The tire shown above is a 205/45/ZR17 88w. 205 is the width of the tire in millimeters. The next number is the aspect ratio. In this case 45 represents that the side of the tire is equal 45 % of the width. 205mm x .45 = 92.25mm, or about 3.63 inches. A popular misconception is that sports cars have lower profile tires than what is used by Volvo. In many cases this is not true. Take a Corvette for example. The common tire size is 275/40/ZR17. The aspect ratio is lower but the tire is also much wider. 275mm x .40 = 110mm or about 4.33 inches. This is a full 7/10's more sidewall. The next number on a tire sidewall is proceeded by two letters. The first of the letters will be the speed rating, explained later. The second, usually R, represents that the tire is radial. The following number is the rims diameter. The final number is the load rating. In this case 88w.

        Here the tire properties can be seen. Treadwear circled in blue is how long you can expect the tire to last. The old axiom is to multiply the number by 100 to get the estimated tire life. In this case 140 x 100 = 14,000 or about 14,000 miles (22531 km) of tread life. Next comes traction and temperature. "A" represents the best "B" the next best and so on.

Circled above is the wear indicator. When the tread has reached this point you need to replace the tires.

Speed Rating

Q Up to 100mph

S Up to 112mph

T Up to 118mph

U Up to 124mph

H Up to 130mph

V Up to 149mph

W Up to 168mph

Y Up to 186mph

Z 149mph and over

Tire Maintenance

         Now that you know a little about your tires, you need to know how to take care of them. Rotation and balance is one important factor. This is something that should be performed by your dealer. For best tire life, rotate them every 5,000 miles. As for balancing that is only required as needed.

         Now, how do you properly inflate your tires? There are a few common mistakes. Some people think that they can inflate the tires to the maximum recommended pressure. In the case of the tire above, that would be 50 psi or 4.14 bars. Not only would this shorten the tire life and performance capabilities, but it would also produce a very uncomfortable ride. The dealer recommended pressure for most Volvos falls between 30 and 40 psi. Slightly more can be used on low profile tires to prevent rim damage. Ok, so lets say you decide to go with 35 psi for your Volvo to start with. All you need to do now is jump in your Volvo drive to the gas station right? Not quite. You should have 35 psi when the tires are cold. Why does this matter? I have prepared the graph below to help illustrate this point.

Tip: If you must fill up at a gas station, slightly overfill the tires and adjust them the following morning before you drive the car.

These simple things will help keep your tires on the road and safe longer.