• Tire Speed Rating and Why It Matters

    The tire speed rating is the maximum speed tires can safely carry a load (the original weight of your vehicle plus whatever’s in it) for a sustained amount of time in ideal conditions. The rating is molded on the tire sidewall, signified by a letter or two, usually after the load index number. Together, the load index and speed rating form the service description.

    Each letter in the speed rating represents a maximum speed based on a standard chart.

    The main things to know:

    • Generally, the higher in the alphabet a tire is rated, the better it will manage heat and faster speeds. There’s an exception for the H rating; read on for why.
    • Your actual speed capacity may be less than a tire’s rating. The rating indicates a new tire’s performance in tightly controlled lab settings, not the open road. Tire condition, inflation level, extra cargo, road surfaces and weather are everyday limits that play into a tire’s maximum safe speed.
    • If you have tires with different speed ratings, the limit of the lowest rated tire is the fastest you can drive and stay within your tires’ capability.
    • The most common ratings are S and T (sedans, minivans, light trucks); H (some passenger cars, sports cars, coupes, some light trucks); N, P, Q and R (light trucks); and V, W and Y (high-performance cars). Most winter tires have Q, S or T speed ratings.

    Tire Speed Rating Chart

    Here are the symbols and translation into mph:

    SPEED RATING
      SPEED SYMBOL SPEED (mph)   SPEED SYMBOL SPEED (mph)   SPEED SYMBOL SPEED (mph)
      A1 3   E 43   S 112
      A2 6   F 50   T 118
      A3 9   G 56   U 124
      A4 12   J 62   H 130
      A5 16   K 68   V 149
      A6 19   L 75 ZR* W 168
      A7 22   M 81 Y 186
      A8 25   N 87 (Y) Above 186
      B 31   P 93 *For tires having a maximum speed capability above 149 mph, a ZR may appear in the size designation... above 186 mph, a ZR must appear in the size designation, including a Y speed symbol in brackets.
      C 37   Q 99
      D 40   R 106
      SPEED SYMBOL SPEED (mph)
      A1 3
      A2 6
      A3 9
      A4 12
      A5 16
      A6 19
      A7 22
      A8 25
      B 31
      C 37
      D 40
      E 43
      F 50
      G 56
      J 62
      K 68
      L 75
      M 81
      N 87
      P 93
      Q 99
      R 106
      S 112
      T 118
      U 124
      H 130
      V 149
    ZR* W 168
    Y 186
    (Y) Above 186

    *For tires having a maximum speed capability above 149 mph, a ZR may appear in the size designation... above 186 mph, a ZR must appear in the size designation, including a Y speed symbol in brackets.

    Note: Yes, the H rating is out of place and that’s not a typo. When tire speed ratings were first developed in Europe in the 1960s, there were only three ratings: S, H and V. As tire technology developed and new speed classes were introduced, the ratings table expanded to include the full alphabet. But the letter H kept its original speed rating of 130 mph, so it sits later in the chart.

    Z-rated tires will sometimes have the letters ZR embedded with the tire size information instead of in the service description.


    How are Speed Ratings Determined?

    Tire manufacturers determine a tire’s capacity for heat and speed using a testing machine. Usually testing is done to meet ECE (Economic Commission for Europe) standards, so the scale is based on kilometers per hour (km/h). A more rigorous test is sometimes done to meet SAE (Society of Automotive Engineers) standards.

    1. For the ECE test, the tire is properly inflated and mounted on a wheel attached to a testing machine in a room that’s heated to 77 degrees F.
    2. The tire is pressed against a metal drum with enough pressure to simulate a realistic load.
    3. Starting at a speed 40 km/h lower than the proposed rating level, the tire is spun for 10-minute increments at higher and higher speeds, until it reaches the target speed.
    4. The tire spins for 10 minutes at the target speed.
    5. It’s then removed from the machine and inspected for any failures, like separation of tread components. If it’s intact, it passes the speed rating.
    6. Sometimes an SUS (step-up speed) test will be added after the tire performs at the target speed rating. Speed is increased until the tire fails.
    7. If the tire is being tested at the SAE standard, it’s required to run for an hour at target speed in a room heated to 100 degrees.

    How Much Does It Matter for Your Driving & Tread Life?

    Tires with higher speed ratings offer handling benefits that thrill some drivers, but there are tradeoffs. Since they’re usually made with softer rubber compounds and stiffer construction they offer better cornering, stopping power and steering response. But expect a little less ride comfort, lower performance in cold conditions and shorter tread life. Consumer Reports found that some H- and V-rated tires didn’t last as long as those rated for lower speeds, wearing out closer to 50,000 miles than 60,000 miles.


    What Rating Do You Need?

    Even in states where rural speed limits are 75 mph, most drivers will stay well below the speed limitations of H-rated tires. Commuters and family car drivers will likely be quite satisfied with S or T tires.

    If you’re a spirited driver with a high-performance car, you may be happier with V, W or Y tires. Light truck drivers will be looking for symbols N, P, Q, R, S, T or H.

