Different tires have different personalities.
It may be hard to imagine that something as mundane as tires can behave in different ways. Most people know that summer tires are stickier than all-season tires, all-season tires provide better grip in cold temperatures than summer tires and winter tires are unbeatable in colder conditions. Digging even deeper, you'll find that depending on things like the type of pavement and weather conditions, the same tire can act in very distinct manners.
But before a tire can corner well, or help with acceleration, or handle precisely, it has one primary job: carry the weight of the vehicle. That is why using the proper tire pressure is so important. A tire that is underinflated or overinflated presents all kinds of problems, such as overheating, premature/uneven wear and poor gas mileage. When underinflated, a tire cannot even perform its primary job. Maintaining and checking tire pressure periodically prolongs tire life and ensures it will perform at its best capabilities.
And it goes beyond a simple visual inspection. An underinflated tire by 10 psi may look exactly like one that's properly inflated. And there's no better way to check tire pressure than using a tire pressure gauge. We sell tire pressure gauges made by Accutire and Intercomp for all needs and budgets. Don't forget to check the pressure when the tires are cold. Pressure fluctuations of 10 psi or more can occur when the tires' temperatures rise.
For everyday driving, Tire Rack recommends following the tire pressure listed for each specific year, make and model. Most, if not all, modern vehicles come equipped with a placard located on the door jamb showing the vehicle's weight and the proper tire inflation, as well as other useful information. As long as the tire size you are running on your vehicle is compatible with the original equipment tire size, you should always obey the recommended tire pressure -- even if you are increasing or decreasing tire size. Finally, when checking and adjusting tire inflation pressures, the "right" inflation pressures are those provided by the vehicle manufacturer, not the maximum inflation pressure branded on the tire's sidewall. The vehicle manufacturer's pressure recommendation can be found on the vehicle's tire information placard label, as well as in the vehicle owner's manual.