Designate one or more people...
Designate one or more people to work with the tires. Never let an inexperienced person mount or air up the tires. For the sake of performance, have the tire person keep accurate notes on both cold and hot tire pressures, tire temperatures, and tire sizes. By using the same person, your tires will perform consistently week to week.
The tires used for racing have evolved from the best available production car tires years ago to specially built hybrids designed to perform under extreme racing conditions. Each company that produces and distributes stock car racing tires puts thousands of hours into research and development for a tire that will have good performance as well as durability to last the entire race or longer. To take advantage of all of that technology, racers need to know certain facts about preparing and racing tires.
Every team should have a designated tire person or two to select, air up, size, and maintain the tires. A tire program needs to be developed to ensure that the good setups will have a chance to show themselves by having the best tire tech. Based on the type of racing at a particular track, a team will eventually understand the value of knowing what the tires need, and then develop a routine to take care of them.
Tires are usually selected from a pile of tires at the racetrack. However, there are certain problems associated with this process. One inherent problem is the age of the tires. Older tires may have been mixed with fresher tires, meaning those produced at a later date. One characteristic of racing tires is that the older a tire is, the less performance it will provide. Each tire contains specific chemicals to help it produce grip when heated. If those chemicals evaporate over a period of time, the good characteristics also evaporate, so to speak. Fresh tires will outperform older tires-period.
On-track results can depend...
On-track results can depend on the ability of the tires to carry the car. It helps when you understand the limitations of a tire's performance.
If there is a way to tell a tire's production date or the production run numbers, this will help you pick sets of tires with the same age. Even if they are older, you must have the same age tires in the four that make up each set. Having three older tires and one fresh one will throw the setup off considerably.
Tire distributors don't like to deal with this issue because it is a pain to keep track of the age of their tires. Ask your tire vendor if they can sort the tires by age if they don't already.
Select your tires based on these considerations:
* Hardness or compound (choice usually offered in dirt racing)
* Tread design (dirt tires, based on temperature and track condition for all events)
The proper way to insert a...
The proper way to insert a temperature probe is to push it in at a 45 degree angle. Take the outside temperatures in from the outside edge of the tire approximately 1 to 1 1/2 inches. Allow enough time for the reading to settle before recording and moving on.
For every type and use of a racing tire, there is an optimum pressure that will provide the maximum amount of traction. The tires normally get their first airing with nitrogen gas that contains very little moisture. There are air pumps that remove much of the moisture in ambient air. In any event, if the gas in your tires has water mixed with it, pressures will increase more so than dry gas. You should start with the most pressure you can get away with and then have the gas expand to the optimum pressures once the tires are heated.
Safety Note: Never over-inflate racing tires. Teams do this with bias tires to stretch the cords to get the tire size consistent and to keep the stagger. The tire manufacturer will tell you how high you can safely go. Extreme inflation pressures have been known to injure and kill team members. The tire will come off the rim at some point, and the force is powerful enough to seriously injure you.
Do not use air hose ends that can be clamped onto the valve stem. If you become distracted, the tire can over-inflate by accident.
Using excessively high or...
Using excessively high or low tire pressures will cause the tire to have a smaller contact patch area and therefore reduce traction.
The entire width of the tire...
The entire width of the tire may be on the ground, but the whole area of the contact patch is not exerting the maximum pressure on the racing surface.
By arranging tire sizes, it's...
By arranging tire sizes, it's possible to correct a rear stagger problem that arises after the tires have been run and one of them grows more than the other. A 1/4-inch growth probably won't make a significant difference in handling, but a 1/2-inch growth or more will. By planning out the front and rear tire sizes, this errant stagger can be corrected by switching left-side or right-side tires, depending on which rear tire grows.
Stagger is the difference...
Stagger is the difference in circumference of two tires on the same end of the car. Measure the stagger around each tire near the middle of the tread. Subtract the two measurements to find stagger, or rollout, as it is sometimes called. Always inflate to racing pressures before measuring.
It is important to take tire temperatures when evaluating the car's setup. The temperatures can indicate how well each tire is working in conjunction with the other three. We set camber and tire pressures based on tire temperature.
To take tire temperatures properly, read the temperatures in three places across the face of the tire with a tire temperature probe. This instrument has a needle-like end inserted into the rubber to get the inside temperature. It should be inserted into the rubber at a 45 degree angle. Measurements should be taken at the edges about 1 inch inside the edge of the tire and at the middle of the tire.
Give the instrument time to react to the temperature of the tire. Once the reading stabilizes, record the amount and move on to the next reading. Don't be in too much of a hurry to do this. Many decisions will be made based on the temperature readings, so they must be accurate.
Even when desired stagger amounts are known, tires can be mounted in a manner to allow changes to improve the car if there are unexpected stagger changes. Once the tires get hot, the gas expands and the bias tires stretch. By putting the correct stagger on the rear, the front stagger can be set so that the tires can be swapped on each side of the car to affect the rear stagger if one of the rear tires changes its size after being run.
