ALT-1 How to Buy Racing Tires
If you want to buy racing tires for your car, the first thing you must decide is what kind of racing are you going to be doing. The second question would have to be, are you going to be using the car on the street as well. A lot of dedicated racing tires lack the DOT stamp of approval, and are not legal for use on the highways and byways of America.
If you want to go drag racing with your new tires, your choices are treaded tires or non-treaded tires. For the treaded tires your choices are radial tires or bias ply tires. Bias ply tires have been manufactured for over 100 years and the vast majority of racing tires are bias ply tires. In the bias ply realm you have tires like the Mickey Thompson ET Street's, which are basically a drag racing slick with 3 longitudinal grooves in them and the DOT seal of approval.
The ET Street's size designations are different than a radial tires markings. The ET Street's are marked with the actual size in inches on the sidewalls. This makes it easier to fit the tire to your particular car. A tire size is designated like this 28 x 12.50-15, which means the overall height of the tire is 28", the section width (overall from sidewall to sidewall) is 12.5", and it fits a 15" rim. They are available in a M5 compound which is a medium soft compound, good for most purposes.
Radial tire measurements are a little tougher to decipher, as they are given in millimeters. They are also listed by tread width not section width, so fitting the proper size to your car is a little trickier as well. A drag radial tire size would be listed as 275/60R15, which translates to 275/25.4 = 10.83" tread width. The 60 is the tires "Aspect Ratio", which is the ratio of the tires sidewall height, from rim to tread versus the tread width. In the example 10.83" x .60 = 6.5", 6.5" x 2 sidewalls = 13" + 15" rim size = 28" overall height. The "R" stands for radial construction tire. So in English this tire is 10.83" x 28"-15", keep in mind the overall width of the tire is larger than this, when fitting them to your car.
If carving corners is more your style, you'll need to purchase road racing tires. Road racing tires are made in both radial and bias ply construction, their sizes are given in inches. Road racing tires are made in treaded and slick configurations, and available in various rubber compounds. Road racing tires are usually made with a very low aspect ratio (short sidewalls), which are stiffer for better cornering performance.
The other numbers given on the tires sidewalls are: temperature rating, "A" being the best rating. Traction rating, again "A" is the best rating, and the tires speed rating, which is the maximum safe speed for "continuous use". Speed ratings are as follows:
S - 112 MPH / 180 KPH
T - 118 MPH / 190 KPH
U - 124 MPH / 200 KPH
H - 130 MPH / 210 KPH
V - 149 MPH / 240 KPH
Z - 149+ MPH / 240+ KPH When these were first introduced it was thought that this would be the highest rating ever required. Since then with new cars being made that are much faster than this, new ratings have emerged. Which explains why the "W" & "Y" ratings are faster than the "Z" rating.
W - 168 MPH / 270 KPH
Y - 186 MPH / 300 KPH
One last thing to keep in mind if you are using racing tires is, the reduced tread depth and softer rubber compound means that they wear out very quickly, and wet road performance is less than stellar. Race tires are actually made in a wet tire configuration because of this fact.
