There’s a popular theory among auto maintenance do-it-yourselfers that overinflating your tires will improve your fuel mileage on a long highway trip. Since low tire pressure lowers your fuel mileage and higher psi leads to lower rolling resistance, the theory may even sound true to you. There is only one problem: increased fuel consumption due to overinflated tires is a complete myth.
Should you check your tires before a road trip?
Double checking your tire pressure is an essential part of preparing for your road trip. Every pound per square inch (1 psi) your tires run low will cost you a 0.4% drop in gas mileage. You can’t afford not to check your tire pressure before a long trip.
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Check the plate inside the driver’s side door of your car. This door tag lists important specifications such as the car manufacturer’s recommended tire size and tire psi.
Then take your vehicle to a service station with an air compressor to fill your tires. Set the compressor to your recommended psi and let it adjust your tires. Alternatively, you can purchase your own tire pressure gauge. This way you can check your tires before your trip and continue to monitor them during.
Does overinflating your tires improve your fuel mileage?
You may have heard that inflating your tires well beyond your manufacturer’s recommended psi will improve your fuel mileage. But this is actually a myth that could put you and your passengers at risk.
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Underinflated tires flex more as you drive. This means more of the rubber in the tire touches the road and this extra traction improves braking and acceleration. For this reason, drag racers and serious off-roaders often “air” their tires.
But at the same time, under-inflated tires create more rolling resistance and hurt fuel economy. It may seem true that overinflating your tires further decreases rolling resistance and thus improves fuel economy even more. But the truth is that the tire pressure recommended by car manufacturers is the best psi possible.
The experts at Popular Mechanics actually put this myth to the test. They did the same road trip twice with the same car. During a trip, PM inflated the tires to the recommended 32 psi. On the other trip, the publication ran all four tires at 45 psi.
What was the result ? The vehicle has exactly the same mileage. Overinflated tires may have returned a 0.05 mpg increase. But the cost could have been deadly.
Are overinflated tires dangerous?
The sidewall of your tire has a maximum recommended psi. This can be much higher than the vehicle manufacturer’s suggested pressure and can be a tempting psi to run. But overinflating your tires leads to dangerous driving and an uncomfortable ride.
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When Popular Mechanics tested fuel economy by taking a long road trip in a car with its tires at 45 psi, it gathered some sobering information. First, any increase in fuel consumption was between negligible and non-existent. Second, the overinflation inhibited the car’s handling.
Because overinflated tires don’t flex as they roll, far less of their rubber touches the road than their engineers intended. This has a negative impact on acceleration as well as braking. But in addition, car manufacturers expect tires to act as shock absorbers. Popular Mechanics reported that at 45 psi, his tires caused such a bumpy ride on the highway that his garage door opener fell out of the sun visor where it had been cut.
Overinflating tires does little for fuel consumption and has a negative impact on car dynamics. If there was a “free” way to get much better fuel mileage, don’t you think automakers looking for a competitive edge would have figured it out?
Then read how to upgrade your tire changing tools or see how to prepare your car for a road trip in the video below:
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