Tire Instrumentation

Choosing a pyrometer? What is better probe type or Infrared? The answer really depends on the application. Most tire engineers prefer the probe type for tires as the probe gets down to the cord. At the cord, the tire heat is un-affected by out side factors and the surface rubber insulates the heat for long enough for you to take readings. There is also an elastic stretching of the rubber near the cord that creates heat as well. The bottom line is that probe type pyrometers are best for specific applications such as tires.

On the other hand, Infrared pyrometers are versatile and can be used to check just about any kind of surface temperatures. You can find sources of heat which will affect the driver, locate dead engine cylinders, check track temperatures, brakes and just about anything. You can even use them on tires. However, this is a bit of a compromise. You will be getting a surface reading that will be 10-40 degrees cooler than temps taken with a probe type pyrometer. You will also get variances from the engine and brake heat. Further, the track temperature will cool off the surface very quickly. A tire with camber in it will ride on the inside edge when the car is rolling back to the pits. The area that is in contact with the track will cool down at a different rate than the rest of the tire. Your readings will not be as relative as compared to probe readings.

If you accept the limitations, the Infrared pyrometers will work for tires but will not be relative to probe readings nor will the delineation be as good. Using the right tool for the right job always produces better results. Just as the probe type is better for tires, the infrared type is better for most other surface temps. The probe type is designed to be submerged in rubber and does not work well for things like track temperatures. For rubber, probe type is best. For surface measurements, the infrared stands out.

Durometers can be a very effective tool for selecting the best tires from a new stack as well as helping to decide when your used set needs replacement.

Durometers measure the relative hardness of the rubber on your racing tires. In order to get the most accurate results you need to follow a standard routine. You must apply equal pressure to the durometer each time you take a reading. If you press the durometer down very hard one time and then very soft the next your results will vary due to the uneven hand pressure.

You must also take a measurement quickly and be consistent when taking readings. If you place the durometer on your race tire and leave it in the same spot for several seconds the rubber will deform, giving you a false reading. The rubber conforming around the durometer-testing probe will create the false reading.

For the best results you should take your durometer readings as quickly as possible. Simply place the durometer on the tire surface with the footpad at a slight angle. Lightly roll the footpad until it is flat on the tire, take your reading and record the measurement.

For accurate results you must also consider the temperature of the tire. Hot tires will be softer than cool tires. If you are looking for the softest tires in a stack then you need to take care that you take durometer readings in equal environmental conditions. For example, if you take a reading on a tire that is in the hot sun your durometer reading will be softer than an equal compound tire that is in the shade. The side of a tire facing direct sunlight will generally read softer than the side facing the shade. The temperature difference results in a durometer reading difference.

Temperature can affect the tires that are on your car. Tires that have heat from a hot lap session will give you a softer durometer reading than tires that have not yet been run. If you check the tires with a pyrometer you can insure that the tires are the same temperatures to insure more accurate results.

On tires that have been run be sure to prep the tire surface for a proper durometer reading. You should take a small scraper and remove any loose rubber from the tire surface. Removing the loose rubber requires little effort on hot tires. Cold tires require a little elbow grease to get down to the true tire surface.

When race tires are hot they are very sticky. Riding around the track on a cool down lap and driving through the pits allows the hot tires to pick up the loose bits of rubber that are lying on the track surface. The loose rubber adheres unevenly to the tire surface causing false readings. The loose rubber must be removed with a scraper to allow the durometer footpad to sit flat on the actual tire contact patch. You must remove the loose rubber to get accurate durometer results. If you are checking your tire wear with a tread depth gauge you need to remove the loose rubber as well.

Remember, durometer hardness is only part of the tire equation. Tire compound, chemical composition, tire tread gauge, sidewall design, heat cycles and tire wear are all factors that affect the performance of your tires. Considering all the variables and using your durometer measurements will help you to select the right tire for the right conditions. Proper use of the durometer will allow you to track the condition of tires, giving you the chance to replace them before the tires get too hard for competition.

