Contact Patch | The Critical Footprint

Let's image that you are cruising down the highway at 65 miles per hour and suddenly you see an animal jump out in front of your car. Could be a 2lb rabbit or a 100lb plus deer, either way you want to avoid hitting it.

So you yank the wheel to turn the car away from the critter. Did you make it? Just a close call, or is there something behind the car laying in the road?

One of the determining factors that helped decide what just happened is the "contact patch" of your tires. So just what is a "contact patch".

Let's use our imagination again. This time we will image driving our car up a ramp onto a platform made out of very thick glass. Don't worry, its strong enough to hold your car, you and your mother-in-law up in the air.

Now walk under the platform and look up. Do you see where the tires are touching the glass? Well that's the contact patch. The contact patch is that portion of your tire that is in contact with the road surface.

Not too much touching is there? If we looked at a 3,000 car with 30 lbs per square inch of tire pressure it would have about 100sq-in of contact patch. Since there are four tires, each one would have about the area of a 4 x 6 inch index card. Or another way, about the size of your hand print.

This is all that is touching the road, and every maneuver you make with the car is transferred to these small patches of rubber.

The more you have, the better you apply the thrust the car has against the road surface to accelerate, brake or corner the vehicle.

So I hope your tires were in good shape and properly inflated when you encountered the situation we started out with.

By the way, what happened in your mind? Did you miss that poor helpless animal or are you attending a funeral?

More details about cars and their suspension parts later.

(Some information supplied by "Winning - a Race Driver's Handbook" by George A. Anderson.)

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