We all have to do our best to make sure our vehicles stay in one piece. We check the oil, we top off the coolant, and yes, we observe the tire pressure. The last of these is an easy but important one, and to learn more on why, we spoke with Firestone’s Keith Willcome.
We started by asking: what makes inflation an important topic to begin with? “A tire is basically a pneumatic device,” said Willcome. “The tire’s structure itself supports a small part of the load, but the air pressure inside the tire is what supports the vast majority of it.”
Running on an underinflated tire has negative effects on a its integrity, as Willcome explained. “When you drop the inflation pressure, the amount of flex in a tire goes up,” he stated. “That generates a lot of heat from internal friction, much like bending a coat hanger over and over until it breaks. The heat is really what destroys the tire.”
Another aspect that pertains to tire pressure is the tire’s ability to react to outside forces and elements. “Potholes, rain, steering input, braking and traction are all affected by tire pressure,” said Willcome. “The tire cannot transmit these things to the car well, unless it has the proper inflation to stabilize its structure.”
Just as steering has understeer and oversteer, tires have underinflation and overinflation. Underinflation, as Willcome explained, forces the tire to flex more than it ought to, as well as flex in places not designed for flexing. “It changes the stress locations in the tire, and generates all of that excessive heat,” said Willcome.
The flipside, overinflation, has its own downsides. “Overinflation has several effects,” said Willcome. “One of them is that it changes the shape of the tire, kind of like a balloon. The belts are not able to hold the shoulders down, so you end up running on the center of the tire. This can cause the tire to bounce over bumps, instead of absorbing them.”
Both overinflation and underinflation tie into the factor of the contact patch, which is the area of the tire that is in contact with the ground. The former causes the middle of the tire to be in contact, while the latter causes the sides to be in contact; ideally, the tires should have an even contact patch across both the sides and the middle, the better to inhibit slipping and also promote tread life.
So how does one choose the correct tire pressure? “Go by what is on the door code, or what is in the owner’s manual,” said Willcome. “That psi number is what the vehicle manufacturer recommends, and they choose that pressure based on not only the load carrying capacity of the vehicle, but also the vehicle’s optimal handling characteristics.”
This weekend, take a moment to bust out the tire pressure gauge and look to see if all of your tires are running on the correct psi. You can also head on over to the Firestone website to see some of the company’s latest offerings for cars, trucks, and more.