Tire Selection For Passenger Cars

There are many things to consider when choosing a new tire for your passenger car. Here is a list of some of the important variables to help you make a good choice. All passenger car tires must conform to Federal Safety Requirements.

Six of the variables are listed on the sticker attached to all new tires and cast into the sidewall of all tires.

1. All season rating (AKA: mud and snow rated)
2. Speed rating
3. Manufacture's guarantee
4. Temperature rating
5. Traction rating
6. Tread wear rating
7. Size
8. Name brand

All these variables should factor into the choice of a new tire. Some of the variables are more important than others. Here is a description of each of the variables.

1. All Season - Tires that are All Season rated are marked with the M/S designation on the tire sidewall. M/S (stands for mud and snow) tires are specially designed for traction in wet or slippery conditions. Special tread patterns and rubber compounds are used that maintain pliability in cold weather and minimize the tradeoff between winter grip and dry wear.

2. Speed rating - All tires are assigned a speed rating. The speed rating designates the tires ability to shed heat built up during higher speed operation. In most cases the lowest speed rating is acceptable. How often do you drive over 100 mph for and hour continuously? If you were to run an SR rated tire at speeds over 100 mph for a sustained period the tire would probably fail.

HR= 115 mph
SR= 105 mph
TR= 125 mph
VR= 150 mph
ZR= 180 mph

3. Manufacturers mileage warranties are tricky. The rating is subjective and may not accurately reflect the service the tire will deliver. The warranty is for material defect and does not cover wear from improper inflation or alignment problems. I recommend using the Treadwear rating rather than the manufactures warranty to determine the longevity of a tire.

4. Treadwear - The Treadwear rating (on the sidewall and the new tire sticker) is a number; the larger the number the longer the tire will last. The Treadwear grade is a comparative rating based on the wear rate of the tire when tested under controlled conditions on a specified government test course. For example a tire graded 150 would wear one and a half (1 ¸) times as well on the government course as a tire graded 100. Actual results will vary. A rough interpolation of the numbering system would be:

Under 200=less than 30,000 miles
260= about 30,000 miles
320= about 40,000 miles
360= about 60,000 miles
400= over 60,000 miles
Over 500= about 80,000 miles

5. Traction - The traction grades, from highest to lowest, are AA, A, B, C. This rating represents the tires ability to stop on wet pavement as measured under controlled conditions. A tire marked C traction may have poor traction performance.

6. Temperature - The temperature grades are A (the highest), B, and C, representing the tires resistance to the generation of heat and its ability To dissipate heat when test under controlled conditions. The Speed rating and the Temperature rating are related.

7. Size - How do the size numbers on tires work? what do the numbers mean? All tires have size markings. A generic example would be 195/75 R 14.

Let's take this example of 195/75 R 14.

The "195" is the width of the tire at its widest point that is, at the "bulge"--not at the tread. This measurement is in millimeters.

The "75" number is a percentage. It is referred to as the aspect ratio. The ratio of the width and the height of a tire. The ratio of the distance of the bead of the tire to the ground (the bead is that part of the tire that matches against the rim) over that 195 number (above). So in this case, that ratio is 3:4, or 75 percent. Got it? The tire is 75% as tall as wide. As tires get wider they get taller within the same aspect ratio.

The "14" is the mounting diameter (the size of the hole of the tire). That is, the size rim you'll need for a given tire. Since that 195 number is in millimeters, can you guess what unit of measure is used for this number? It's inches!

The "R," by the way, means that this is a radial tire. Sometimes you'll see "P" or "LT" before all these numbers, which indicates that the tire is designed either for a passenger car or a light truck, respectively.

All cars have tire fitting information stickers. These stickers tell what stock and optional sizes will work on the vehicle. Also proper air pressure settings are provided. The stickers are usually either in the drivers door jamb or the glovebox door. Never mix tire sizes on a vehicle.

8. Name Brand familiarity - Is the tire a National brand? Have you heard of the manufacturer before? It is much easier to warranty a national brand tire like a Michelin, Dunlop, Cooper, Goodyear, Firestone etc. than a Solar, Vixen, Jupiter, Pneumant, or other local or off-brand tires.

To make things even easier, I think that a couple of these variables really have no-brainer choices.

1. In the Northwest everyone should run All Season rated tires.

2. Unless you drive like a maniac, Speed Rating should not be an issue, SR rated tires are fine. Some tire sizes will determine what Speed Rating you are forced to have. Most low profile tires will come with HR or higher Speed Rating.

3. The manufacturer can claim whatever they want for a mileage warranty. Check out the warranty but look at the Treadwear number for a better idea of tire longevity.

So the first three variables that are listed seem to be "givens" to me. Leaving the last four variables as the real decision makers. It's a pretty easy system once you are familiar with how it works. I recommend never buying a tire with ratings less than:

Treadwear - 200 Traction - B Temperature - B

Anything with ratings less than these is getting to be pretty poor quality and tires are not an area to economize. It's amazing how much more quality can be purchased for a few extra dollars per tire. Ideally I would recommend a tire with ratings like:

Treadwear - 360-540 Touring Tire: Traction - A Temperature - B-A
Treadwear - 200-360 Performance Tire: Traction - AA-A Temperature - A

A neat trick for looking at relative value between tires is like unit pricing at the grocery store. Take the Treadwear number and divide it by the cost of the tire. You can compare any tire value by using this method. The results of this division bear a number, the higher the number the lower the per mile cost. This system can be used to compare tires of different cost and Treadwear numbers.

Please don't buy recap tires! I see no value in them. For a few dollars more one can have a real tire. The savings don't justify the risks involved.

When shopping for tires make sure to ask some basic questions:

1. How much is the tire?

2. Does that price include mounting and balancing?

3. If I buy your tires how much is an alignment?

4. Do you rotate and balance your tires for free?

5. Do you repair your tires for free?

6. Can I purchase road hazard insurance for your tires?

7. How long will it take to have services performed?

Taking care of your tires:

1. Make sure to have the alignment checked and/or corrected with new tires.

2. Keep tire air pressure set to manufactures specification (usually 26-32 psi)

3. Rotate, balance and inspect tires @ 6,000 miles.

4. Don't run a low or flat tire.

5. If the steering wheel is off-center or the car pulls have it checked ASAP.

6. If you hit a curb, huge pothole, or other object have it checked ASAP.