What tires are on your car?

Do you know what kind of tires are on your new car? Most consumers don't, even though tires are a critical safety and performance item. All that connects a vehicle to the road are four palm-sized contact patches. Put that way, it's clear that the right tires can make all the difference.

We've found that your new, or nearly new, ride is likely to be shod with performance tires carrying a speed rating of H or higher (above 130 mph), based on a review of how the 2006 CR-tested cars and trucks were equipped. Granted, our snapshot-view of the market may not represent the actual mix of passenger vehicles sold every year, but the 67 models we tested that model year do cover a wide range of vehicles, from small economy cars to ultra-performance sports cars. And, of course, it includes a fair mix of family sedans and SUVs. The good news is that these performance tires deliver crisp handling and better cornering grip at sane speeds. The bad news is that they may wear out at a faster rate than regular all-season tires.

Size matters
Just as the vehicle market proliferates and diversifies, the number of available tire sizes seems to grow. Among the 2006 models surveyed, there were 41 tire sizes; some even require different front and rear tires (called a staggered fitment). Wheel sizes ranged from a small 14 inches for the Hyundai Accent and Kia Rio to a massive 19-inch wheel diameter for sports cars like the Dodge Viper. On wheel size alone, the most common diameter (17 inches) was found on 43 percent of the vehicles, followed by 16-inch wheels at 27 percent. Once common, 14- and 15-inch wheels only accounted for 9 percent of the mix, while once rare 18- and 19-inch wheels account for 21 percent of the 2006 models surveyed.

Go, Speed Racer
Most tires have a speed-rating symbol on the sidewall to indicate the maximum safest speed the tire can be driven. The speed capabilities of most tires are well above legal limits, but higher speed-rated tires generally possess greater levels of handling and cornering grip. Conversely, higher-speed-rated tires generally don't have the all-weather grip or tread wear life of lower-speed-rated tires. S is typically the lowest speed rating found--still good for 112 mph and representing the bulk of the replacement tires on older model cars and trucks. But S-rated tires are a rarity among new vehicles, with only seven percent of 2006 cars and SUVs surveyed being so equipped. Another 12 percent of these vehicles came with slightly higher-speed-rated tires of T, good for 118 mph. We also found that 35 percent of the vehicles came with performance rubber, such as H speed-rated tires (130 mph) and 27 percent came with V-rated tires (149 mph). Ultra-performance tires with an even higher speed rating of Z (above 149 mph, and include W- and Y-rated models) accounted for a significant 18 percent of the 2006 models.

We also found that the speed rating of tires can change with the trim-line of the vehicle. For example, the Honda Civic Hybrid takes an S-rated tire; the Civic EX has an H-rated tire; and the Civic Si comes with a V-rated versions. Maybe an even more extreme example is with the Chevrolet Monte Carlo, where the base LS has an S-rated tire in the P225/60R16 size, but the SS model (tested by CR) came with an ultra-performance P235/50R18 W-rated tires. Replacing the 16-inch tires on the LS will cost about $69 per tire, but replacing the tires on the SS will set you back about $233 per tire--and that's replacing original equipment tire with the same models. The good news is that there's a wide variety of replacement tire models available for many size tires that come on new vehicles. As an example, the 205/55R16 size tire, which came on 15 percent of our 2006 vehicles, was priced from about $60 to $160 depending on tire make, model, and type.

So, you still need to ask yourself: Do you know what's on your car? Or the one you are considering purchasing? Check the information placard found on the car's door jamb.
For more tire information, read "Choosing size & type" and check out the performance ratings for tires that fit your car.

-- Gene Petersen