To find stagger the easy way,...
To find stagger the easy way, follow this simple method and never subtract tire sizes again. Measure the larger tire first. Then remember the number.
Example: A rear stagger amount of 2 1/2 inches is needed. The right-rear (RR) tire is 86 inches in circumference, and the left-rear (LR) tire is 83.5 inches around. One of the rear tires will grow, causing either an increase or decrease in stagger, depending upon which tire changes size. If the same stagger is on the front, but at a larger size, swap either left-side or right-side tires to correct the problem.
The tire stagger must match the racetrack and groove radius. Do not correct handling problems with excess or deficient stagger. For every track, there is an optimum stagger for the rear tires. The need for correct stagger is even greater if you're using a locked-spool rear differential.
The spool will need a stagger that is an average of the radii that the tire will experience in the turns. Few driving lines result in a single, constant radius. The driving line through a turn is more like a parabola, or constantly changing radius, with the smallest radius in the middle portion of the turns.
Wrap the tape measure around...
Wrap the tape measure around the smaller tire and mark where the large tire stagger number falls near the end of the tape. Read the measurement from the end and you have the stagger.
A Detroit Locker rear differential unlocks when going into the turns and locks back up upon acceleration. For this type of rearend, match the stagger to the radius of the last third of the turn. This may be less stagger than what might have been needed at the very tightest portion of the mid-turn.
When running on a set of tires at race speeds, there are three indications of how well the tires are working. Those are tire temperatures, tire pressures, and tire wear. Pressure and wear are fairly easy to read for both asphalt and dirt teams. Dirt racers may have a difficult time getting temperature readings because of the way heat bleeds off the tire after a run.
The temperatures will indicate how well the tire footprint is working. Ideally, the heat should be nearly even across the face of the tire. The temperature is usually taken in three places. Some teams prefer to see a little more heat on the inside (toward the inside of the racetrack for this purpose) of the tire, but the progression of the heat should be increasing steadily from the outside to the inside in any event.
A front tire with improper...
A front tire with improper camber settings will not have a uniform contact patch profile. Adjust the front cambers using tire temperature and/or wear patterns to maximize the pressure distribution on the contact patch. This sketch shows how the contact patch pressure distribution should look...
Don't make major changes to tire pressures or front cambers based on the tire temperatures until you've had a chance to run the car at full speed for more than five laps. Maximum temperatures allow teams to see the true picture of what the tires are doing. If the temperatures are lower or higher in the middle of the tire, it is an indication of lower or higher than adequate tire pressures. Increase or decrease the tire pressures in 1- or 2-pound increments until the temperatures even out.
If the temperatures at either side of the tire are higher than the other side of the same tire on the front of the car, the cambers probably need to be changed. Having the correct camber is necessary in order for the tire to generate the largest footprint and give the most traction. This should be taken care of right away during practice. Do not make handling changes until the tires have the correct pressures and cambers.
The tire wear also tells a lot about how a tire is working. By measuring the depth of the tire grooves or wear slots across the face of the tire, you can see if the cambers and pressures are correct. This is especially useful for situations in which taking tire temperatures is not practical.
Wear patterns are especially useful for dirt applications. Look at the tire after enough laps have been run for wear to be measured. Wear on a cambered wheel can tell a lot about how the selected camber works with a particular setup. If the wear is on the outside on any of the four tires, the pressures are probably too low. Excess wear on the middle of the tire indicates that the pressure is too high.
...and this one shows excess...
...and this one shows excess camber where the outer portion of the tire contact patch is not being utilized fully.
It is important to react to any tire problems quickly, whether they are front camber issues, tire pressures, or stagger. As you test and race, setup adjustments will not be correct if the tires don't have what they need in order to provide a good footprint.
Adjust the pressures first, then the camber, and run the car. After you are up to speed and have run several sets of laps, see where the stagger has gone. We are mostly concerned with the rear stagger, but note if a front tire grows more than normal. This may indicate a bad tire or one that is being overused. The tire temperatures will back up the tire growth if the tire is working too hard.
Make all changes quickly after noting a problem. Correct a stagger problem right away, as well, so that you don't chase the setup to correct a loose or tight-off condition made worse by incorrect stagger.
Once a set of tires has been used for practice or a race, mark how many laps the tires have run and note unusual tire growth or tire temperatures on the problem tire. If the car runs loose all night in the race, chances are the RR tire has been hot all along. Recording this information may save problems if the car begins to act funny while practicing with this set of tires in the future.
Store the tires in a cool and dark place. If convenient, cover the tires to prevent exposure to the air. Used tires can always be used in practice or testing, but keep in mind that performance won't be as good as it would be with newer tires.
Once the best balanced setup for the car has been attained, the driver and the tires can use it to do their jobs. If tire cambers, pressures, and stagger have been properly eval-uated, it is up to the driver to take advantage of that performance and drive the car to its full potential. Winning performance begins where the rubber meets the track.