Learn about race car tire contact patches
By Group R Motorsports owner Bob Bogwicz
The race car and the racetrack have only one thing in common: the contact patches of the tires.
Let’s start with an introduction: my name is Bob Bogwicz, better know as “The Bogwan” and I’ve been coming to Oswego Speedway since 1970 and I’ve been involved with the racing at Oswego, one way or another, ever since. I even worked as a track photographer. But I was no shutterbug. I just wanted the free pass to get into the races! That also includes racing at the “Big O” in small blocks and supermodifieds since 1998. I am an electrical engineer living in Rochester, NY and spend my non-racing time as the owner of Group R Technology, Inc providing electrical engineering design services.
If you recall “back in the day” when Bobby G. would webcast Wailing with Wing Side Up every Monday evening, I would be on once a month to pass along my technical knowledge of supermodifieds and hopefully eat chicken wings and drink PBR (when in Rome….).
My goal with this column is to educate our fans with knowledge about supermodifieds, small block supers and racing in general. I will do my best to keep this tech as understandable and entertaining as possible. We’ll discuss topics such as tires, shocks, springs, brakes, panhard bars, etc. and how they relate to the handling of a race car. In the end, I hope this enriches your supermodified experience at whatever track you choose to attend.
When it comes to the handling of a race car, virtually every adjustment made to the car’s chassis is to maximize the grip of the tires to the racing surface to get the car to turn left as fast as possible. This concept is our “prime objective” and it will be repeated in this column over and over. The race car and the racetrack have only one thing in common: the contact patches of the tires. These four contact patches are, no pun intended, “where the rubber meets the road”. The relationship between the track surface and the contact patches of the tires is THE most important aspect of race car handling.
But, let’s put the concept of tire contact patches into perspective: The contact patch of a tire has an area that is no larger than the sole of a size 11 shoe. Imagine a 400+ horsepower Small Block Super flying into Oswego’s turn 1 at 115 MPH on 4 size eleven shoes. The margin of error in the car’s set-up is very small, given the high speeds and surprisingly small contact with the track surface. Thus, race teams need to be knowledgeable with the characteristics of racing tires and how to make adjustments to the car and the tire itself to maximize the grip with the track surface.
The most common adjustment to make is the tire pressure. A race tire, like a street tire uses pressurized air to support the tire. This pressurization combined with the carcass of the tire supports the racecar’s chassis (by the way, the term “chassis” describes the car and its various suspension parts). The tire manufacturer specifies a pressure range that is ideal for a particular tire. Tire pressures outside this range will result in a less than ideal tire contact patch and thus, not meet out prime goal of maximum grip.
With a passenger tire, the main concern of a slightly under-inflated tire is reduced fuel mileage because the engine has to work harder to make the tire roll. Over-inflation of a passenger car tire can cause excess wear.
With a race tire, these issues take a back seat to getting the entire contact patch on the racetrack. Under-inflation of a race tire results in only the inside and outside edges of the contact patch doing most of the work while the center of the contact patch is under-worked. Conversely, when a race tire is over-inflated, the center of the contact patch is worked harder than the inside and outside edges (this condition is called “crowning”). In both cases, maximum grip is not achieved because the whole contact patch is not being use effectively.
Once an acceptable tire pressure is determined, slight changes can have a positive effect on the performance of the tire.
One may wonder how a race team determines optimal tire pressures. The most effective method is to measure tire temperatures. However, that concept is worthy of its own installment of our race car technical discussion, so we’ll cover that another time.
In the coming installments of Supermodified Tech Knowledge, we’ll continue to explore the full use of the tire’s contact patch by looking at camber, toe and stagger.
If you have questions, comments or topics you would like to see covered, you can contact me at motosports@groupRtech.com. Also, You can follow me @groupRmtrsports and submit questions via Twitter as well.
You can also leave your comments and further questions in the comments section below. We’ll pass them along to The Bogwan while he checks his contacts and looks for fresh rubber.