By Walter Hamill
Picture this. It’s a brisk fall morning, and and you’ve overslept a few minutes, because let’s face it, the bed is warmer than the air outside. You rush through your morning routine. When you finally get into your car, you are greeted by an ominous warning on your dash: Low Tire Pressure. You get out and walk around the car checking your tires to see if they look low. But they look fine, so you take the risk and drive to work, wondering if you are about to experience a flat tire. Later that day, you get in the car to go to lunch and the light is out. All is forgiven, and you promptly forget about it…until the next time it happens.
What is happening?
Sound familiar? If it does, don’t worry. You are not alone. It happens to millions of people every day, most often when we get the first hint of a fall chill in the morning air. In 2005 automakers began installing tire pressure monitoring systems on new cars. By 2012, all passenger cars sold in the U.S. were required to have a tire pressure monitoring system. Most cars use a sensor mounted inside the wheel to monitor pressure. When air pressure inside a tire drops by a predetermined amount the light comes on , and stays on, until the pressure is corrected.
Why does it happen in the fall?
The tire pressure light can, and will, come on anytime the pressure falls below the threshold set at the factory. There are many reasons for a tire to lose pressure. Punctures, leaky valve stems, and poor sealing at the bead just to name a few. There is also a certain amount of air that is lost directly through the rubber itself, but by far the most common cause of pressure loss is the contraction of the air due to cold weather. The air in your tire is comprised of many elements, including water, which has a tendency to expand and contract with temperature changes. When it gets cold, the air inside your tire contracts and the warning light comes on. The tire can lose up to a pound for every 10 degrees of temperature change. Friction caused by driving, as well as afternoon heating, can frequently return the air in tires to enough of its original density that the light turns off, making the problem go away. For now…
Why should I care?
In the days before tire pressure monitors, many of us went about our normal lives completely unaware of what was happening without repercussions. Should knowing suddenly make us take notice? Absolutely. Properly inflated tires handle better, last longer, and reduce the risk of spontaneous failure. Oh, it saves money on gas too!
Why do my tires have green or blue caps?
In the mid 2000s filling tires with nitrogen got very popular. Nitrogen is a popular and inexpensive alternative to air with some additional benefits. Nitrogen is dryer than air, reducing the impact water has on inflation. Nitrogen is also bigger at a molecular level. This fact reduces the amount of gas lost to microscopic leaks. The bottom line is that nitrogen is more stable than the air we breathe, and many people feel it is a better choice for filling tires. When a shop fills tires with nitrogen they will typically replace the valve caps with ones that are green or blue. This is to let the next person filling your tires know what is in them. Mixing air and nitrogen is perfectly safe, but doing so dilutes the nitrogen and offsets the benefits.
Don’t throw away your tire gauge
Now that you have a tire pressure monitor, and maybe even nitrogen, in your tires, do you still need a tire pressure gauge? Yes you do. Checking your tire pressures periodically can help you stay ahead of a low tire light coming on. While doing so, why not take a minute and look at the tread too? Try the Lincoln penny test. Simply insert a penny in your tire tread, upside down. If you can see the top of Lincoln’s hair it means there is not enough tread depth left, and it is time for a new tire.
Tire pressure affects handling and braking, critical factors to a safe trip. Properly inflated tires last longer and are much safer. Plus, it’s estimated that under-inflated tires waste 2 billion gallons of gasoline every year. So do yourself and your wallet a favor by checking your tire pressure often, especially in the fall.
Featured image by Przemek P.