Your tires support the weight of your vehicle, right? Well, actually they don’t. It’s the air pressure inside them that actually supports the weight. Maintaining sufficient air pressure is required if your tires are to provide all of the handling, traction and durability of which they are capable.
Don’t have the mindset of setting tire pressure…and then forget about it! Tire pressure has to be checked periodically to assure that the influences of time, changes in ambient temperatures or a small tread puncture have not caused it to change.
The tire pressure recommended in your vehicle’s owner’s manual or tire information placard is the vehicle’s recommended cold tire inflation pressure. This means that it should be checked in the morning before you drive more than a few miles, or before rising ambient temperatures or the sun’s radiant heat affects it.
Since air is a gas, it expands when heated and contracts when cooled. This makes fall and early winter months the most critical times to check inflation pressures…days are getting shorter…ambient temperatures are getting colder…and your tires’ inflation pressure is going down!
The rule of thumb is for every 10° Fahrenheit change in air temperature, your tire’s inflation pressure will change by about 1 psi (up with higher temperatures and down with lower).
In most parts of North America, the difference between average summer and winter temperatures is about -50° Fahrenheit…which results in a potential loss of about 5 psi as winter’s temperatures set in. And a 5 psi loss is enough to sacrifice handling, traction, and durability!
Additionally, the difference between cold nighttime temperatures and hot daytime temperatures in most parts of the country is about 20° Fahrenheit. This means that after setting tire pressures first thing in the morning, the vehicle’s tire pressures will be almost 2 psi higher when measured in the afternoon (if the vehicle was parked in the shade). While that is expected, the problem is when you set your vehicle’s tire pressures in the heat of the day, their cold pressures will probably be 2 psi low the following morning.
And finally, if the vehicle is parked in the sun, the sun’s radiant heat will artificially and temporarily increase tire pressures.
It’s important to remember that your vehicle’s recommended tire pressure is its cold tire inflation pressure. It should be checked in the morning before you drive more than a few miles, or before rising ambient temperatures or the sun’s radiant heat affects it.