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Tire Buying 101

How To Read a Tire's Sidewall

A lot can be learned by reading the tire's sidewall. The following illustrations show typical information on the sidewall of passenger car ang light truck tires.Being able to read and understand the information molded on a tire's sidewall will make it easier for you to know what tire you need.

Tire Sizing Systems

There are a number of different systems in use today that describe the various tire sizes used on performance, passenger and light truck vehicles. An attempt is currently underway to develop a worldwide system, but presently you must be familiar with several different systems.

PASSENGER CAR TIRE SIZING SYSTEM

NUMERIC SIZING SYSTEM.

The first system developed for tire sizing was used until the late 1960s, but provided only the cross section width of the tire and the rim diameter in inches. If the section width ended in zero (e.g., 7.00-14 or 7.50-14), the tire has a common aspect ratio of about 92. For section widths not ending in zero (e.g., 8.25-15), the tire was considered "low profile" with an aspect ratio of about 82.

ALPHA-NUMERIC SIZING SYSTEM.

  • A - Load Rating
  • B - Radial Construction
  • C - Aspect Ratio
  • D - Rim Diameter

In 1968, a new concept was introduced worldwide. The Alpha-Numeric Sizing System is a load-based system where tires are designed by their load-carrying capacity and aspect ratio. The first letter is the load and size relationship, with letter, the smaller the size and, of course, the lower the load-carrying capacity of the tire.

METRIC SIZING SYSTEM.

  • A - SECTION WIDTH (mm)
  • B - ASPECT RATIO
  • C - RADIAL CONSTRUCTION
  • D - RIM DIAMETER

Because Europe primarily uses the metric system of measurement, the Metric Sizing System was developed. It is essentially a conversion of the Numeric Sizing System. Section widths are notated in millimeters instead of inches. Originally, tires not identified with an aspect ratio were assumed to be 82-series. When 60- and 70-series tires appeared, the aspect ratio was added to the nomenclature, similar to the P-Metric System.

ISO METRIC SIZING SYSTEM.

  • A - Section Width (mm)
  • B - Aspect Ratio
  • C - Radial Construction
  • D - Rim Diameter
  • E - Load Index
  • F - Speed Rating

The International Standard Organization (ISO) Metric System combines the Metric System with a service description provides the load index along with the speed-rating symbol.

MILLIMETRIC SIZING SYSTEM

  • A - Section Width
  • B - Aspect Ratio
  • C - Radial Construction
  • D - Rim Diameter (mm)

The Millimetric Sizing System is similar to the Metric Sizing System except that the rim diameter is also represented in millimeters. These rim diameters are unique in size and can only be used in combination with each other.

LIGHT TRUCK TIRE SIZING SYSTEMS

LIGHT TRUCK NUMERIC SYSTEM

  • A - Section Width
  • B - Radial Construction
  • C - Rim Diameter
  • D - Light Truck Designation

Similar to the Numeric Sizing System for cars, it lists the section width in inches, construction type, rim diameter in inches, plus the light truck designation

LIGHT TRUCK METRIC SYSTEM

  • A - Light Truck Metric System
  • B - Section Width (mm)
  • C - Aspect Ratio
  • D - Radial Construction
  • E - Rim Diameter

Similar to the P-Metric System, except the P is replaced with the LT (Light Truck) designation. Also, LT-Metric and P-Metric tires differ in construction.

LIGHT TRUCK HIGH FLOTATION SYSTEM

  • A - Tire Diameter (in.)
  • B - Section Width
  • C - Radial Construction
  • D - Rim Diameter
  • E - Light Truck Designation

The same as the Light Truck Numeric System with tire diameter added to the front.

Speed Ratings & Load-Carrying Capacity

Load Index

Many tires come with a service description added on to the end of the tire's size. These service descriptions contain a two-digit number (load index) and a letter (speed rating). The load index is a representation of the maximum load each tire is designed to support. Because the maximum tire load-carrying capacity is branded on the tire's sidewall, the load index is used as a quick reference.

Speed Rating

In Germany some highways do not have speed limits and high speed driving is permitted. Speed ratings were established to match the speed capability of tires with the top speed capability of the vehicles to which they are applied. Speed ratings are established in kilometers per hour and subsequently converted to miles per hour (which explains why speed ratings appear established at "unusual" mile per hour increments). Despite the tire manufacturer's ability to manufacturer tires capable of high speeds, none of them recommend the use of their products in excess of legal speed limits. The maximum operating speed of a vehicle must be limited to the lowest speed rated tire on the vehicle.

How To Mount & Balance Tires

Balanced tires provide a smooth ride and help protect your tire from uneven tread wear. As new vehicles become lighter it's becoming increasingly important to keep your tires balanced. Heavier cars helped smooth out the ride and mask vibrations. You should let an expert mount and balance your tires, but you can do the job yourself if you have the expertise.

Moderately Challenging

Instructions
Things You'll Need

  • Tire stem removal tool
  • Bead breaker or rubber mallet
  • Dishwashing soap or Murphy's Oil
  • Large screwdriver
  • Wheel balanacer
  • Tape
  • Wheel weights
  1. Let the air out of the tire using a tire stem removal tool.
  2. Break the bead on the old tire with a bead breaker. If you don't have a bead breaker you can use a rubber mallet. Do not hit the rim with the mallet.
  3. Once the beads are loose, lubricate the old tire with dishwashing soap or Murphy's Oil. Use a large flathead screwdriver to pry the beads up over the rim. Let the opposite side of the tire slip under the lip on the rim as you pry the other side over the rim.
  4. Lubricate the new tire and put it on the same way you took the old one off. If you're using tubeless tires, replace the valve stem before putting on the new tire (take the old one out, then pull the new one through from the inside). Using tubeless tires will make it a bit harder to inflate. The proper way is to use a valve stem core tool, unscrew the core and inflate the tire. There should be enough volume flowing through the stem to blow the tires out and seal up the beads. Using a tube is easier. Insert the tube inside and inflate it. Then deflate it and inflate it again.
  5. Place the wheel on the balancer, making sure the wheel is centered. Spin the wheel and allow it to come to a natural stop.
  6. With chalk mark the highest point on the wheel. Cut off a piece of weight and tape it to this part of the wheel. Turn the wheel so the mark is at the 3 o'clock position, then release the tire. If the chalk line points to 6 o'clock weight needs to be removed. If the mark points to 12 o'clock, weight needs to be added. Repeat this step until the tire is balanced.
  7. Attach the wheel weights with the adhesive side first.
  8. Mount the wheel back onto the car.

Basic Tire Repair

Here at Onlinetires.com we would like to help you, the consumer in any way possible to get the most out of your tires and this is a step by step process on how to repair your flat tire if this problem ever arises.

This article on Basic Tire Puncture Repair is the first in a four-part series on basic services performed in tire stores. This first installment breaks down each repair step with photographs and descriptive captions and should be helpful to not only newly trained technicians, but also veterans who want to brush up on their techniques. The information is a compilation of accepted industry procedures and standards from the Rubber Manufacturers Association and the Tire Industry Association; the photos were supplied by Myers Tire Supply/Patch Rubber Co., a supplier of repair materials and tools.

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