Setup Dev 04 - Tires
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Obviously, tires are the contact between our vehicle and the track surface. The "contact patch" of the tire is literally the patch of rubber that is making contact with the road surface. It is no more then a few inches at a time. Because the contact patch is so small, every little bit of additional contact area is worth more grip then any other adjustment you can make to your car, making the tires easily the most important aspect of your setup. Many factors are at work for an optimal contact patch, and we will discuss each as we progress in these articles. For now, we will focus on the tire itself and how to optimize it. Our tires are designed (or simulated) to operate at an optimal temperature of roughly 200 degrees Fahrenheit. In a perfect world all four of our tires would be at 200 degrees at all times, but this is not going to be happening. We can easily determine our tire temperatures in the garage/setup screens, displayed as Inner, Middle, and Outer temperature readings. Each are going to have a different reading depending on camber, caster, toe, springs, antiroll bars, and tire pressures. Every adjustment you make to the other chassis components will require you to retest and adjust your tire pressures. It is widely accepted that in a road racing setup the inner temperature of your tire should be the hottest, with the middle being next in line and the outer temperature being the coolest of the three. Many use a 10-15 degree spread as a target to aim for as in the example below; (Outer, Middle, Inner)
While this is a good starting point, these settings are not a true 'optimization' of your contact patch. The first question you must answer is, "Where are these temperatures happening?". Reading temperatures after a straight is not indicative of what the tire is doing in the corners. It is the corners where the tires need optimal contact patch, not the straights. You must get your readings as soon after a corner as possible, and the tires must be at full pressure. This means to optimize just one tire, you will need to complete multiple laps before coming to the corner in which you plan to get your reading from. On the same note, the corner that you choose should be the corner that generates the most heat in that specific tire. This may be a different corner of the track for each tire. What you are looking for is not a simple 10-degree spread, but the same temperature across all three points of the tire while in the corner. If the inside is 200 degrees, then the outside should also be at 200 degrees and the middle should also be near 200 degrees. You certainly will not want the outside temperatures higher then the inside temperatures, so you will end up with the outside slightly cooler in most instances. The middle temperature is at its optimum if directly between the inner and outer temperatures, as shown below; (Outer, Middle, Inner)
Camber is your primary weapon to achieve the most uniform inner and outer temperatures. Air pressure is what you will use to fine tune the middle temperature. Because you are taking your readings during times that the tires are being used at their most, you will be able to optimize your contact patch more effectively. While I have been talking about the contact patch of the tire, there is also another part of the tire that you should keep in mind; the sidewall. While the sidewall is not making contact with the track, it is still a vital piece of your setup equation as a spring. As you optimize your tire temperatures, you are also changing the spring layout of your car. One pound of air pressure can be equal to 15 - 25 lbs of spring rate, meaning you may now need to go back and adjust your corner-springs to achieve that neutral feel again. Tires are a great way to "read" your overall setup package and driving style. If your front tires are hotter than your rear tires then you may need more grip to the front of the car, either mechanical or aerodynamic. You could just as easily remove grip from the rear to balance the front-to-rear temperatures. A front-to-rear difference in tire temperatures can not only tell you if your setup is balanced, but it also can tell you if your driving is good or bad. Sliding the car around will bring higher temperatures and can explain a difference in tire temperatures. Adjust your driving as needed as well. A final note: A tire, by nature, will never achieve optimal grip without some degree of slip. The amount of this slip is measured in degrees and is known as "slip angle". If the radius of a corner is 80 degrees, you will want your tires to be on an arch of a few degrees more. Four-to-eight degrees of slip will actually grip more then zero degrees of slip. Exceed the optimal slip angle and you lose grip. The 'slip' causes the rubber of a tire to generate a 'suction' to the road surface as the rubber is continuously trying to contract back to its natural form. Upon contraction of the rubber back into its static form, it pulls the tire, and car, into a tighter turn. This pulling is additional grip. Keeping your tires in the optimal slip angle is the difference between a fast driver and an alien driver. This is all done by feel and experience, as there is no display in our setup screen to inform us that we are in that slip angle sweet spot while driving on the track. TIP: You will never stop adjusting tire pressures. Just get use to checking your tire temperatures after every time you are on track or make any change to your setup. You will spend more time adjusting tires then any other setup option.
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