Everything we do with regards to chassis setup is geared to making the most from our tires available grip. There’s no point in spending money on expensive grippy tires if we are not making use of all the grip that they have available. Recording our tires temperatures when at the track, then taking action on this data, is one of the tools we have to make sure that we’re making the maximum use of the tires available traction.
With this data we can tell if a car has a tendency for understeer or oversteer. We can tell if we have the cross weight percentages set correct. We can also tell if there would be benefit from moving static weight. What we cannot monitor is transitional handling. This is handling that happens over a short period of time in the corner sequence. Shock absorbers and a good driver, with proper feedback, have the greatest impact on transitional handling to help get shock valving set correctly. Taking tire temperatures is an inexpensive data-acquisition system – it just takes the time and procedure to do it properly.
Racing Tires Love Heat
(Showing my age) Like the 1984 Glenn Frey song “The Heat is On” from the soundtrack for the Eddie Murphy film “Beverly Hills Cop”, R-comp tires LOVE some heat! R-compound tires and DOT tires with a treadwear near 200 are designed to get more grippy and “wake up” as heat is generated in them. This is because heat excites the molecules of the polymer that make up the tire material. This excitement softens the rubber, making it more pliable allowing it to get into the imperfections of the track surface. This creates a greater mechanical interface between the tire material and the track surface – which means more grip!
Camber and Tire Pressure
Many people can go into the weeds with chassis setup and handling issues. Spending hours researching springs rates, sway bars, roll center, weight transfer, vertical load and body roll to name a few. Although important to ensure we have a properly handling car, if we are concerned with maximizing the tires contact patch, and minimizing waste, the two tunable areas that matter are – camber and tire pressure. Taking tire temperature yields valuable information into the effectiveness of the tire contact patch. We can learn how the driver is affecting handling, if the car has a tendency for oversteer or understeer, and is static weight distributed evenly.
Procedure to Record Tire Temperatures
Now that we’ve established we get valuable information from tire temperature data. Lets review the procedure to do this properly so we get consistent, valuable, actionable data.
- Don’t take temperatures after the cooldown lap. As the name implies, the tires will cool down before you can get any useful information.
- A few laps into your session, after you’ve developed speed and put some heat in the tires, drive through the hot pit lane and maybe stop near the black flag station. Don’t over brake coming in as this may yield misleading information.
- Drive your normal racing line with normal driver inputs. Come to a stop gently so as not to heat up the front tires too much.
- If you have someone with you after you come to a stop have them take and record the temperatures. If you are your own crew chief, mechanic and driver do the best you can to get the temperatures as quickly as possible.
- You may be able to get the corner worker working Pit Out or the Black Flag Station to guard your pyrometer and notebook for you while you’re on track.
- When taking tire temperature, it’s best to use a pyrometer with a needle that can penetrate the tire surface. Infrared pyrometers take the temperature quicker but you only get temperatures at the tire surface which most likely has cooled down by the time you take your reading. By penetrating the tire surface you get a more record reading. (Here are a couple great options we offer: Joes Racing Products Deluxe Racing Pyrometer, Longacre AccuTech™ Deluxe Digital Pyrometer, Longacre Deluxe Memory Tire Pyrometer and Longacre Standard Memory Tire Pyrometer,).
- Record temperatures about one inch from the inside edge of the tire, the middle of the tire and one inch from the outside edge. You can start from the inside working out or the outside working in but when you record do it the same way each time. Be consistent.
- Start from the same corner of the car each time and work your way around to get all four tires. Again do it the same way each time. Also, and this is a critical part of the process. After recording the temperature of all four tires record the first tire’s temperature again. The temperature of the other three tires will have dropped by the time you record the temperature. You can use this information to extrapolate what the temperatures of those tires were when the process started.
- You can keep heat in the probe by holding your thumb or finger over the needle while taking the temps.
- When recording data slide the probe over the tire surface when moving the probe across the tire. This helps keep heat in the the probe while moving it across the tire and reduces the time needed for the probe to get back to peak temperature.
- You also want to capture tire pressures as well. Since tire temperatures will change more than pressure since coming off track.
- Take tire temperatures first then go back and take tire pressures in the same order that you did the temperatures. Also record tire pressures before you go on track so you can gauge how much pressure build you gain during the session. Also record the ambient air temperatures at the track. And if you have an infrared pyrometer record the track temperature as well. Do this after recording tire temperatures and pressures. Weather conditions change from session to session.
- Once in a while check tire pressures again in the pits after about 5 to 10 minutes. If the pressure is higher than when you first recorded tire pressures it could be that heat is being added from the brakes. If pressures go up on this second recording you may have a potential brake heat problem.
Using This Data
Once we have this data here’s how we can use it:
- At each individual tire, the inside temperature should be slightly hotter than the outside, with the middle temperature right in between. If this is not the case we will diagnose some possible causes for these differences later.
- Much of our data analysis will come from the average temperature for each tire. To get this simply add the inner, middle and outer temperatures, and then divide by three. The goal is to get the average temperature of all four tires to be about the same. This means all four tires are providing the same amount of work.
- If one tire is hotter than the others it is doing too much work. If one tire is cooler than the others it is not doing enough work.
- You can also compare front average compared with the rear, left compared with right, and the diagonal average temperatures.
You can also see if the temperatures you record are in the optimal range for the tire that you are running. Typical operating range for an R-compound tire is between 180 degrees and 200 degrees Fahrenheit. A street tire will run a bit cooler and a race tire a bit hotter. You can use Google to find specific information for your tire.
- If tire temperatures are too cool perhaps the driver is not driving the car as hard as he or she can be. Or perhaps weather conditions at the track are not optimal and too cool.
- If temperatures are above the optimal range for the tire, perhaps ambient conditions are too hot and the driver needs to look to maintain the tires during the session.
Using This Data to Make Chassis Adjustments
We now have valuable information and can look to make some adjustments on the chassis to make some corrections.
- If fronts are hotter than the rear or rears hotter than fronts a change in the spring rate or sway bar may help even this out. Stiffen the springs or sway bars at the end that is cooler. If you are happy with spring rates and sway bars adding or removing front toe may add or remove heat at the front.
- For road racing we want a near 50/50 weight distribution so left and right side should be about equal. Although most tracks do tend to have a few more right hand turns compared with left or vice versa. Keep this in mind when comparing left versus right side average temperatures.
- If diagonal temperatures are off you can look at cross weight to put heat into the cooler diagonal. If one specific tire is hotter or cooler more or less static weight at that corner may help to get this tire working more equally with the other three tires. Be forewarned, if static weight is changed you may need to rebalance the car.
Looking at the individual tire temperatures:
- If the inside edge is too hot there’s too much negative camber.
- If the outside edge is too hot there’s not enough negative camber.
Looking at the middle of the tire. (Tire pressures).
- The middle of the tire’s temperature should be right in the middle of the inner and outer temperatures. If it’s too hot then there’s too much pressure in the tire. If the middle of the tire is too cool then there is not enough pressure in the tire.
People talk about “scrubbing” or heat cycling tires. Here’s what that actually does. Heating of the tire from a track session weakens the bonds of the elastic polymer of the tire. This track session will also bend and stretch the tire material. This helps to more consistently align the granular structure of the elastic tread. As the tire is heated, the weakest molecular bonds get broken and are then realigned by the dynamic forces of the tread acting on the pavement. As the tire cools those bonds will relink in a stronger, more consistently aligned fashion.
Being diligent and adding taking tire temperatures to your weekend routine, along with taking tire pressures, will provide valuable insight as to whether you are making the most of each tire. And helps provide a direction for chassis tuning without the addition of any expensive equipment.