The Accord Contact Patch
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 2 lb rabbit or a 100 lb 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? Was it just a close call, or is there something behind the car lying 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"? It's one of the most misunderstood words about cars. And the contact patch idea is very simple.
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. Without a contact patch, you are not going anywhere.
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 100 sq-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 one your hand prints.So your contact patch is very small compared to the area of the car.
This contact patch 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 contact patch you have, the better you apply the thrust the car has against the road surface to accelerate, brake or corner the vehicle. When you hear about racing terms such as "oversteer" and "understeer" they are referring to how well the rubber of the tire grips the road and what happens when that grip starts to slip loose from the road surface. Typically the contact patch of either the rear or the front end of the car breaks loose before the opposite end.
What is harder to understand is that the contact patch does not remain constant while you drive. Go around a curve and the tires will not have the same shape or amount of contact patch as when the car is standing still. Hit a big bump and your contact patch may vanish. No patch means no control.
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?
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