To get the maximum benefit from a vehicle's tires, two things need to be monitored - tire inflation pressure and tire tread wear.

Tire Inflation
Every vehicle has a factory-recommended inflation level, depending on if the tire is mounted on the front or rear axle. The factory-recommended tire pressure can typically be found on the placard located on the inside of the driver’s door jamb. Note: The tire pressure found on the sidewall of the tire is the maximum inflation that tire can support; in most cases this is not the proper inflation for the vehicle.

Changes to tire pressure can occur as outside air temperatures fluctuate in locales where seasonal changes are extreme, such as the upper Midwest. A simple-to-use tire gauge is the best tool to determine if air should be added or - in some cases - subtracted. In order to get the most accurate reading, tire pressure should be measured and adjusted while the tires are cool from sitting at least three hours or overnight.

Tire inflation pressure should be checked at least once a month. On average, for every 10-degree (F.) drop in the surrounding air temperature, you could lose one pound of air pressure in a single tire. Given that, it's easy to see how a fifty-degree swing in air temperature could affect how well your vehicle will handle and perhaps even compromise safety.

Tread depth
Tread depth is important because tread gives tires their ability to evacuate water and grip snow and/or ice. The shallower the tread depth, the greater the chance of hydroplaning on wet roads or slippage on snow and ice, both of which situations may result in loss of control.

Here is some additional information regarding tires: 

Q	When buying only two tires for a front-wheel drive vehicle, why should they be mounted on the rear axle instead of the front?
A	Because a vehicle with brand-new tires on the front axle and worn tires on the rear has a greater tendency to lose control when turning in wet or slippery conditions. While the new tires on the front may “hug the turn,” the worn tires on the rear may slide out and “fishtail.” This condition is known as oversteer, and it has been known to cause serious and fatal accidents.
Q	Why should four winter/snow tires be installed instead of two on the drive axle?
A	The TIA (Tire Industry Association) recommends installing winter/snow tires on all four wheel positions. This is to avoid the difference in traction qualities when cornering which could result in adverse handling characteristics leading to loss of vehicle control. In order to maintain performance and stability, winter/snow tires should be installed on all four wheel positions. Why even have winter tires?  It's a fact: as temperatures drop below 45-degrees, the rubber compound in an all-season tire becomes harder and loses its ability to grip the road. The rubber compound in a winter tire is designed to remain soft and pliable, providing superb traction. All-season and winter tires are about as similar as sandals and snowshoes.
Q	Why is it important to follow the size, load index and speed rating on the placard when selecting replacement tires?
A	Every new vehicle is engineered to deliver maximum performance. The tire specifications on the placard are directly tied to the suspension and braking system on the vehicle. If a different size or lower speed rating than the one indicated on the placard is used when the original tires are replaced, the responsiveness and handling of the vehicle may be affected. If the load index on the replacement tire is lower than the one on the placard, the tire may not be able to carry the maximum weight of the vehicle.