Hit the Road with the Right Tires: How to Understand and Buy Car Tires
Have you ever spent a few moments trying to decipher the gibberish stamped into the sidewalls of tires? While most of us have a vague idea about what some of those numbers and letters represent, there is a world of additional information that you can glean from a careful examination. We've broken down the foreign language of tire-buying to help those with flat tires and worn out treads find the best tires for the money.
Suppose we start by writing down all the information on a tire from this author's Volvo:
- M+S P225 55 R16 94V radial tubeless
- Maximum load rating 670 kg (1,477 lbs.)
- Max permissible inflation rating 300 KPA (44 psi)
- Tread 4 plies: 1 polyester, 2 steel, 1 nylon. Sidewall 1 ply polyester
- DOT LMT4 3LL 2310
- Standard load
- Treadwear 400
- Traction A
- Temperature A
How to Read a Tire
M+S: means mud and snow; in other words, this all-season tire should perform well in mud and snow.
P225: P means passenger car. If this were a light truck, this code would be LT; ST for a special trailer; or T for space-saver spares. 225 is the width in millimeters of the tire at its widest point, perpendicular to the diameter of the tire. (If this were a shoe, it would be your width; in my case, E.) In other words, the higher this number, the wider the tire. This is part of what determines the footprint of your tire, or how much tire is in contact with the road at any given time, which in turn helps determine how stable your car is at speed.
55: 55 is a tricky number to derive. It is a percentage: the ratio between the width of the tire and its sidewall height. Those ultra- low-profile tires so popular today that appear to be flat but aren't will have a lower number here, such as 35, as their sidewalls are so short.
R16: R: The R means this is a radial tire. This refers to the way the tire is assembled, layer by layer. In a radial tire, the core of the tire is laid out across the tire, rather than in the direction of the tread. 16: The diameter of the wheel in inches that the tire will fit. The wheel is measured where the bead of the tire rests, and can only me measured sans tire.
94V: 94 is a measurement of the tire's load index, or how much weight each tire can support. This number is not required by law to appear on all tires (it is included elsewhere on your tire sidewall). A 94 will support 1,477 pounds. V is a speed rating, or the maximum speed tires are designed to be driven for extended periods. Any V-rated tire will perform well while traveling at 149 miles per hour for an extended time — certainly fast enough for this writer. A Y-rated tire can run at 186 mph, not counting the time spent pulled over while the cop writes out a speeding ticket.
Radial Tubeless: As explained earlier, this is a radial tire, and does not use an inner tube.
Maximum Load Rating 670 kg (1,477 lbs.): This duplicates earlier information. This rating is per tire, so four such tires would carry a maximum load of around 6,000 pounds. The curb weight of the Volvo is 3,600 lbs, so I could comfortably carry an extra 2,400 pounds and my tires should still perform well. (My miles per gallon, however, might be pretty bleak.)
Max Permissible Inflation Rating 300 KPA (44 psi): Keep an eye on maximum tire pressure; over-inflating can seriously degrade the grip tires have on the road. Remember that air expands when heated, so tire pressure will increase while driving, especially in hot weather. Follow the guidelines in your car's manual for maximum inflation pressure.
Tread 4 Plies: 1 Polyester, 2 Steel, 1 Nylon. Sidewall 1 Ply Polyester: Tires are built up of different layers running different directions, like muscles on your torso. Your sidewall will tell you just what those layers are made of, such as in this example.
DOT: These letters, standing for Department of Transportation, show that the tire meets U.S. standards.
3LL: This group of characters is code for the manufacturer of the tire; in this case, Uniroyal.
2310: These four characters show the week and year in which the tire was manufactured. Ideally, the newer the tire, the better.
Standard Load: This means just what it says. If the tire was made for heavy loads or light loads, those words might appear on the sidewall.
Treadwear 400: This indicates the tire's wear rate as determined by DOT tests. The higher the number, the longer a tire should last, depending, of course, on your driving habits. A 400 should last four times as long as a tire rated 100. If you like to peel out from stoplights, though, you'll pay the price in more frequent tire changes.
Traction A: This is a measurement of how quickly the car will brake on wet pavement. In this case, an A is not the top grade: AA is best. C is the lowest.
Temperature A: This shows a tire's ability to stand up to heat. An A here is the top grade, and should be least affected by high temperatures. Again, C is the lowest grade.
Which Tire Is Best for You?
Knowing all of this, how can you match your tire purchase to your driving habits?
First, consider your climate. Do you deal with the scorching heat of Phoenix or the breathtaking cold of Winnipeg? Choose a tire that functions well in those conditions. Second, consider your driving habits. Do you push the envelope on speed? Choose a tire that will help you keep the car under control; that is, one with better traction. Third, consider aesthetics. If you really like the low-profile look, shop for a tire with a low profile rating, but know that you're buying yourself a rougher ride when you do so.
And of course, the best tire for the money may not hit all your requirements on the head, but a general-purpose all-season radial could be the cheapest option, thanks to the volume demand. As a corollary to this, keep a sharp eye peeled for promotions like Goodyear Tires on sale from Walmart and rebates from TireRack.