Keeping up with tire pressure is relatively easy to do, but many drivers don't take the time to ensure their tires are properly inflated. Not only do tires play a key role in performance, including fuel economy, but it is also dangerous to drive on under-inflated tires - as this is ultimately the leading cause of flats while driving.

After the Firestone recall scandal in the 1990s, the government required that tire-pressure monitoring systems (TPMS) be installed on all new vehicles. However, this did not take affect until 2007, meaning that there are many drivers on the road without these systems, which provide real-time information about the pressure in each tire and alert drivers when one may be getting low.

Fortunately, drivers with older vehicles have solutions. You can obviously check your tires manually from time to time and make sure that you frequently fill them with air. However, there are also aftermarket TPMS products that could also be useful.

There are two types of systems available - direct and indirect. Indirect systems do not technically qualify with government regulations, but most agree that they work and they are free to be sold as aftermarket parts. These devices essentially estimate the pressure left by sensing things such as the relative angle of the vehicle, operating under the theory that wheels will be slightly smaller and flatter with less pressure.

Some devices also use other means of determining the tire pressure, with varying results. Be sure you check into the individual system you are considering to determine exactly how it works. When using these systems, they also have to be calibrated to the "correct" tire pressure. This means you should only install them after you have inflated the tires to their recommended levels. If you calibrate the device when the tire is under or overinflated, the calculations will be off it will not alert the driver at the correct times.

More common are direct systems, which directly attach to each tire and provide real-time updates on the pressure in each of them - a useful tool for motorists who want to ensure their tires are working correctly.

These systems can cost money, but having underinflated tires can actually cost much more over time. The Department of Energy says that for every 1 psi under the recommended level in all four tires, a car loses 0.3 percent of its fuel efficiency - which can definitely add up quickly.