All vehicles are supported by a cushion of air contained in four flexible rubber tires. Each tire’s contact patch, or “footprint,” is a little smaller than a hand. As a result, not much of the tire's surface area is touching the ground, so the amount that does touch the ground must handle a great deal of weight (i.e., load) and force. These four patches create the traction which makes the vehicle go, stop and turn. Basically, they send feedback to the driver which helps to control the vehicle.
The contact patch will vary in shape and size depending on the geometry of the tire, and this affects various performance characteristics of the tire. Tires with a higher profile or aspect ratio (i.e., the height of the sidewall is fairly large compared to the width of the tire), like a 65 or 60 ratio, tend to have a long and narrow contact patch. Typically, these would be tires made for passenger cars and light trucks. The longer, narrower contact patch gives these tires a smooth ride and allows them to handle in a predictable manner. They may also have especially good traction in snowy conditions.
Conversely, most high-performance and ultra-high performance tires have a lower profile (i.e., lower aspect ratio), like a 45, 40 or 35 ratio. As a result, the contact patch is generally shorter and wider, which gives them strong cornering stability and traction. This allows high-performance and ultra-high performance vehicles, like the Challenger, to have very responsive handling, especially on dry roads.
Low Profile 275/40-20
Low Profile 275/40-20
Since the contact patch is the only connection point between your vehicle and the road, its size and shape play a pivotal role in your vehicle's performance. The design of the contact patch is an engineering feat that is specific not only to each manufacturer, but for each individual tire. The design of the contact patch can affect traction, handling, and treadwear.
Many variables affect the contact patch and the results it provides. The most critical factors for drivers to be aware of are vehicle load and air pressure. A tire's maximum operating pressure will be molded onto the sidewall of the tire. However, it is recommended that tire air pressure be set to the vehicle manufacturer's specifications, generally found on a placard on the door panel.
For performance vehicles, wider tires are used. This does not necessarily increase the size of the contact patch, but rather, changes its surface shape. This reshaping of the contact patch makes it more efficient for accelerating, braking, and handling. In some cases, certain performance vehicles will utilize a staggered tire fitment. A staggered tire fitment, or staggered tire application, is the use of wider tires on the rear of the vehicle and narrower tires on the front. While this practice is often adopted for cosmetic purposes, it is recommended for performance purposes only. When the 2008 Challenger debuted, it came with Goodyear F1 Eagle 245/45-20 tires on the front and 255/45-20 tires on the rear.
A staggered tire fitment should only be used when the rear axle is heavier or when the vehicle is rear-wheel drive. In either of these scenarios, handling issues can occur. The staggered fitment is one solution. For vehicles with a weightier rear, the wider contact patch on the heavier end will generate neutral handling behavior. If a vehicle is rear-wheel drive, even with an even weight ratio, the drive axle can apply additional forces on the tires, which will lead to handling issues. Having a wider, shorter tire contact patch on the back end will allow for more traction under acceleration than a non-staggered fitment.
If you want to know the size of the contact patch of your tires, there is an easy way to determine this. Simply jack up your vehicle, put fingerprint ink on the bottom of the tire and then let the vehicle down, while someone else is keeping his foot on the brake (to prevent the tire from rolling). The tire will leave a mark on the paper that represents the tire contact patch, or “footprint.” (Note- The paper should be outline paper divided in one inch blocks, it makes measuring the contact patch easier).
Once done, you will have a “picture” of the tire contact patch, and can easily measure its size in square inches (width of the patch times the height of the patch). If you take that number multiply it by four, you can determine how much rubber is on the road. As an example, a P225/60-16 tire, with 32 PSI, will have a 36.75 contact patch (see image, below), and all four tires will have a static contact area of 147 square inches of rubber touching the road.