This morning, a curious emblem in the shape of a horseshoe, lit up on my dashboard. In the next instant, another one crackled to life: a visual of a tiny car with a tinier bar blinking on its port side.
I haven’t had the time to get well-acquainted with my new car. So, I wasn’t sure what it was alerting me to, but I had an inkling of what it could be.
The instrument panels of modern cars—built in the Noughties and later, much like those of modern aircraft, have so many features—though far fewer in number, of course—that it’s hard to know the whole caboodle unless you take the time to sit down and read the manual like it were a college textbook.
My guess was correct. The pair of illuminated diodes was, indeed, the Tire Pressure Monitoring System (T.P.M.S.)—a warning to tell me to pump more air into the tires.
Back home, after I read the relevant section in the Quick Reference Guide, I walked down to my car and looked for what’s called the “Tire and Loading Information” label. I found it without difficulty on the door frame.
A piece of small, but terribly technical decal, it has, among other things, a key combination of numbers and letters, which, when deciphered, like a code, tells you much about the car’s tires. It looks like this: P195/55 R 16 86V
P. The letter “P” denotes that the tire was made for a passenger car.
195. This number, preceding the slash, tells you how wide the tire is under normal pressure, in millimeters. This one is 195 millimeters wide, which works out to 7.67 inches.
55. This number, after the slash, known as the aspect ratio, is a measure of the height of the tire (from the rim to the tread.) This tire’s height is 55 percent of its width, which equates to 107.25 millimeters or 4.2 inches.
The lower the aspect ratio, the more the ability of the car to remain stable when moving, particularly, when turning a corner at high speed—that is, the better is its “road holding,” but a side-effect of that is that it can lead to a less of a comfortable ride.
R. This letter refers to the construction of the tire. “R” refers to a radial structure. The “D,” which stands for a diagonal structure, has now been abandoned and is only to be found on vintage cars.
16. This number, expressed in inches, indicates the diameter of the wheel (a sturdy, circular frame made of metal or alloy) on which the tire (the rubber band that grips the road) is mounted. When getting a new tire, you can’t get one of a different size.
86. This is the Load Index. It lets you know the amount of weight that an individual tire can safely bear. 86 stands for 1,168 pounds at maximum air pressure.
Multiply that by four tires to get your car’s maximum load capacity, which in this case is 4,572 pounds. But there’s a catch. Even though the tires can, in theory, support a lot of weight, the “combined weight of occupants and cargo” of this car “should never exceed 848 pounds.” Even so, never install tires with a lower load-carrying capacity than the original tires that the factory installed on your vehicle.
V. This letter indicates the Speed Rating—that is, the maximum speed for which a tire was made. Each letter corresponds to a certain maximum speed. The lowest rating, typically, found on passenger car tires is “Q,” which means 99 m.p.h. The highest, “Y,” is good for 186 m.p.h. and when enclosed in parenthesis, as in “(93Y),” it means “in excess of” 186 m.p.h.
A “V” rating means that this tire can handle speeds up to 149 m.p.h., which, by the way, is a lot.
I waded through so much knowledge—happily so—without getting to know how much air the tires had lost. But I did learn that the maximum “cold tire pressure” should be 33 PSI or 230 kPa.