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How to Buy Tires and How to Decode a Tire Code

Dan Ferrell writes about do-it-yourself car maintenance and repair. He has certifications in automation and control technology.

If you don't know how to buy tires for your vehicle don't worry, you're hardly alone. Most drivers just go with the tires suggested by their car manufacturer, or by a relative or friend. Yet, the recommended tire may not necessarily produce the best results for your own vehicle.

Many variables affect tire durability, like driving patterns, road conditions, vehicle mechanical condition (mainly suspension and alignment), and climate.

Whether you just want to replace a set of worn-out tires or find the best ones for the new geographic area you just moved into, this guide will help you make an informed decision depending on your particular car, driving pattern, and the road ahead of you.

Tire Codes Give You a Wealth of Information

Much of the information you need when choosing a new set of tires you'll find it right on a tire sidewall. If you look closely at the sidewall of your current set of tires, you'll see labels with numbers and letters denoting the different tire characteristics or ratings of that particular tire. This may seem like cryptic messages to you right now. After you finish this article, though, you'll know how to decipher this information, and use it to help you choose a new set of tires.

So let's check those codes you'll need to know.

First, check which tires your car manufacturer recommends. You'll want to compare this information to the codes described here. To find the standard tires for your vehicle, look in your car owner's manual, the tag on the driver side pillar, or on one of the door posts on your car.

Tire Size Markings

Tire size markings consist of an alphanumeric code that looks like this: P185/65 R14.

  • The first letter of the code designates the tire for a passenger (P) vehicle. Other designations include (T) temporary and (C) commercial.
  • The "185" number, represents the tire's width in millimeters (from wall to wall - or from side to side). Two digits follow this number. The number 65, in this example, tells you the height of the tire--from bead to tread--as a percentage of tire width (65 percent of 185mm). The lower the number, the wider and shorter the tire.
  • The letter "R" in the code means the tire has a radial design construction. Other may specify a "B" (belted bias) or "D" (bias play) design. Finally, the number 14 represents the rim diameter in inches.

Service Description Code

After the tire size label, you'll find the service description code: a two-digit number followed by a single letter. For example, 73S.

  • The first couple of digits represent the load index value, load carrying capabilities, or maximum weight this particular tire may carry at the recommended inflation pressure. A tire with a load index of 73, for example, has the capacity to carry 805 lbs (365 Kg), and a tire with an index of 92 can carry 1389 lbs. (630 Kg). A load index may go from 65 to 150. On some tires, you'll see this index spelled out, for example MAX. LOAD 1389 Lbs.
  • The single letter besides the load index refers to the speed rating. Common tire speed ranges go from B (around 30mph/50Kmh) up to Z (around 150mph/241kmh). Tires come in varied speed ratings, depending on its intended use. For example, you may use a rate L (75mph/120kmh) tire on a vehicle suitable for off-roads, and a rate S (112mph/180kmh) on a family sedan. NOTE: Check the load index and speed rating tables reference below.

Temperature Grades

* "A", "B", or "C" designate tire temperature grades. For example, a TEMPERATURE A graded tire will dissipate heat and stand heat buildup better than a tire with grade "B" or "C", and will have a longer service life. A better choice if you live in Arizona or a similar state with high summer temperatures.

Tire Traction Grades

Tire traction grades also use letters: "AA", "A", "B", and "C", with "AA" reserved for the best traction. It may read "TRACTION AA". A tire with an "AA" traction index gives you a much better grip when stopping on wet pavement or asphalt.

Tread Wear Grades

Tire tread wear grades go from 100 up to 500. The higher the number the better the tire's ability to withstand wear. You may see "TREAD WEAR 400". However, be careful when comparing tires tread wear. You can only compare wear rating to tires of the same line and brand. A sport tire with grade of 400 from brand X, for example, doesn't have the same endurance as one from a touring line with the same 400 grade from brand Y. Even more, this grade doesn't take into account varied climates, vehicle alignment, driving patterns or road conditions.

Common Tire Load Indexes

Source: Wikipedia
https://en.wikipedia.org/wiki/Tire_code#cite_note-etrto.org-12

CodeWeight

85

515 kg (1,135 lb)

86

530 kg (1,170 lb)

87

545 kg (1,202 lb)

88

560 kg (1,230 lb)

89

580 kg (1,280 lb)

90

600 kg (1,300 lb)

91

615 kg (1,356 lb)

92

30 kg (1,390 lb)

93

650 kg (1,430 lb)

94

670 kg (1,480 lb)

95

690 kg (1,520 lb)

Common Tire Speed Reatings

source: https://en.wikipedia.org/wiki/Tire_code#cite_note-etrto.org-12

Codempgkmh

L

75

120

M

81

130

N

87

140

P

94

150

Q

100

160

R

106

170

S

112

180

T

118

190

U

124

200

H

130

210

V

149

240

So What Type of Tires Do You Need?

OK. You got the information you'll need to find your next set of tires. But before you start planning, read this section. It is designed to help you from the driver's perspective when considering all those ratings and indexes you'll find.

Let's explore your needs as a driver.

  • What is your driving patterns? Do you drive mostly within the city, on the highway, or both? If you drive mostly in light traffic, perhaps you need a good set of all-purpose tires. These tires typically have a tall profile and good traction, and come rated for S or T (112-118mph) speeds.
  • Do you drive on dirt roads often? Do you use winding roads in the mountains on your daily commute? Perhaps a higher speed rating than the one recommended by your car manufacturer will suit your car better. You'll get better handling, steering and cornering. They have a lower profile—shorter height—than ordinary passenger tires, but with a wider tread area for better traction.
  • What is your region's climate like? Do you drive on wet or snow-covered roads for a few months of the year? Possibly a set of M+S (mud and snow) tires with traction "A" will be better. Winter tires will help you handle snow, ice, slush and rain much better than all-season tires.
  • Do you own a light pickup truck or SUV? Sport tires have better stability and handling at high speeds than common passenger vehicle tires. And you can choose from performance, high-performance and ultra high-performance tires. if you often carry equipment and materials, you may want to consider a higher load capacity than the one recommended by your car manufacturer. Within this range you may select from on/off-highway, all-purpose, and all-terrain.

At this point, you can better sort through the options you'll find. Start by making a profile of one or more tires suitable for your car or truck, taking into account your car manufacturer recommendations, your driving patterns, and your geographic area characteristics. And, of course, your budget.

Once you have a close idea about the characteristics you want on your tires, visit SaferCar.gov where you can check a list of tires by brand, along with ratings for some product lines they offer. Also, visit tire manufacturers online to further narrow your list or find the best deals.

When you know how to buy tires and select your tires with care, you'll not only have a long lasting tire for your vehicle, but a quality and safer ride too.

Test Your Knowledge of Radial Tires

For each question, choose the best answer. The answer key is below.

  1. What are Two Common Materials Used on Radial Tires?
    • Copper and nickel
    • Fiberglass and steel
    • Aluminum and ceramic
    • Bronze and stellite

Answer Key

  1. Fiberglass and steel

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.