Drivers will keep their tire pressure in optimum parameters, and make sure that the threads are still good, but most often than not, we overlook the other factor that tells us how good the tire is at holding the car on the road, its freshness.
As tires are made of rubber compound, and rubber tends to get stiffen over time, fresher tire will always yield better grips. As a rule of thumb, never buy tires that are manufactured more than 6 years ago, sitting on the shelves all these while.
Fortunately, the tire manufacture date is stamped on every tire as part of the DOT code. Look out for the 4 digit code (if it is 3 digit, your tire is already way too old, manufactured before the year 2000) stamped on the sidewall of the tire. The first two digits denote the week of birth, and the last two digits describing the year of birth.
In the accompanying picture, then, 3902 means this particular tire was manufactured on the 39th week of 2002. Dividing 39 by 4 (4 weeks a month) gets us 9.x, so it was produced sometimes in September, 2002. Simple as that.
So, next time when you put in new tires, make sure they are still new. If your current set of tires still has good threads left but are already over 6 years since it was produced, consider replacing them.
More info can be found on wikipedia Tire Code
Many drivers, while familiar with the size of engines and familiar with the need or regular services and oil change, are completely unaware of the importance of the patch of rubber that is between the car and the road, the tires.
Car tires come in various sizes and profile, to know what they are is to learn how to read the side markings. Together with the brand and product name, there is always a standard row of numbers and letters describing the size and profile of the tire, like in this picture: 205/65R15
- 205 denotes width in of tire in millimeter, in this case, 205mm.
- 65 denotes the aspect ratio, which is the height of the side wall of the tire. 65 basically means it is 65% of the width of tire, in this case, the wall of the tire is 133.25mm tall.
- R means the tire is of Radial construction, true to pretty much all modern road cars. The other type is cross-ply construction, mostly only found in vintage cars.
- 15 is the size of the wheel rim the tire fits, in inches.
Performance cars usually have a smaller aspect ratio as well as wider tires for better handling around the corners. To allow this and yet keep the overall circumference, bigger rims are needed.
On tire pressure:
Most sedan car tires work well at around 29-31 psi, or around 200 to 210 pascal. For optimal performance and fuel economy (low pressure = increase fuel consumption, high pressure = less grip), check your vehicle manual for optimal tire pressure. The information can also usually found at the body of the car where the driver door closes, or at the inside of the driver door itself.