NASCAR Tech For Fans: Tires 101 with Patrick Reynolds

Former NASCAR team mechanic Patrick Reynolds (most recently with the Mike Wallace Nationwide series team) shares the inside story on just how much attention a racing team pays to tires. It’s a fascinating read for those of you who really like to dig down deep and learn the technical aspect of NASCAR. For the rest- it helps one appreciate a little bit more those finer details that figure into NASCAR success.

There are an infinite number of chassis set up combinations that any type of racecar can hit the track with. But with all the development in suspension science, a car only makes contact with a speedway on the four rubber patches the tire on each corner provides. They are extremely important in regards to racing performance.

In NASCAR’s upper leagues, the professional teams do not haul the wheels and tires with them to each venue like a local short tracker will. There is a trucking service provided for the Charlotte, N.C. area-based teams. The team wheels are transported to that week’s race site and the Goodyear workers mount the tires onto the wheels.

Upon arrival to that weekend’s garage area, each team’s tire specialist takes over. Every team had a designated member whose primary responsibility is to manage the tire and wheel inventory for the weekend. This job often monopolizes his time for the duration of an event. As long as tire work is caught up he helps in other areas, but first and foremost he is the “tire guy”.

The specialist will help unload his tire carts and tools and head over to the Goodyear trailer. This is the large eighteen-wheel tractor-trailer truck that fans will see parked in an infield’s garage area.

Tires are stacked in collections of four and lined up by car number. The specialist will haul his sets of tires to his own work area in the garage. Sometimes it will be near the rear of the team’s hauler. This location will vary from track to track depending on space available. There is a difference in elbowroom comparing Bristol to Talladega.

Data is then gathered from the tire’s sidewall and Goodyear sticker. Among the information attained are each tire’s manufactured date, serial number, circumference measurement, tread depth, and spring rate. Although the stacks of tires greet the tire specialist in groups of four, they are not necessarily the four that will stay together to put on a car.

Goodyear makes a left side compound and a right side compound, so a man will wind up with a selection of left side tires and a selection of rights. It is up to the team to put their inventory in sets for each corner. Spring rate is an important tool in this process.

The radial tires that slowly made their way into major league NASCAR racing in the early 90s, were accompanied with a spring rate. Each tire has its own rating and the tire specialist, crew chief, and engineer will move tires into sets largely based upon this number. They same way the actual springs in each corner of the suspension are chosen, tires chosen for each corner is similar to deciding on four additional springs.

Tires are also purged of the air that Goodyear has inflated them with. The atmospheric air that a compressor uses to fill a tire has high rates of hydrogen and oxygen molecules. These together make water, so when a tire gets hot on the racetrack, steam would form and expand in the tire.

Race teams fill all their tires with nitrogen. This will still build up pressure during green flag laps but not nearly as much as the air we all breathe. Nitrogen bottles also cost money, but it is a performance investment.

Each weekend Goodyear has a recommended pressure for the left and right side tires. Teams do sometimes vary from this for performance reasons. A basketball is a fair comparison. If the ball had two pounds of air pressure and it was bounced, the ball would not come back far off the ground. Now put fifty pounds in that same ball and bounce it. It will take off. Tires react similarly.

The inner liner pressure is increased to roughly fifteen to twenty pounds above the tire’s PSI. This holds the inner liner bead in place. If there would be a leak and both the tire and the inner liner wind up with the same pressure, they are said to be equalized. Remember the basketball comparison? A tire can feel like a dribbling ball on the racetrack when this occurs.

During practice runs pressure and tread temperature readings are taken. As we stated earlier the four tire patches are the only points the racecar contacts the track. They are full of information.

A hard working tire will be hotter than others. For example if a car is loose and the rear end wants to slide around, the right rear will be warmer than the front. If a car is pushing and doesn’t want to turn, the right front will be hotter than the rear. That is a basic explanation, but temperature is monitored across the tire surface in the inner edge, middle, and outer edge on all four wheels. Crewmembers look at the information and go about making changes to the set up. A pressure build will usually follow the temperature increase as well.

When a set of tires is removed from the car and a new set put on, tread depth is measured. Tire wear is also a very important piece of data for the team to digest. The depths on all the tires were measured when new, so a wear reading can now be made.

From practice runs, pressure build can now be anticipated to a degree. Teams know that over a long run the pressures will rise, which effects a car’s handling. So a starting point can be reasonably guessed when tires are tightened up and sent out to the track.

During qualifying, pressures are highly increased so they can have maximum performance in only a two lap run.

In the actual race, crew chiefs will use tire pressure adjustments as a tool for improving a car’s handling. This is where our spring rate comes back into play. Prior to radial tires being used, air pressure would be used to adjust the stagger. That is the difference in circumference between tires. Roll a drink cup on the ground and the larger end will always turn towards the smaller end. The rear tires formerly were used in the same manner. Radials brought an end to that.

Now the tire size doesn’t change with air pressure, but acts more like a spring. Air pressures can be raised and lowered but NASCAR and Goodyear do not want any team dipping below the minimum pressures they have established.

When pressure is adjusted, think of a softer or stiffer spring being put into action. In a case of a car being tight through the turns, one possible change would be to take a pound of air out of the front tires. This would soften the spring rate, give the front more bite, and allow the nose to turn better.

On a loose condition, the rear tires could be dropped by a pound, giving the car’s tail a better bite, and tightening a car up.

There are multiple combinations that can be used when adjusting tires. A single corner could be changed, right side pressures, left side pressures, or instead of dropping rear pressures maybe raising the front pressures.

These come from testing, gathered data, and experience with driver to crew chief communication on a team. Different drivers react differently to any changes in the racecar.

Being successful in professional motorsports is extremely difficult. There is quite a bit of information involved strictly with tires. Every tire specialist has a very busy job managing his team’s inventory. So much can affect a car’s speed here and we have not discussed anything mechanical on the car itself.

There is simply so much detail that goes into every aspect of racing. What fans may see as routine from the grandstands, might actually be a team member pushing himself to the limits so he doesn’t fall behind. A good “tire guy” lives this every weekend.

PHOTO CREDITS- Top left photo by Walter G. Arce, upper right photo by Total Photo (Leon), Pit area photo by Ozymandiasism. To see more of their work, click on the hyperlinks or visit flickr.com.