    If you’re replacing tires and think you may want a lower- or higher-speed-rated tire, it’s best not to mix and match. When mounting differently rated tires, techs prefer to put the lower-speed-rated ones on the front to prevent oversteering. This can conflict with the best practice of putting the tires with the most tread on the rear, which is important for wet traction.

    Get tires with the same speed rating. If you don’t, remember that the maximum mph is limited to the tire with the lowest speed rating.


    Key Takeaways

    Tire speed rating is not like a speed limit posted on highway signs. It’s based on lab simulations and doesn’t account for real-life factors that determine true tire capability: Are the tires fully inflated? Is your vehicle properly aligned? How hot is the road? Have you ever had a flat repaired? What’s the age and state of the tread?

    Don’t use the rating as a guideline for the top speed you can drive. If you’re carrying a heavy load, have a tire that’s been patched after a puncture, or low on air, your tire’s speed capacity will be much reduced. For safe driving, keep your speed at the posted speed limit — or below, when road conditions or the weather aren’t ideal.

    Important Notice: The information provided above is derived from sources deemed reasonably reliable. The operation of your vehicle, or the replacement of your vehicle’s equipment, may be different than for a typical vehicle. Please consult your owner’s manual for specific warnings, notices, and other advice relative to the subjects addressed.


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  • Lowering Suspension: Pros and Cons

    Lowering your car or truck so it’s closer to the ground is a popular way to customize your ride. Done right, it’s a great look that also boosts handling performance. Done wrong, it could compromise handling, drivability and traction, reduce tire tread life and even damage parts.

    Pluses and Minuses of Lowering Suspension

    PROS CONS
    More road feel Reduced ride comfort
    Stiffer ride Impractical for rough roads
    Less roll when cornering Accelerated or uneven tire wear
    Better handling Chance of bottoming out
    Improved aerodynamics Potential rubbing on parts or tires
    Improved traction Can’t use a standard jack
    Less rollover risk Cost
    Great looks Warranty issues

    Benefits

    More Road Feel
    A lowered suspension helps a driver be highly attuned to how their vehicle acts on different pavement as more of the vibrations from imperfections in the road surface come through the steering wheel.

    Stiffer Ride
    With this setup, you have to have more rigid springs so the front or back of your vehicle won’t bottom out over bumps or depressions. This is the driving experience many prefer, versus a cushier ride from, say, a luxury sedan.

    Less Lean in Corners
    The lean of a vehicle around a sharp turn is greatly reduced because the shift of weight is less due to the lower center of gravity. The part of the vehicle on the outside of a turn stays more level with the inside. This lets a car settle more quickly into a turn and act more responsively.

    Better Handling
    Another effect of being closer to the ground is improved responsiveness, more stability, and grip at speed. Because lowering means getting stiffer springs, there is less weight transfer when you hit the gas or brake hard. This means you’ll enjoy faster acceleration and quicker stops.

    Less Air Drag
    Lowered vehicles are more aerodynamic. There’s less air hitting the wheels and tires (that are not streamlined shapes). This makes these cars faster. Some owners of low-stance vehicles also notice improved gas mileage. BUT, lowering a car too much will actually increase wind drag.

    Less Rollover Risk
    Lowered vehicles have a lower center of gravity, which decreases rollover risk when cornering.

    Improved Traction
    Lowering generally means you’ll put a plus-sized tire and wheel package on the vehicle. Such tires have shorter sidewalls, a larger contact patch (that keeps more rubber in contact with the road) and less roll around corners.

    Good Looks
    Cars and trucks that have been lowered with custom wheels are attention-getters. It’s a more aggressive and performance-oriented look that stands out in a crowd.


    Drawbacks

    Less Ride Comfort
    If you and your passengers are accustomed to a softer suspension that cushions impacts like bumps and potholes, you may think less of the ride comfort of a lower suspension. You may also notice increased road noise since you’re closer to the pavement.

    No Go on Rough Roads
    The lower clearance will not be your friend on rutted, rocky, washboard and potholed roads.

    Uneven or Accelerated Tire Wear
    Lowering changes the geometry of your wheel-tire fitment. If it’s done improperly, your car may have an alignment problem that results in premature or extreme wear patterns.

    Bottoming Out
    Even an inch-and-a-half lower suspension can cause problems around corners, with slight potholes or on speed bumps. Traveling over the lip of a parking garage or starting up a driveway or ramp could cause the front of your vehicle to hit the pavement. Contact with the ground can cause serious damage to components underneath the car, like the exhaust system and oil pan.

    If you ever need a tow truck, you may require a flat bed. Otherwise, there could be a problem with the back body of the vehicle dragging on the ground.

    Potential Rubbing on Parts or Tires
    Poorly done or extreme lowering can cause suspension and steering parts to contact each other, the wheels or the tires. It could also cause tires to rub the body during turns or going over bumps.

