Tire Speed Rating and Why It Matters
One of the most important aspects of any tire is its speed rating. The wrong tires with a less-than-adequate speed rating for your vehicle can cause safety issues, including tire failure and a loss in fuel efficiency. Let’s take a look at speed ratings, where to find the right one for your car or truck, and why it should always match the needs of your vehicle.
What Is the Speed Rating on a Tire?
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 speed rating sits alongside the load index on the side of every tire. Also called the performance rating, the letter (or letter/number combination) rates the tire’s performance in dissipating heat, cornering, braking, and steering. The letter in a speed rating represents a maximum speed based on a standard chart (seen below).
Tire Speed Rating Chart
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.
Speed Ratings 101
Generally, the higher in the alphabet a tire is rated, the better it will manage heat and faster speeds.
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 affect 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 safely 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 and some electric vehicles). Most winter tires have Q, S or T speed ratings.
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 capabilities, such as proper tire inflation, wheel and tire balance, vehicle alignment, tire tread, weather, and other conditions.
Don’t use the rating as a guideline for the top speed you can drive. If you’re carrying a heavy load or your tire is low on air, your tire’s speed capacity will be reduced. For safe driving, keep your speed at the posted speed limit — or below, when road conditions or the weather aren’t ideal. After a tire puncture has been repaired, keep in mind that some manufacturers suggest a tire’s speed rating may be reduced.
Where Do I Find My Tire’s Speed Rating?
From left to right on the sidewall of your tire, you’ll likely find the tire class (indicated with a letter), the section width (number), aspect ratio (number), the tire construction (letter), the tire’s load index (a two to three-digit number that corresponds to the weight each tire can support), followed by the speed rating. You can also find the speed rating in your vehicle owner’s manual, on a sticker in the driver’s side door, or stop by Les Schwab and we’ll look it up.
How Are Speed Ratings Determined?
Tire manufacturers determine a tire’s capacity for heat and speed using a testing machine. Testing is done to meet ECE (Economic Commission for Europe) standards, with a scale based on kilometers per hour (km/h). A more rigorous test is sometimes done to meet SAE (Society of Automotive Engineers) standards.
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 77º F. The tire is then pressed against a metal drum with enough pressure to simulate a realistic load.
Starting at a speed of 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. The tire spins for 10 minutes at the target speed. 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.
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. 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.
Does Tire Speed Rating Affect Your Driving and Tread Life?
Tires with higher speed ratings offer handling benefits, 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. However, there can be less ride comfort, lower performance in cold conditions, and shorter tread life.
What Tire Speed 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. Are you a “spirited” driver with a high-performance vehicle? You may be happier with V, W or Y tires. Light truck drivers should look 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 tires 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.
Les Schwab Is Your Tire Experts
The pros at your local Les Schwab can show you all of the options you need for work, weekends, or your daily commute. Add in our Best Tire Value Promise with unlimited flat repairs and free tire replacement and rotations, and you’ve found a partner who cares about service and your safety on the road.
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.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
- 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.
- 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.
- 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.
- 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.
- Get an alignment after you lower to ensure the best handling and tire life.
- 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.
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.
Can I Put Smaller Tires On My Car or Truck?
It’s common to see a lifted truck with bigger tires and wheels throughout the West. But what about going the other way? Is it okay to put smaller tires on your car or truck for a different look, when your original tire size isn’t readily available, or there is a chance to save some money? We have answers.
Smaller Tires Sometimes Make Sense
When replacing your tires, choosing tires that are within 3-percent of the diameter (the height of the tire) measurement of the tires recommended by the manufacturer can be acceptable if necessary. See our article on tire sizes and what the numbers mean. Those smaller tires, paired with a lowering kit, could enhance the looks of your vehicle.
Before making any recommendations, the pros at your local Les Schwab will double-check that the diameter, width, sidewall, circumference, load index, speed rating, and revolutions per mile match up with your cars or truck specifications.
Disadvantages of Significantly Smaller Tires
Choosing tires that are considerably smaller can cause extra wear to some parts of your vehicle as well as added costs when modifications are required. This could include a lowering kit, as well as new shocks. Depending on your goals, there are tradeoffs. Here are a few disadvantages to consider.
Interfering With Safety Equipment:
Tires that are significantly smaller than those suggested by the manufacturer can interfere with your speedometer, sensors and computers. These include safety systems such as anti lock brakes, emergency braking, and adaptive cruise control.
Overworking Your Engine:
Smaller tires can increase your overall torque, which can cause your engine to work harder as those tires spin faster.
Impacting Transmission Shift Points:
When tires are too small, the revolutions per mile are greatly affected, potentially changing when your transmission shifts. This can cause unnecessary wear and tear, leading to heavy-duty repair bills.
Les Schwab Tip: Changing tire size on an AWD vehicle may cause even more severe transmission issues. Check out our article about replacing all four tires on your AWD vehicle.
Reducing Tread Life:
Smaller tires will make contact with the road more often than those recommended by the manufacturer. The increased revolutions per mile of a smaller diameter tire means they will wear out faster and need to be replaced sooner.
Turning Heads (but Not in a Good Way):
Choosing smaller tires will change the look of your vehicle, but not always for the better, especially if you're looking for less expensive or more readily available tire options. Smaller tires may create a large gap between the top of the tire and the bottom of the wheel well, causing an unproportioned look on your stock-height car or truce. The only aesthetic fix is installing a lowering kit which has additional cost implications.
Looking at Larger Tires?:
Many of the same factors apply when considering a larger tire. However, those larger tires may be heavier than factory tires, causing added wear on shocks and struts. It may be in your best interest to upgrade your shocks and struts at the same time.
Why Would a Tire Shop Suggest I Get Smaller Tires?
At Les Schwab, we make sure to recommend tires that are well within the specifications for your ride. If you want to lower your vehicle or give your truck some height (lift), we have the experience to get it done right.
While some tire shops might do what they can just to sell a set of tires, we worry about your safety on the road. As long as a set of tires is within 3-percent of the diameter (height) measurement of the tires recommended by the manufacturer, you can feel good about the choice. Especially if it can save you some money when those tires are on sale or more readily in stock.
How Do I Tell What Size Tires I Need?
If you’re interested in switching out your tires for a different look, when your tire size isn’t available, or simply as a way of saving money, look for tire size information in your owner’s manual or on the placard located on the driver’s side door jam.
How Les Schwab Can Help
When you need the right size tires for your car, truck, SUV, CUV or EV, Les Schwab is ready to help. We’ll show you all of your options, mount and balance the ones you choose, and can align your vehicle if needed.