that aren't rated for that speed. But if that happens, the manufacturer is not going to be liable. It wasn't the car's fault. It was the fault of the driver who drove above the tire's speed rating. There is nothing that requires you to run tires equal to the manufacturer's recommended speed rating. Doing so when you won't be going that fast costs you money and ride softness and plays into the hands of manufacturers who are trying to use you and your money to insullate themselves from their fear of groundless lawsuits. Speed ratings were first developed as a response to the fact that people were driving Germany's autobahn's at very high rates of speed -- 120, 140, and more, mph. The speed ratings let people know that they could buy tires that were safe for sustained driving at a particular high speed. If a person never drives the autobahn at, say, more than 112 mph, then they are ok with an S rated tire, even in a Porsche, and they are also ok with that tire if they don't drive faster than 112 mph on the U.S. highways. A higher rated tire is overkill on American roads for those of us who drive at sustained speeds at or below the speed limit or even no more than 10-20 mph over the speed limit.
If I were a lawyer, I think it would be easy to argue that an S rated tire used where a V rated tire is specified would constitute negligence on the part of the tire shop: 1) The vehicle manufacturer does all its testing with a V rated tire, and the tire shop probably didn't do any testing at all - especially on the vehicle in question. Put another way, the tire shop did not use reasonable care when installing a speed rating lower than what the vehicle manufacturer specified. 2) Along with speed capability, a higher speed rated tire commonly has increased grip and cornering crispness, so the vehicle brakes quicker and reacts quicker to steering input. But as an engineer, I also know that the test used to rate the speed capability of a tire has a given set of conditions and that using other conditions can result in lower speed capability. For example, using lower inflation pressures can result in lower speed capability. Also, the rubber degrades over time (and usage). So a tire's rating is only good when the tire is new. When it comes to specifying a tire speed rating for a vehicle, a lot of engineering consideration is given, some that isn't in the published literature. For one, it is common engineering practice to overdesign and underutilize. This practice is used because even with the sophisticated analysis available and the high speed computers commonly availbe, and engineer still can't know (or describe) all the possibilities that can occur. This is one of the lessons that was learned as a result of the Firesone/Ford situation a few years back. As a direct consequence, vehicle manufacturers are using tires that have more load capacity and more speed capability to reduce the probability that something unforseen will result in a vehicle accident. It is just good common sense to use the speed rating as specified.
I agree with capri racer. Although, technically, the speed rating only gives the maximum speed the tire can safely maintain, there's a lot more that goes along with that. There are definitely some exceptions, but most of the time a higher speed rating means you can expect the tire to be more stable at a given speed. This isn't necessarily true when comparing close speed ratings (ie: H vs. V) between manufacturers, but a name brand Z rated tire will almost always be stiffer than an H or V rated tire (a couple exceptions are R compound tires and Azenis which are often H or V rated). Just to go along with the above example, there are plenty of H and V rated tires out there that ride comfortably, but I can't think of an S rated tire that'd be stable enough that I'd want it on my car.
Originally posted by Nick29: (ie: H vs. V) between manufacturers, but a name brand Z rated tire will almost always be stiffer than an H or V rated tire (a couple exceptions are R compound tires and Azenis which are often H or V rated). Just to go along with the above example, there are plenty of H and V rated tires out there that ride comfortably, but I can't think of an S rated tire that'd be stable enough that I'd want it on my car.
Funny you bring up the Falkens as an example, since they are all over the map. I put their Ziex 512 (V rated) on my car and they rode like a bloated 1970s 80 series S tire. Whatever stiffenss Falken built into the Azenis they saved on the Ziex.
That's because the Azenis is an ultra high performance summer tire (it's basically an R compound carcass with a streetable rubber compound/tread design) and the 512 is an all season performance tire. You might as well compare Bridgestone's RE92 to the SO3. They're different tires, made with different uses in mind, so it makes sense that they'd be. . . different.
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