Tire makers spend fortunes on laboratory tests to determine the speed ratings of high-performance tires, all the better for original equipment customers to assign them to new cars and light trucks based on those vehicles' top speeds.
But what if a tire dealer, faced with a customer who balks at the cost of an H-rated tire (top speed 130 mph), sells that person an S-rated tire (112 mph) instead? And what if that customer, deciding to push his car to the limit, has an accident?
Also, if a speed-rated tire is repaired, should the dealer tell the customer not to expect the original speed rating to hold good?
Sources contacted for this article said they know of no litigation against tire dealers or makers based on the issue of speed ratings. But some within the industry are wondering whether it's just a matter of time.
``We live in a sue-happy society where many don't want to take responsibility for our own unsafe action or behavior,'' wrote Bob Richey, owner-operator of Richey Inc./Goodyear Tire Center in Bellevue, Pa., and president of the Tire Dealers Association of Western Pennsylvania.
In a recent editorial in Tire Trax, the association's newsletter, Mr. Richey noted that it's far more important in a replacement tire to match the OE tire's tread design, tread width and construction than its speed rating. Dealers should consider the customer's driving habits, he said, but they should also consider his or her budget.
A lot of dealers who won't mix or reduce speed ratings on a car's tires will nevertheless pass vehicles in state safety inspections that have tires with mixed or reduced speed ratings, Mr. Richey said. ``This makes no sense at all!'' he added.
Nevertheless, Mr. Richey said he understood why some dealers are nervous about the speed rating question.
``This is a subject people are afraid to bring up because of fears of litigation,'' he said in a phone interview from his store. ``Vehicle inspections don't even address speed ratings, and they shouldn't because it's way overrated as a vehicle factor.
``We try to exercise good common sense,'' he continued. ``We talk to customers on how they drive and whether they need high-performance tires. We say a repair degrades a tire by a letter, though there's no way to look in there and see how the cords have been compromised.''
The Rubber Manufacturers Association (RMA) offers an eight-page pamphlet of guidelines on replacement tires available free for download from its Web site, www.rma.org.
In a box on the second page, the guidelines state: ``ALWAYS check the vehicle manufacturer's recommendations for the OE tire size, load capacity, inflation pressure and speed rating information before replacing a tire with a different size and construction. It is not always possible to select the same tire size for a replacement tire. NEVER choose a smaller size with less load-carrying capacity than the specified size on the vehicle tire placard.''
Trying to match speed ratings is a matter of the vehicle manufacturer's preference, not a safety edict from the National Highway Traffic Safety Administration (NHTSA), according to an RMA spokesman.
``In NHTSA safety testing, the top speed for testing any tire is 99 mph,'' the spokesman said. ``Their view is that no car should be going anywhere near 100 mph, so if you can go safely at 99 mph, that's enough for them.''
As a matter of course, it's good policy to adhere to the vehicle manufacturer's recommendations as much as possible in selecting a replacement tire, the RMA spokesman said.
``A driver might see the price on an H-rated tire and say, `It costs how much? I'm not going to drive 130 mph! Why does that matter?''' he said. ``It may not jump out at him that there might be other performance characteristics on a high-speed-rated tire that are desirable for his vehicle.''
As for the Tire Industry Association (TIA), its training programs state that the information on the vehicle tire placard-including tire size, load index and speed rating-be followed at all times.
``If the speed rating of the tires is less than the speed rating on the placard, the handling of the vehicle may be affected, which could lead to the loss of control,'' said Kevin Rohlwing, senior education and technical director at TIA. ``As far as we know, every state dealer and industry organization has the same recommendations for tire replacement.''
TIA recommends that dealers contact the tire manufacturers before trying to repair any speed-rated tire, Mr. Rohlwing said.