    Can’t Use a Standard Jack
    If you get a flat tire, you may find out at an inconvenient time that there’s not enough clearance to get the unit under the vehicle’s frame.

    Cost
    Quality components and keeping correct alignment can get pricey. The lower you go, the more chance you’ll need additional parts. For example, if coilovers (meaning coil spring over shock) are part of your new setup, you’re likely looking at an outlay of $1,000 or more.

    Warranty Issues
    You should check both your owner’s manual and any manufacturer’s or aftermarket warranty to determine if 1) the manufacturer advises against lowering your car, or 2) if lowering your car will void or adversely affect any warranty coverage you currently have.


    Know This Before You Modify Your Suspension

    Here’s what to know before you go low.

    1. If it’s higher performance you’re after, you may need to lower a lot less than you think. It’s easy to miss the mark and actually make your suspension worse. To be sure that components like struts and springs can do the work of keeping tires at the right angles, get expert help.

    2. Don’t cut corners when it comes to shocks, struts or other components. You’re making changes to the structure and balance of your vehicle. You don’t want to risk failing parts.

    3. If you modify your vehicle in ways that aren’t road legal, your insurer may not pay a claim for damage. Talk to your agent before you customize your ride and ask if your premiums will go up or policy terms change.

    4. Installing extreme aftermarket wheel-tire setups or suspension changes can result in steering, suspension or drivetrain problems that won’t be covered by your vehicle warranty. Check to see if the modifications you’re planning will result in denied warranty claims BEFORE installation.

    5. Get an alignment after you lower to ensure the best handling and tire life.

    6. Take care while you get accustomed to how your new setup performs. With the much stiffer suspension, your vehicle may steer a little differently and won’t absorb road shocks as well. A sudden hard brake or tight turn on a bumpy road could cause a loss of traction.

     

    Any time you change your vehicle’s OE (original equipment) suspension, you should be sure that you’re not creating a setup that is either unsafe or is going to cause problems with other car functions. Like with many aftermarket customizations, it’s about finding the right balance of safety, performance, looks, cost, and drivability. Stop by your local Les Schwab for help.


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  • Run-Flat Tires: How They Work & What Sets Them Apart

    The space between your tires and the road can be a precarious place. Just one stray nail or screw can cause a flat tire and send you to the side of the road. Run-flat tires change all that, but there are trade-offs. Here’s what you need to know about run-flat tires, why some manufacturers are using them, and why you might or might not want to add them to your car or truck.


    What are Run-Flat Tires?

    First, let’s dispel the myth that run-flat tires never need air pressure. They do. The tires on your car or truck do not support the weight of your vehicle. The air pressure does that job. Run-flat technology works the same way with one big difference: the sidewalls on run-flats are reinforced (usually about ¾" thick as compared to 1/8" thick on standard tires) so that even if you experience a sudden and complete loss of air pressure, you’ll be able to drive on the tires for a short distance. Most run-flat tires can be driven on without air for up to 50 miles at up to 50 miles per hour.

    Standard vs Run-flat tire


    Why Were Run-Flat Tires Created

    If you’ve purchased a new car in the last few years, you may have noticed that many manufacturers have removed the spare tire. This is done to reduce weight, improve fuel efficiency, and provide more cargo space. But what happens if you get a flat? You’ll find that those carmakers may have given you an emergency tire repair kit or equipped the vehicle with run-flat tires.

    When it comes to convenience, run-flat tires are great. But the real reason they were invented was to improve the safety and steering response of high-end sports cars in case of tire failure. Over the decades since this technology was first introduced, run-flat tires have become more common on some high-end vehicles.


    The Benefits of Run-Flat Tires
    • Safety: More control in the event of a sudden loss of tire pressure.
    • Options: The ability to drive to your local repair shop after a flat.
    • Convenience: No need to carry a spare or change a tire on the side of the road.
    The Disadvantages of Run-Flat Tire Technology
    • Comfort: There can be diminished ride quality with the stiffer sidewall.
    • Noise: Some run-flat tires create more road noise inside the vehicle.
    • Repairs: While run-flat tires are repairable within warranty standards, driving without air beyond recommendations can make many repairs impossible.
    • Cost: Most run-flat tires come at a premium price.
    • Availability: Some specific sizes and tread options may not be readily available.

    How Run-Flats Compare to Standard Tires

    Both typically come with mileage warranties that cover the overall life of the tires with proper maintenance and care, and both come in all-season and other tread options. Additionally, both technologies fit onto standard wheels or rims. See our article Can I Mix Run-Flat Tires with Standard Ones for some added insight.


    Should You Install Run-Flat Tires?

    If your vehicle came standard with run-flat tires, you might consider it as a viable option — especially when your vehicle does not have a spare. If your vehicle did not come standard with run-flat tires, or if you’re unsure if you already have run-flat tires, stop by your local Les Schwab for advice. Depending on your vehicle and driving needs, our team can help you decide if run-flat technology is right for you.


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