A tire-pressure gauge is a pressure gauge used to measure the pressure of tires on a vehicle.

Keep Your Tires Properly Inflated
Under inflated tires require more energy to roll, which translates into more frequent fill-ups. You can improve your fuel economy by about 3.3 percent if you keep your tires inflated properly, according to the DOE. The psi number noted on the sidewall of your tires is the maximum pressure of the tire and is not the proper inflation level for your car. Your vehicle manufacturer will list the recommended tire pressure in your owner's manual or a sticker on the doorjamb of the driver-side door. Buy a tire-pressure gauge and check your tires monthly, adding air as necessary.


Let's say your tires are supposed to be filled to 35 psi. If they are filled correctly, six square inches of your tire are touching the road, just the way your tires were designed. But let some air out, and now the pressure is only 30 psi. Since your tire is like a balloon, the more air you have on the inside, the rounder and more firm your tire becomes. If you had six square inches touching the road at 35 psi, the flatter 30 psi tire will have eight square inches touching at once, making it harder for your engine to get things rolling from a dead stop.


Tires should be properly inflated at all times. Insufficient air pressure will not only reduce your mileage but also cause your tires to wear out prematurely. Keeping air pressure higher will yield better mileage albeit with a harder ride (don’t over-inflate or you’ll also wear out your tires prematurely).

In addition to tire pressure, make sure your wheels are balanced and aligned.

Not as well known is that tire tread can also make a big difference. Rolling resistance is the keyword here.

Environmental conditions can introduce a 13% to 15% variability in pressure due to temperature (0 °C to 40 °C), and additional changes can result due to altitude. Most car owner manuals do not state rated pressure as a function of temperature or altitude and leave it to the user to make appropriate measurements.

Since tires are rated for specific loads at certain pressure, it is important to keep the pressure of the tire at the optimal amount. Tires are rated for their optimal pressure when cold, meaning before the tire has been driven on for the day and allowed to heat up, which ultimately changes the internal pressure of the tire due to the expansion of gasses. The accuracy of a typical mechanical gauge as shown is +/- 3 PSI. Higher accuracy gauges with +/- 1 PSI accuracy can also be obtained.


Regulations on tire pressure

By September 2007 all new automobiles below 10,000 pounds sold in the United States will be required to incorporate a direct pressure measurement for each tire. The driver must be notified if any tire is underflated by 25% or more than the rated placard tire pressure.