pimped out cars

All about the numbers on Tires.

What are you buying when you look at tires. I think most people have no clue what is in a tire. What does the size of the tire mean? What do all those numbers and letters mean on the side of the tire? I think most tires are purchased base on name and advertising.

What is the sizing conventions? There are several sizing conventions. P Metric sizing, ISO Metric Sizing Alpha Numeric and Numeric.

People in the United States are most likely familiar with the P-Metric System. The others are older naming conventions. A typical tire which can be read on the wall of the tire would be P185/70HR13

P means Passenger Car. An LT Designation would be for Light Truck. The 185 is the width of the Tire in millimeters of the Car. The 70 is 70 percent. This is use to determine the distance of the tire wall from the Rim to the Tread of the tire. Therefore 70% times 185 equals 129.5mm. This number is know as the Aspect Ratio or the Ratio of the Tire. The letter H designate the maximum speed that the tire can be operated at. For “H” the Speed is 130mph. Sport Car tires as you may have heard use a Z or ZR rating which is a rating of 149mph. R denotes that the tire is a radial tire. 13 is the diameter of the Rim in this case 13 inches. I find it interesting that there is such a mixture of Metric and English units of measure system.

What does all this mean? If you are not going to excessively speed, buying a Z or ZR rated tire is an utter waste of money and also this tires typically use softer rubber and wear out much sooner.

Now the conversion to inches. 185mm is converted to 7.2 inches. 129.5 mm is converted to 5.1inches. Therefore the diameter of the wheel including the 13 inch rim is 18.1 inches and the width of the tire is 7.2 inches.

Now here is the interesting thing. My Pickup Truck has P not LTs on them.