Dear Car Guy:
A friend of mine recently suggested that I could improve my mileage by over-inflating my tires. With gas prices going up again, I’m thinking about doing it, but I don’t want to make my car unsafe. Got any advice?
Thanks,
Otto Mateck
Dear Otto:
Well, you might get better mileage, but you also might be risking your life. Let me explain why.
Over-inflating decreases the amount of tire tread that contacts the road. Think about it; your tire is rounded, and if too much air is pumped into it, the roundness increases and the tread loses contact with the road. Technically, the tread bulges, so you’ll end up riding in the middle of the tire rather than on the complete surface for which it was designed. Traction is reduced by over-inflation, and road handling can be severely compromised. In the worst case, you can even increase the chances of a high-speed blow-out. Getting the message?
Today’s tires are a highly engineered product, and are meant to be used in accordance with the recommendations of the tire and auto manufacturer. In fact, using the correct, manufacturer specified pressure adds 3+ miles to your mileage performance. Depending upon the model of your car, having the right tires can make a big difference in both mileage and handling.
Think you can tell if your tire is too low just by looking at it? Think again. Tires today are too sophisticated to judge pressure by appearance alone (sounds like dating advice!). Many new tires are designed to bulge somewhat on the side when properly inflated, and this is a characteristic typical of radial tires. What we used to think of as looking a bit “flat” is often perfectly normal. And tires come in different styles, high-wall and low-wall.
So if you can’t tell by looking, how do you know what’s right? Well, like other matters requiring superior technical intelligence, you need to use the right tool. If you’re using one of those “pencil” type tire gauges with the little stick that “pops” out the end, throw it away … it’s junk. The only reliable tire gauges today are a digital or dial-type. Like most hardware, you get what you pay for, and you can expect to pay around thirty bucks for a solid, reliable pressure gauge. Unless you are using your trunk as a storage unit you can easily fit a tire pressure gauge back there. And I hate to tell you, but you can’t rely on the service station air pump gauge either; if it works at all it’s often completely unreliable.
Inside the flap of your gas “door” you’ll often find the recommended tire pressure for your car. Sometimes it’s on the inside of the driver side door jam. These car manufacturer recommendations are based on the weight of your car, and are more accurate and appropriate than what is printed on the tire. This makes sense if you think about it; the weight of the car has a direct bearing on the weight placed on the tires. And you may be driving on tires that are not the original ones that came with your car. So find out what’s right for your car, and don’t just rely on what the guy at the gas station tells you.
Examining the tread and the wear patterns can reveal possible problems and prevent accidents. So, just like your oil (and you can check them at the same time), you should check your tire pressure every 3,000 miles. Your life is on the line … don’t make silly decisions based on saving a few pennies a mile. Follow the recommended tire pressure and please, drive safely.
John Fisher owns and operates Metric Motors located in Sonoma.
