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Understanding your car's tires



Understanding your car's tires

The saying, "Where the Rubber Meets the Road" has never been more important than it is with today's modern automobiles, SUV's and trucks. Understanding your car's tires can help you be a safe driver and get lower auto insurance rates.

The entire method of control, safety, comfort, and performance of your vehicle comes from a small, roughly five inch square imprint on which each of your tire's makes contact with the road.

No matter how fast, luxurious, complex, powerful, and sophisticated your vehicle is. Along with your cars suspension system and shock absorbers, literally everything that allows your car to drive smoothly and safely is through your tires and their contact with the highway.

Tires carry you, your children, your spouse, friends, and family - all the special people in your life. If your tires are old, weather cracked and worn out, with little or no tread, then you are taking a huge risk of a blowout, accident, or worse.

If you are buying tires, like most of us, you will rely on a reputable tire dealer to install the best tires for your vehicle.

Let's learn about what is on a tire sidewall so we can know more about what we are buying.

Assume for a moment you are looking at the tire sidewall of a typical American made sedan. For demonstration purposes let's take a look at the tires on a Ford Taurus 4 door sedan that are marked P225/60R16 98T.

Tire Size Markings

The tire size on this vehicle is expressed on the sidewall as P225/60R16 98T:


  • The P represents the car type, which is P for Passenger.
  • The 225 represents its section width (tire width in mm).
  • The 60 is the tires Aspect Ratio (the ratio of the sidewall height to the tread width). Some tires have a very low profile for performance and others are higher to give greater cushion and soften the ride.
  • The R represents radial tire construction, (as opposed to bias construction). Almost all modern passenger car tires today are radial construction.
  • The 16 represents the rim/wheel size expressed in inches.
  • The 98 stands for the load index. The load index number tells us the tire on this vehicle is able to carry a maximum load of 1,663 lbs per tire, (750 kg).
  • The T represents the speed symbol which gives the speed rating of the tire.

Since it cannot be assumed a driver will always observe the speed limit, tires are rated for high speed durability by very strict controlled testing. The tires on this vehicle, with at T rating, can be driven at a maximum continuous speed of 118 miles per hour, (190 kph). Not that you should do that, but tires must be built with excess capacity in order perform efficiently and last as long as possible.

Recently the speed rating has begun to be referred to as the "performance rating" of the tire, since the higher speed rated tires generally offer improved handling and maneuverability compared to lower speed rated tires. The speed symbols range from A to Z and each have a different speed category (top speed). Here is the speed chart for the most common passenger car tires:

  • S 112 mph (180 km/h)
  • T 118 mph (190 km/h)
  • U 124 mph (200 km/h)
  • H 130 mph (210 km/h)
  • V 149 mph (240 km/h)
  • W 168 mph (270 km/h)
  • Y 186 mph (300 km/h)
  • Z Above 186 mph (above 300 km/h)

A spare tire may be rated an M or N while many of the ratings between N through R are for light trucks. And it is not a typo; H is at the bottom of the speed chart between U and V for some reason unknown to us.

Going back to the load index number we'd like to note that the higher the tire's load index number, the greater its load carrying capacity. Typically, the load indexes of the tires used on passenger cars and light trucks range from 70 to 110. A 71 can carry only 761 pounds while one rated 110 can carry 2337 pounds.

Other information on a typical tire sidewall would be information such as maximum cold tire inflation pressure, tread wear, traction, and operating temperature ratings, and tire ply construction, and US DOT (Department of Transportation) safety codes.

Also remember that as tires wear and get older on the vehicle, their load and speed ratings would tend to be less than they were when brand new. Your tire dealer has tables available which will give you the load index, ply ratings and load range of different tires and can explain how will determine the right tire for your vehicle's needs.

As you can see tires are complex, but the tire industry has standardized the system which will allow the average person buying tires to have a fairly good idea of what he or she is getting.

Remember to buy the very best tires you can afford; keep them rotated and balanced for the longest wear and good ride characteristics.

There are no tire discounts on insurance policies, but other safety devices can help you with discounts. For example, anti-locking brake systems will help reduce your premiums. CarInsurance.com Insurance Companies do reward safe drivers with a reduction of premiums. Your primary goal is to avoid causing injury to yourself or others and to save money by avoiding expensive auto insurance claims. Good tires help you and your family to drive safely and achieve the least possible expense for auto insurance.


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