Doug McAllister/Under the Hood: Heat changes tire pressure

Q. I put air in my tires yesterday and had all the tires at the same pressure. My question is that if the tires are in direct sunlight, will that increase tire pressure? I have two tires that were in the shade and two tires in the sun. The tires that were in the shade were the same pressure that I had filled them up with. The two tires in the shade were 1½ pounds heavier. Is that because of the sun hitting the tires?

A. Temperature has a big affect on the air pressure in tires, so what happened to you makes sense. The sun heated up the tires on that side of the car and the tire pressure went up. When you check the tire pressure you always want to set it first thing in the morning to the cold tire pressure, as the day warms up the tire pressure will go up.

Tires have to be checked periodically, especially when we go through a change of season, which we’ll be doing soon. As colder weather sets in, you could see the tire pressure drop by as much as 5 pounds per square inch.

Don’t forget, low tire pressure is a big drag on fuel economy, so it’s good that you are keeping them set properly.

Fall maintenance

It may be starting to cool down a little as we head into the fall season, but that means things will be heating up on the roads in terms of more traffic. Make sure to pay attention for more activity from student drivers, buses and pedestrian traffic.

It’s also a good time to pay attention to unperformed maintenance on your own car or truck. Be sure that all lights are operational as well as mirrors for proper visibility. This hot summer may have taken a toll on other components of your vehicle so be sure to have a shop inspection as we head toward winter.

Check the spare

When was the last time you checked your spare tire, or checked to see if the jack and lug wrench is in the car and if it works. You would not want to find out that the tire is flat or the jack is missing the day you need it. Preventive maintenance will always save you time and money in the long run.

Ÿ Douglas Automotive is at 312 S. Hager Ave., Barrington, (847) 381-0454, and 7218B Virginia Road, Crystal Lake, (815) 356-0440. For information, visit douglasautomotive.com. Send questions to underthehood@dailyherald.com.