Bleeders are designed to relieve the excess air pressure build up due to the normal heating of tires. Proper setting of relief valves is paramount to their function. Loosening the jamb nut and turning the cap is all it takes to make an adjustment. A tighter cap will allow for higher pressures where as a looser setting on the cap will allow for a lower pressure setting.

Consistency is the key when setting the bleeders. Making the adjustments the same way each time will increase your relative accuracy and make adjustments more reliable. When making adjustments it is best to set the tire pressure about 3-4 pounds higher than the desired pressure. Setting the tire at a higher pressure will allow you to loosen the cap until you hear a maximum flow of air. Next, you slowly turn the cap until the air completely stops. You can then fine-tune the cap adjustment until you are at the desired pressure. By allowing the air to free flow out and then slowly tightening the cap you reduce the chance of improperly setting the pressure due to variables such as dirt or liquid on the seal.

To get a visual look at when the air has completely stopped coming out of the bleeder you can spray a small amount of Windex glass cleaner on the opening to see when the bubbles stop. Even small amounts of air flowing out of the valve will lower your pressures on the track so be sure to be precise when setting the valve. Hearing air flow at the racetrack can be difficult due to all the engine noise so a visual look is very helpful.

Maintenance of your bleeders is very important to allow you to get consistent settings. If you regularly maintain the valves then simply cleaning the seat and poppet seal with a clean damp rag is sufficient. Avoid the use of cleaners that can damage the rubber seal. Look for a factory installed screen to keep dirt and debris from entering the valve from the inside of the tire.

Inspect the spring for squareness and be sure the ends are free of burrs. File off any burrs. It can be helpful to use a very small amount of white grease or graphite on the ends of the springs to assist in getting repeatable settings. Be sure to wipe off any excess.

Some people keep a supply of bleeders in their tool box that are marked at a preset pressure so that they can plug them into a Quick Change Adaptor with assurance of a correctly set valve. For last minute changes the Quick Change Adaptor makes for a nice benefit. Setting tools and Quick Change Adaptors can be used to assist in presetting but you can also set the valves right on the wheel.

If you need the valve to hold higher pressures, be sure to use the shim that is provided. Stretching the spring is never a good idea. Bleeder springs are manufactured to be true and square. Stretching them distorts and bends the spring making the operation of the valve very unpredictable as the out of shape spring rotates and moves the poppet off center on the seat.

Consistency and proper bleeder maintenance will provide you with more consistent stagger and tire pressures allowing you to start races at full pressure so that you can race confidently into the first turn.

Ever wonder when to buy that new set of tires? Can you get another week out of the old set and still be competitive. If you keep good notes then you can get an idea of when to step up for some new boots.

You can use a durometer and track the hardness of the tires from when they are new and log your tests results as they age. The tires will harden with age, which can be tracked with a durometer. When using a durometer make sure that the durometer is used on tires of the same temperature to insure relative measurements. Hot tires are going to be softer than cooler tires. You will notice that tires sitting in the hot sun are softer than those that are shaded. You can use a pyrometer to improve the consistency from durometer readings.

You can also track the tire temps after a run. New tires make more heat than used tires. Worn out tires will not produce as much friction to produce tire heat. By tracking the temperature of the tires after a run, you will learn to anticipate when the temps are falling off too much. If you are diligent in your monitoring you will know when to hit the tire truck for that new set.

You can also use a tread depth gauge to check the amount of tire wear. On many tires, the grip falls off dramatically at a given wear depth. When you feel like your tires have quit, then check the depth with a tread depth gauge and write the numbers in your notebook. You will learn to anticipate when you are approaching the wear depth that makes you want a new set. Over time you can learn to predict when you have gotten the most out of your set of tires. You may find that the fall of in each corner is a bit different. The LF may work to a deeper depth than the left rear because it does not go through the spinning created by your awesome horsepower.

Another good idea is to track is the number heat cycles your tires experience. Each time your tires get hot they release chemicals from deep within the rubber. As the chemicals are released the tires lose some of their grip. You can see tires that are hardly worn lose their grip due to heat cycles. Count the number of heat cycles that your tires go through and you may find a repeatable pattern that lets you know when to get that new set.