Tire temperatures reveal how a supermodified is handling
By Group R Motorsports owner Bob Bogwicz
The goal to measuring tire temperatures is to push the probe past the rubber tread of the tire and into the underlying cord structure of the tire. It is here, below the surface of the tire, where the tire will “speak the truth” of how it is being worked on the racecar.
In earlier Supermodified Tech Knowledge columns, I mentioned the concept of tire temperatures and that this concept would be covered at another time. Well, that time has arrived and you are about to learn one of the most useful and vital tools that a race team has in their bag of tricks.
There is only one method that a crew chief can use that will give hard numbers that translates into the handling of the racecar. This method is immune to a driver’s subjectivity, opinion or mood. The method is to use tire temperatures. Tire temperatures reveal how the car is handling in the corners in concrete, quantitative terms.
But, like many other things in life, there’s more to it than just “taking a tire’s temperature”. Obtaining tire temperatures requires the proper tools, a consistent measurement method and proper technique. Once the tire temperatures are measured, a crew chief must have the knowledge and experience to interpret the data into information that will be used for one thing: to make the racecar go FASTER!
The tool used to measure tire temperatures is called a pyrometer. An example of a digital pyrometer is shown in Figure 1. A pyrometer consists of a hand-held “wand” that has a needle-like probe at its tip. The wand is connected via a cable to a hand-held control unit.
The control unit has a display that reads the temperature measured by the probe. The proper method of obtaining tire temperatures is to insert the probe, at about a 45 degree angle, into the tread surface of the tire. However, one does not want to measure the surface temperature of the tire. The goal to measuring tire temperatures is to push the probe past the rubber tread of the tire and into the underlying cord structure of the tire. It is here, below the surface of the tire, where the tire will “speak the truth” of how it is being worked on the racecar.
Once the probe is inserted into the cords of the tire, the readout will display the temperature of that point in the tire. If the probe was initially sitting in the toolbox, it will be reading the ambient air temperature, which will be much cooler than a tire that has just come off the track. If this is the case, the user of the pyrometer must allow the readout to go from the ambient air temperature reading to the tire temperature reading. Once the temperature stops rising, the user can record that temperature.
As I will explain next, a tire must be measured at three points across its tread for tire temperatures to be effective. Therefore, it is imperative that the crewman taking the temperature measurements keeps the probe warm between measurement points (not allowing the probe to cool off towards the air temperature) by placing a finger on the probe between measurement points and dragging the probe across the surface of the tire between points. This technique (which is described in the Steve Smith Autosports book “Paved Track Stock Car Technology”) will speed up the measurement process and provide for more accurate readings.
A quick side note to race teams. Don’t use an infrared temperature “gun” for measuring tire temperatures. This type of measuring device only reads the surface of the tire which will yield inaccurate numbers. The only way to measure tire temps is with a probe type pyrometer as shown in Figure 1. This device will probe the temperature of the internal structure of the tire which, for this purpose, “is where the action is”.
So, we’ve talked about the tool and technique used to measure tire temperatures. Now let’s talk about the method. Before we start, we must agree upon a naming convention that clearly describes a place on a tire. We all need to be on the same page with the terms “inside”, “middle” and “outside”. Here is the convention: a point on a tire that is closer to the inside of the track (towards the infield) is considered “inside”. A point on a tire that is closer to the outside of the track (towards the grandstands) is considered “outside” and the middle is, well, the middle. This convention is shown graphically in Figure 2 by illustrating what we mean by “inside’, “middle” and “outside” given the front view of a left-side and a right-side tire.
Like I said before, a tire’s temperature is measured at three points across the face of the tread: an outside point, a middle point and an inside point. The middle point is of course right at the midway point of the tires contact patch. The inside and outside points are measures between 1 and 2 inches from their respective edge of the contact patch. Measuring three points across the face of the tire (as opposed to one or two) is necessary because the interpretation of the data depends on the comparison of the temperatures to find how an individual tire is being worked.
Speed and consistency are vital for accurate tire temperatures. For temperatures to be meaningful towards determining a racecar’s handling characteristics, one must take the measurements quickly. This means measuring three points on four tires, for a total of twelve readings, as quickly as possible.
The issue at hand is that tires cool off quickly when at rest. The entire surface area of the tire is in contact with a big ol’ mass of air called “the atmosphere” and that sucks the heat away quite fast.
On my Group R Motorsports #09 Supermodified, I place one person in charge of taking the tire temperatures. I tell that crew member to knock other crew members out-of-the-way, if necessary, to get to the tires.
Another issue with taking quick readings is that time elapses between the car slowing down to come in the pits and when it has stopped in the pit stall. This amount of time gives the tire more opportunity to cool down and yield invalid temperature readings.
