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.