Question: I saw a question that asked “What is the most important control device on a car or vehicle?” but I couldn’t find the answer. What is the most important control device?

Answer: Most people would answer the steering wheel or gas and brake pedals but none of those items are very effective at controlling a car if the tires aren’t in contact with the road. The tires are actually the most important control device on the car.

That portion of the tire that is in contact with the road is known as the tire’s “footprint.” The larger the footprint, the more control you have over the vehicle. If you are speeding, there’s an aerodynamic force on the car that makes the rear end rise up off the road, decreasing the tire’s footprint. If you should encounter a curve or an obstacle in the road, the smaller footprint could cause you to lose control of the car.

When driving on gravel roads, your tire’s footprint is even smaller because it is only in contact with the tips of rocks instead of the solid footprint that would be experienced on a paved road. It’s much easier to lose control of a vehicle on a gravel road so maintaining a lower speed is very important.

In heavy rain where there is standing water on the road, your tires may not be able to squeeze out all the water through the openings in the tread. In this situation, known as “hydroplaning”, the tires can ride up on top of the water like a water ski. In a hydroplaning situation, your tires will lose all contact with the road’s surface and you will lose control of the car. Hydroplaning can start at speeds as low as 35 mph but is more common at speeds above 55 mph. If you see standing water on the road, you should slow and keep a firm grip on the wheel. If you should hydroplane, don’t hit the brakes! Instead, take your foot off the gas and steer the car in the direction you want it to go until the car slows on its own.

It’s also very important to make sure the tires on your vehicle are in good shape and inflated to the proper pressure. If they are bald, they won’t be able to grip the road very well. The best way to tell if your tires are in good shape is to use the penny test. Stick a penny into  the tread of the car. If you can see the top of Lincoln’s head, your tires are worn too low and should be changed.