If you are familiar with Spencer Speedway (a GREAT little track, just outside of Rochester, NY), the pit entrance is at the end of the front straightaway in turn one. When we get the yellow flag to end a hot lap session or a race, they don’t want us to slam on the brakes and head for the pits. They want us to slow down gradually over another lap around the track and THEN head for the pits. Once in the pits, you have to negotiate a couple of sharp corners and most likely run over a grassy area to get to your trailer. I don’t even bother with tire temps at Spencer because by the time my crew has an opportunity to measure tire temps, they have cooled down to the point where the data is meaningless.
Technically, the only true method of recording tire temps is to have the car stop on the straightaway immediately after a turn. A team would most likely have to have the track all to itself to do this. This is called a “private test session”. English translation: “open your wallet for a track rental”!
A consistent technique of measuring tire temperatures is also a key element of accurate readings. Even while a crew member is going from one tire to another, taking temperatures, the tires are cooling off. Using four crew members and four pyrometers is a possible solution, but that would be too easy.
Beside, I have these annoying things in my life called a mortgage and a car payment, so I can only afford just one pyrometer.
Consistency will help this problem along with quickness of measurement. If the temperatures are taken the same way EVERY time, this will help in interpreting the data.
The technique I told my crew member to use is to start at the right front tire and measure inside, middle and outside. When he does this, another crew member is right there with him to write the temperatures on the tires with special chalk. He then proceeds to the right rear tire, measuring inside, middle, outside, then to the three left rear temps and on to the left front.
When he is finished with all four tires, he then takes the right front temps one more time. The second crew member will write these temps down and circle them to distinguish them from the first readings of the right front. The reason I have them take the right front temps twice is to determine how much it has cooled off while he circled the car, aiding in data accuracy.
My crew member uses this method EVERY TIME he takes tire temps. His speed and consistency give me confidence in the numbers he has obtained.
So, we’ve collected twelve tire temperatures. Now, what do we do? In the February installment of Supermodified Tech Knowledge, I mentioned how the camber settings can be fine tuned using tire temps. So, here’s an example:
Let’s look at a single tire first: the right front. Figure 3 shows the temps of a right front tire after a hot lap session. Note that there is a spread of 20 degrees between the inside edge and the outside edge, the middle temp is between the two edges and the maximum temp is within a recommended range. This tire is working properly. On a supermodified, any temp over 210 degrees is cause for concern.
Because of negative camber (the top of the tire tilted towards the center of the car), the inside edge is warmer than the middle or outside. This is because this part of the tire is being worked around the entire racetrack; the straightaway AND the turns. The outside edge is coolest because it gets worked only in the corners. While the car is going down the straightaway, the outside edge (and to a lesser extent, the middle portion of the tire) has a chance to “cool down”. The middle part of the tire should have a temperature that is in between the inside temp and the outside temp.
The tire temperatures in Figure 4 show a right front tire with too much negative camber. The main sign of trouble is the temperature spread. There is a 60 degree difference between the inside and outside edge, which is too much. In addition, the inside edge is running about 20 warmer than it should and the outside edge is about 20 degrees cooler than it should be. The crew chief needs to reduce the negative camber to get the temperature pattern as shown in Figure 3.
Tire temperatures can also be used to find out if the tire pressure is correct. Figure 5 shows the temps of a tire that has too much tire pressure. Even though the temperature of the edges looks acceptable, the center temp is too high, indicating that the tire is over-inflated and the tire tread has a “crown” to it. If the middle temp were to be too low, then under-inflation is the likely problem.
The same observations will be applied to the left front tire to make it work as effectively as possible.
The example above illustrates how tire temperatures can be used to determine how a single tire is working. By using average tire temperatures (adding the three temps of a tire and dividing this total by three), a crew chief can compare how one tire works with respect to the others and actually diagnose a loose or tight condition, even without any comments from the driver. Using tire temperatures to decide a loose or tight condition is pretty high-level stuff and takes a great deal of experience to get it right because it is more art than science.
For the next installment of Supermodified Tech Knowledge, we’ll talk about tire stagger and how it is used to get a racecar to turn left as quickly as possible.
Thank you for your questions about supermodified technology. Special thanks this month to throughthecatchfence for the nice comments about these articles on Wing Side Up. I’m glad you like them. If you have something you’d like to see covered in a future Supermodified Tech Knowledge column, you can contact me at motosports@groupRtech.com. Follow me @groupRmtrsports and submit questions via Twitter as well.
When The Bogwan isn’t bossing his crew members around about tire probing techniques, he’s burning rubber getting to the mailbox for your supermodified tech questions. If you want to keep his tires turning and need more supermodified tech knowledge, leave a comment below or Hit the Wailbag. The Bogwan will have your answers right after he checks his temperatures.