The makeup of the sidewall is an important part of the construction of the tire because it defines how the tire will react as the car enters the corner. If the sidewall is made up of stiff rubber components, it will react in the turn like a tire that is over-inflated. It will respond to the steering input and be less affected by its grip to the track. If the sidewall is made up of softer rubber components, then it will react more like an under-inflated tire. It will respond less to steering input and be more compliant to the track surface. The car would feel less "sure" with a sidewall construction that is too soft.
The '04 tires laid out for...
The '04 tires laid out for Earnhardt Jr. at Homestead. All carry "D" embossed on the sidewall. The compounds will vary from side to side on ovals, and from front to rear on road courses.
The changes, as they relate to aero-dependent tracks, seem obvious to match the reduced aerodynamics to the tire compound. Tracks like Martinsville, Richmond, and Bristol seem less obvious to have new tires, but re-compounding and providing new constructions for these tracks follows NASCAR's and Goodyear's overall strategy to provide tires with "fall-off" and provide a more consistent "feel" throughout the tire's time on the car.
Fall-off of a tire is how the adhesion of the tire reduces as the tire gets more laps on it. A new tire will stick better than a tire with 40 laps on it. Consistent feel is very important for a driver. If the driver knows that the tire will loose adhesion slowly and predictably, he or she can use the maximum grip available from the car between pit stops. On the other hand, if the driver can't count on a consistent feel from the tires, he or she will have to drive more cautiously, trying to predict when the tires will change. This is not the fastest way around the track.
New Road Course Tires
Another important change for the '04 season is that the road course tires will be configured into the normal sports car mode. They will have separate front and rear tires. All four tires will be the same size, but the construction and compound will be different from the fronts to the rears. Different front and rear tires have never been seen in NASCAR racing. This is the most dramatic change in stock car tires since the change to radials. This should make for much more exciting road course racing by providing the drivers handling options never before possible. These options stem from a concept discussed earlier-the construction of the tires.
A rear tire on a road course as well as on ovals has a main job of getting as much power to the track without slipping. It does have a component in the cornering, but more important is getting power to the track. The front tires on a road course have the main job of pointing the car into the right and left turns. Until this year, sacrifices had to be made so that the same tire could do the job of a front or rear tire because the front and rear tires were of the same construction/compound.
The '04 tires laid out for...
The '04 tires laid out for Earnhardt Jr. at Homestead. All carry "D" embossed on the sidewall. The compounds will vary from side to side on ovals, and from front to rear on road courses.
The differences that the Goodyear engineers will place into the tires this year will not be hindered by these sacrifices. For example, to get the tires to transfer power to the track, a stiffer sidewall might be useful to keep the sidewalls from buckling under torsion load. At the same time, a slightly softer sidewall might allow the tires more grip as the car begins to enter the turn.
Date Codes Return
Another change was instituted at the end of the '03 season and will continue for all of the '04 season. Again, the date codes will be found on the tires. Date codes provide the date of manufacture for the individual tire. As rubber ages, it tends to harden. A good short-track example of this is beginning a new season with tires that were purchased in the previous season and allowed to sit during the off-season. A comparison of these tires to tires just pulled off the tire truck, in most cases, would show a durometer (grip) difference. If the older tires were combined in the same set as the new tires, they would not match up well. Cup teams, who must deal with minute changes throwing off a chassis setup, pay very close attention to the date codes. Goodyear will be providing this information as well as additional information to the teams.