Tire Pressures

We all know how important maintaining proper tire pressure is. Tire pressures affect safety, grip, and tire wear. Tire pressures are affected by temperature, both the ambient temperature, and the actual tire temperature. Normal highway driving causes tires to heat up, and causes pressures to increase. Track days and autocross events produce a lot more heat so what can we do the minimize the increase in pressure


Pressures change because of the air and moisture that is in a tire. The moisture in a tire affects the pressure more than the air alone. Air and moisture in a tire have a greater affect on tires that get very hot because of spirited driving, auto crossing, or road racing. A tire with a pressure of thirty psi will increase in pressure as much as ten to fifteen psi when tire temps go above one hundred fifty degrees. This increase in tire pressure changes the cars handling, grip, tire wear, and frustrates the driver. Racers will start with lower than desirable pressures with cold tires, hoping to guess at how much the tires will increase in pressure as the tire heats up. Different track conditions each week results in a car that under steers one week and overseers the next. A car that under steers results in the front outside tire getting over heated, this causes that tire pressure to increase more than normal, which results in more under steer. In other words the problem progressively gets worse.

Racers usually inflate their tires with nitrogen rather than air. ( If they aren't they should be) This is because compressed air is usually at 100% relative humidity. (Think about the water that accumulates in an air compressor tank and in the air hoses) Nitrogen usually contains about 1% relative humidity, a huge improvement.

There's still a problem though, when nitrogen is usually added, it is added to a tire at zero psi, and a tire at zero psi is full of air and moisture. The better method of inflating with nitrogen is to use a "Tire Evacuator", a tool that evacuates the tire of air and moisture before adding the nitrogen. This will result in the smallest tire pressure change, with temperature increases. When a tire pressure changes less, the tire becomes more predictable, and so does the cars handling characteristics.

A "Tire Evacuator" is a tool that connects to the end of a normal air (nitrogen cylinder )hose. It uses compressed air or nitrogen pressure to evacuate a tire of most of the air and moisture in the tire. The tire is in a vacuum when nitrogen is added. The "Tire Evacuator" tool requires no electrical power, has no moving parts, and only compressed air and /or nitrogen is required to operate it. This allows it to be used easily at the track. A "Tire Evacuator" uses very little nitrogen to operate; only about one cfm per tire is consumed to evacuate each tire. One cylinder of nitrogen will last to evacuate and fill about twenty tires.

Nitrogen is not expensive to use, most gas suppliers will charge a one year cylinder rental fee of about $ 40.00, and about $14.00 to fill the cylinder. If you are road racing, auto crossing, or just want your car to handle better, be more predicable, and have less tire wear, using nitrogen is the way to go.