T Rated Tire Instead Of Homework

Most modern passenger tires bear a tire speed rating, a designation indicating the tire’s designed speed capability. In other words, it’s the fastest speed a tire can handle before it does not perform as designed. Tire speed ratings do not imply that the vehicle may safely be driven at the maximum speed for which the tire is capable, particularly under adverse weather or road conditions.

How to Find Your Tire Speed Rating

If you’re wondering what tire speed rating your vehicle manufacturer recommends, simply look in the manual. You might also find it in the driver’s side door jamb, the gas tank hatch, or inside the glove box door – anywhere that lists the right tire code for your vehicle.

Speed rating is easy to locate because it’s usually the last item in the character sequence in the tire’s size code. For example in this tire code: “P205/60R16 82S,” S is the speed rating. To view the tire size code for your current tires, just look at the sidewall. Does the speed rating on each tire match what the manufacturer recommends? It should!

Also remember that the tire speed rating isn’t the same thing as a recommended travel speed. The rating will nearly always exceed maximum highway speed limits, but no tire or vehicle manufacturer advises driving faster than the law allows.

Determining Tire Speed Rating

Speed ratings are the product of laboratory testing – with simulated speeds and loads. To receive any kind of rating, a tire must demonstrate that it’s capable of sustaining a particular speed. Industry standards govern the process of reaching and maintaining a given speed during a test.

However, it’s important to remember that the lab can’t simulate every conceivable condition. Think of your tire’s speed rating as an indicator of the product’s capability under controlled conditions (i.e. fully inflated, vehicle running properly, good weather conditions). Your tires’ actual speed capability may be less than its rated speed, since it is affected by factors such as inflation, wear, vehicle condition (including alignment), driving conditions and the duration at which speed is maintained. Speed ratings do not apply to tires that have been damaged, altered, under-inflated, overloaded or repaired.

Tire Speed Rating System Quirks and Anomalies

Today’s speed rating system uses letters A through Z. Each letter corresponds to a specific speed. In general, that speed goes up as the rating advances alphabetically. For example, a tire rated “L” is good for a lower maximum sustained speed than one rated “N.”

But the tire speed rating system isn’t without its quirks. For instance, the system’s European roots give it unusual mile per hour maximums. Another such quirk is that the letter “H” is out of place. Instead of appearing after “G,” it falls between “U” and “V” as does the speed to which it corresponds.

Additional speed rating “anomalies” include the following:

  • “I,” “O,” and “X” speed ratings don’t exist. Likewise, some speed rating charts don’t include the “P” rating.
  • Tires with the lowest speed ratings are usually listed as “A” followed by a number– for example, “A1,” “A2, “A3,” and so on.
  • Some tires carry “W” or “Y” speed ratings. Manufacturers may also insert “Z” into the size description (in the tire code data between aspect ratio and diameter) for these kinds of tires.

When the speed rating system was first developed, the highest speed rating was the unlimited “V” rating. This was for tires whose maximum sustained speed was 149 mph (240 kph) or more. Then, as more manufacturers came out with tires that could handle speeds in excess of 149 mph but still hit a maximum speed at some point, “V” became limited (149 mph instead of 149+ mph) and “W” and “Y” speed ratings were added to the chart.

Many tire speed rating charts also list the “Z” rating as anything over 149 mph. Some manufacturers will insert a “Z” in the middle of the tire size description (right after the aspect ratio) when the tire is rated at “W” or “Y.” And if a tire is rated in excess of 186 mph (300 kph), manufacturer’s usually will list a “Z” within the size description, per industry standards.

Common Tire Speed Ratings Chart

The following speed ratings are those you’re most likely to encounter for ordinary vehicles. They begin with a maximum speed of 118 mph (190 kph) and increase from there.

Indicated by a letter, each rating corresponds to a specific speed.

Speed Rating T

With a maximum speed of 118 mph, you usually find tires with speed rating “T” on family sedans and minivans.

Speed Rating H

If you recall from earlier, the “H” speed rating doesn’t appear after “G” but between “U” and “V.” It represents a maximum speed of 130 mph (210 kph) and is commonly found on sports sedans and coupes. In earlier incarnations of the speed rating system, “H” stood for “high performance,” which is why it maintains an unusual position in the speed rating spectrum today.

Speed Rating V

Once the highest speed rating a tire could have, “V” used to represent a maximum of 149 mph (240 kph) or more. Nowadays, it means 149 mph but no higher.