``If the tire manufacturer does not recognize the speed rating following a repair, can the dealer return the tire to service?'' he said. ``Technically, the answer is no. But explaining that to the customer who needs a simple puncture repair on a relatively new tire is almost impossible when every other dealer in town will repair the tire and bad mouth the dealer who tried to do it right.''
In its product brochures, Goodyear recommends replacing a speed-rated tire with a tire having an equivalent or greater speed rating.
``However, if you never drive at speeds near the limits of your speed-rated tires, you may choose to replace them with tires having a lesser top speed rating,'' the company states. ``In situations where tires having different top speed ratings are mixed on a vehicle, the maximum speed certification is limited to the top speed certification on the tire with the lowest speed rating.''
A Goodyear tire may keep its speed rating if it receives a nail hole puncture repair in the tread area using approved materials and procedures, the company said. Other repairs cause the tire to lose its speed rating, as does retreading.
Bridgestone/Firestone also recommends adhering to the vehicle manufacturer's recommended speed rating, according to Mark Kuykendall, a BFS engineer.
``The whole thing is that a vehicle is designed and developed with specific performance characteristics in mind,'' he said. ``When that car has the tires with the specified speed ratings, that's ideal.''
Customers often complain not only about the cost of speed-rated tires, but also their relatively short tread lives, Mr. Kuykendall noted. ``Often we'll hear, `This tire lasted only 25,000 miles!''' he said. ``The customers don't understand what a high-performance tire means.''
As for repairs of speed-rated tires, BFS's policy is simple. ``When a speed-rated tire is repaired, it loses its speed rating,'' Mr. Kuykendall said. ``It drops to the DOT non-speed-rated standard, which is 85 mph. In no way does it change the way the car handles. It just means you can't drive it at 130 mph.''
* * *
Speed ratings for tires are identified by means of a speed symbol (see following table) that indicates the speed category at which the tire can
carry a load corresponding to its load index under specified service conditions, according to the Rubber Manufacturers Association (RMA).
Although a tire may be speed rated, the RMA said it does not endorse the operation of any vehicle in an unsafe or unlawful manner. ``Furthermore, tire speed ratings do not imply that a vehicle can be safely driven at the maximum speed for which the tire is rated, particularly under adverse road and weather conditions or if the vehicle has unusual characteristics.''
Speed ratings are based on laboratory tests that relate to performance on the road, but are not applicable if tires are underinflated, overloaded, worn out, damaged or altered, the association advised.
Speed symbol: Speed category / Open-ended speed category
: *above 240 km/h (149 mph) / *ZR
Y: 300 km/h (186 mph) / *ZR
W: 270 km/h (168 mph) / *ZR
V: 240 km/h (149 mph) (with service description)
H: 210 km/h (130 mph)
U: 200 km/h (124 mph)
T: 190 km/h (118 mph)
S: 180 km/h (112 mph)
R: 170 km/h (106 mph)
Q: 160 km/h (99 mph)
P: 150 km/h (93 mph)
N: 140 km/h (87 mph)
M: 130 km/h (81 mph)
* For tires having a maximum speed capability above 240 km/h (149 mph), a ``ZR'' may appear in the size designation. For tires having a maximum speed capability above 300 km/h (186 mph), a ``ZR'' must appear in the size designation. Consult tire manufacturer for maximum speed when there is no service description. For example:
Tire designation: Maximum speed
P275/40R17 93W: 270 km/h (168 mph)
P275/40R17 93Y: 300 km/h (186 mph)
P275/40ZR17: Above 240 km/h (149 mph) (consult mfr.)
P275/40ZR17 93W: 270 km/h (168 mph)
P275/40ZR17 93Y: 300 km/h (186 mph)
LT235/85R16 114/111S: 180 km/h (112 mph)
(where 114 applies to the single load and 111 applies to the dual load)
NOTE: For ``V,'' ``W'' or ``Y''-and tires with a ``ZR'' rating-a vehicle load adjustment (for speed) is required; consult tire manufacturer.
Source: Rubber Manufacturers Association