Putting all political posturing aside, it’s foolish to downplay the importance of proper tire pressure. Simply put, a properly inflated set of tires allow a vehicle to operate as it was designed. When one or more tires are under-inflated, performance is negatively effected; the vehicle’s ride and handling will suffer, along with its gas mileage.
The term “where the rubber meets the road” directly applies to this issue. A properly inflated tire provides the optimum contact patch (the section of rubber that touches the road surface). An under-inflated tire, on the other hand, has a larger contact patch with increased rolling resistance. More friction where the rubber meets the road means your engine has to work harder, thus lowering fuel efficiency.
Straight line friction’s just part of the equation. Poor handling is an even larger culprit.
When driving for optimum fuel economy, you need to pay particular attention to braking. The more you’re on the brakes, the more fuel your vehicle is consuming. When your tires are under-inflated, and your vehicle isn’t handling as well as it should, you’re more likely to be reliant on the brakes when entering a turn. When your tires are properly inflated, and you’re confident in your vehicle’s cornering capability, you’re more apt to carry inertia through a curve, scrubbing off speed with the tires.
The less energy your vehicle uses when exiting the curve, more more fuel you’ll save.
Periodically checking your tire pressure is an essential, yet no-cost step in achieving optimal fuel economy. You should invest in a quality tire pressure gauge, as the most inexpensive gauges can produce inaccurate results. Whether you go with a fancy digital or a traditional analog unit, a gauge with an integrated bleeder valve helps you fly through the task. Keep one in the glove box and you’ll never go wanting when you’re out on the road. A home or portable air compressor can come in handy, as well.
An increasing number of vehicles provide advanced electronic tire pressure monitoring systems as standard or optional equipment. These systems provide real-time feedback on the pressure in each tire and are most likely to be found in luxury and hybrid vehicles. Although aftermarket tire pressure monitoring systems are available, they’re most likely to be found on large trucks, recreational vehicles, campers, and trailers.
Resource: Car Talk
Having the correct tire pressure is extremely important for getting good gas mileage and the most life out of your tires. Your car has a specific tire pressure that will give the best gas mileage, handling and tire life for that car, and it’s written right on the door of the car. That’s the one you should follow when filling up.
Over-inflating your tires will give you a bouncy ride and an ill-handling car, while under-inflated tires can develop premature wear from increased friction. Either way, not having your tires at their recommended pressure will negatively affect tire wear and vehicle performance.