The "Big Deal" About Tires - Part 1
March 16, 2009
As we continuously listen to all the talk and confusion about "tire testing," "good tires," "bad tires," etc, I hope to clear up some of the confusion as to what the “big deal” about tires really is. When we go to a tire store, most of us will simply have a set of tires thrown on and drive away. Unfortunately in NASCAR, it isn't quite that simple. Also bear in mind, every time a driver pulls into the pits for a set of 4 tires, the owner just spent $1,600.
There are many different types of tires available, both commercially and in NASCAR. Not an infinite number, but a number that is large enough to stagger the imagination. With the inflow of synthetic type rubbers and various compositions of natural and synthetic rubber, the number is limited only by the engineer's imagination. While Good-Year & NASCAR won't reveal the actual composition, we can still look at the general guidelines used in the manufacturing and selection process for the racing tires.
The first factor is the "tire hardness." A device called a “durometer” measures the hardness of a tire. This machine measures not only the hardness of tires & rubber, but also plastics, metals and any other material in which the hardness or temper may be a factor. Rubber (including automotive tires) and soft plastics are measured in a scale known as "Shore A", which is just one of 12 scales that are used in determining material hardness. The scales range from 0 to 100 durometer, 0 being the softest. Most tires range between 55-70 durometer, whereas a rubber band will measure 20-35.
In addition to the hardness of the tires, the tire composition is also a determining factor as to which tires Good-Year will choose to bring to a track. As mentioned, there are many types of rubber and synthetic (man-made) blends as well as different amounts of carbon used in the tire surface and overall construction. Some of the more common types of rubber are Buna-N, Viton, Neoprene, & Latex. The Good-Year engineers will analyze the tracks, projected temperature & conditions and manufacture the tires based on previous successes & performance issues.
How might these factors apply?
First, the track surface must be determined. What is the balance of concrete to asphalt? What surface is in the turns? What surface is used coming out of the turns when grip is needed for quick acceleration? Most of the emphasis is placed on the turns because this produces the greatest amount of wear. If the turns and exits off the turns are concrete, a softer tire will be used because concrete has a smoother surface. This allows softer tires to grip better and the track surface will not cause extensive wear. If a track is predominately asphalt, a harder tire will be used because it will better resist wear. Since asphalt is a rougher surface, grip is not a major concern so a harder tire will be used because it will last longer.
Secondly, the track type must be determined - short track, long track, superspeedway, road course, etc. In other words, how much braking will the driver do? Short tracks like Bristol & Martinsville or a long tracks like Pocono & Indianapolis, where the driver will use a lot of brake pressure going into the turns, will produce large amounts of heat on the brake rotors and that heat is picked up on the tires, in particular, the bead (area that attached to the tire rim) and the inside sidewall. This becomes more evident when the networks install an axle camera to show the heat of the brake rotor. Long tracks like Daytona and Talladega where breaking in minimal will produce a lesser amount of heat on the brake rotors.
Thirdly, everything has a trade-off. In other words, a tire that resists heat may not wear as well as a tire that does not resist heat. Or a tire that is used for asphalt may have trouble withstanding the heat. Good-Year must produce the best overall balanced tire for the race, and as we have seen in many past races, they don't always get it right.
In Part 2, we'll look at the car set-up and how it determines the tire wearability.
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