subject: Tires for Dummies: Understanding Tire Codes, Sizes, Load Indexes, and Speed Ratings [print this page] Tires for Dummies: Understanding Tire Codes, Sizes, Load Indexes, and Speed Ratings
As you walk through the door of your local tire shop several things overcome you: the pungent rubber tire smell, the sounds of an Indy 500 custom-built 30,000-rpm lug nut removing wrench, the slight fear of not knowing what in the world you are doing. Luckily, there is a worker half-smiling at you from behind a computer.
The gruff but friendly technician, tells you that it is going to be a while until you can be helped because the tire technicians are unloading a shipment, and suggests you make yourself at home in the waiting room. You plop down next to a stack of outdated magazines and glance around, spotting stale coffee and a small bowl of peppermints, a television set from the 1980s discussing the latest news in a foreign country, and an old Highlight magazine that reminds you of childhood doctor's offices. Nothing is gripping your attention at this tire store, so you look around for something to read to help pass the time.
On the coffee table in front of you is a product catalog, opening the catalog you realize you know absolutely nothing about tires, and for a slight second you regret opening it for fear that you chose the wrong tires and are going to have to deal with them for 40,000 to 60,000 miles depending on your terrain and weather conditions, not to mention the thought of wasted money. Then, to your relief, you see a section describing tires and explaining their codesperhaps you aren't an idiot after all.
Reading through the catalog information pages, you see that each tire has a specific series of codes imprinted on the sidewall of your tire. You read that the original equipment is found on a sticker on the driver's side door jamb or in the owner's manual, and is a series of numbers and letters corresponding to a variety of measurements and specifications related to the individual tire, such as 225/60R16 91H. What do all of those codes correspond to? The first section, 225/60R16 corresponds to the size of the tire. The 225 is the width of the tread in millimeters. The 60 is the aspect ratio of the sidewall, i.e. the sidewall is 60% of the width of the tread. The last number, 16, is the actual diameter of the wheel that would match up with the tire. The numbers following the first set are the load index and speed ratings for the tire. The numbers corresponds to a chart showing the load index at maximum PSI, or how many pounds each tire can withstand, and the letter corresponds to a chart showing the speed ratings, or what speeds the tire can withstand without rupturing. After reading the catalog information pages, you feel more informed about tires in general, but realize that there are hundreds of combinations of numbers and letters and you have no idea how to pick the right ones for your car.
Though there are hundreds of thousands of tire options, and there are probably several that would fit your car, the original equipment tires are the best for everyday situations because they are designed for your vehicle. However, the catalog states that designated winter tires and specialty tires are sufficient for some situations and to talk to a professional about what is the best for your car. The catalog even suggests looking into buying tires online in order to save money and time, and then when the tires arrive you can have them installed at a local car shop.
The technician gets your attention and signals that he is ready for you to make your tire choice. You are feeling confident about your tire options and know more about tires in generalturns out you aren't an idiot after all.