Speed Rating W

A relatively new addition to the speed rating chart, tires with speed rating “W” can achieve a maximum sustained speed of 168 mph (270 kph).

Speed Rating Z

A “Z” rating can mean different things. While it nearly always means a high performance tire for high-performing sports cars, “Z” may actually appear in the middle of a tire’s size information. When it does, it represents either a maximum speed of more than 149 mph (240 kph) or 186 mph (300 kph). Which of those speeds it refers to will depend on the specific tire. Contact the manufacturer to get details on any Z-rated tires. Sports car owners are more likely to encounter this speed rating than owners of typical family sedans.

Always choose the speed rating that corresponds to your vehicle manufacturer’s specifications, and be sure all four tires have the same rating. Speed ratings are based on laboratory tests under specific, controlled conditions. While these tests relate to performance on the road under those conditions, remember that real-life driving is rarely identical to test conditions.

There seems to be a misconception that is very common on the web.

“I’m not going to drive 1** mph so there is no reason I can’t downgrade my tires” .

Part of the attraction here is to purchase a cheaper, longer lasting, lower rated tire…but at what risk?

Vehicle Manufacturers:

When cars are manufactured, they are tested with the size, load and speed-rated tire eventually assigned to the car. The suspension and engine options also effect the recommendations for specific vehicles. Tires with different speed and load ratings handle differently. Maneuvering corners and general handling of the vehicle can be compromised by downgrading the speed or load ratings of the tires assigned to the vehicle. Cars that have higher speed ratings have different performance criteria. Many import manufacturers have tires with higher speed ratings assigned to their vehicles for performance reasons.

Tire Manufacturers:

Tire speed ratings are assigned to tires based on a series of test conditions. These ratings are derived from optimal conditions and near perfect temperature and safety situations. FYI, speed ratings may not apply to a repaired light truck or passenger car tire and don’t reflect the performance of a compromised tire.

From the Michelin Website:

Speed Ratings Refer to More Than Just Speed

Speed ratings make a difference not only in regards to speed, but in regards to ride comfort, wear and cornering ability. Typically, the higher the speed rating, the better the grip and stopping power, but the lower the tread life. You can always increase the speed rating of the tires on your vehicle for improved performance, but can never decrease it without reducing the vehicle top speed to that of the lower speed rating selected.

Mixing Speed Ratings

If tires of different speed ratings are mounted on a vehicle, the lower speed-rated tires should be placed on the front axle regardless of which axle is driven. This is to prevent a potential over steer condition. Vehicle handling may be affected, and the vehicle’s speed capacity is now limited to the lowest speed-rated tire. For best performance, it is recommended that the same size and type of tire be used on all four wheel positions.

From Rubber Manufacturers Association:

“Always check and follow the recommendations in the vehicle owners manual and/or the vehicle tire placard regarding the use of speed rated tires. In general, all tires on the vehicle should be the same speed rating and replacement tires should have a speed rating equal to or greater than the speed rating of the OE tires.”

“Tires with different speed ratings may vary in ride, handling and/or other performance characteristics. Thus, care should be taken when mixing tires of different ratings on the same vehicle. It is the “top speed” of the “slowest” tire on the vehicle which limits the vehicles top speed without tire failure.”

“Consult he Vehicle Owners Manual or tire placard for the correct size and speed rating of the original tires. To avoid reducing the speed capability of the vehicle, replace a speed rated tire only with another tire having at least the same speed rating.”

“If tires of the different speed ratings are mixed on the same vehicle, remember that the tires may vary in ride, handling or other performance characteristics. Thus care should be taken when mixing tires of different speed ratings on the same vehicle.”

Bottom Line:

At this point there does not appear to be any state or federal law that requires the use of vehicle manufacturers recommendations when replacing tires. However, downgrading the speed rating of your tires may affect the handling and safety of your vehicle and may also leave you and the installer legally vulnerable. Trial lawyers have discovered they can get big money in tire lawsuits. There are some tire retailers that will be willing to downgrade your recommended tire rating to make the sale. However many reputable tire dealers and installers may not be willing to do this for you for liability reasons. At Brown’s Alignment we will prefer to err on the side on caution with respect to any safety concerns related to your vehicle. We recommend that you replace your tires with the size and rating that the manufacturer concluded was the best choice for your particular car. Suggestions that tire dealers prefer to sell the higher priced tires for ulterior motives, such as to make more money are not always the case. Our profit margins at Brown’s Alignment are lower on the upper end, more competitive tires.

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