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Tire Terms

Aspect Ratio Section height/section width x 100 - ratio between tire height and width
Asymmetric When opposite sides of a tire's tread pattern are not identical.
Backside Setting The distance from the mounting surface of the wheel, which contacts the hub, to the back rim flange. It is sometimes referred to as the backspacing or backside measurement.
Balance The even distribution of weight on a mounted wheel and tire.
Bias-Belted Tire A passenger type tire which has two rubberized plies of cords which are crossed over one another at an angle (on a bias) plus two reinforced belts which encircle the tires under the tread.
Block Tread Design A tire tread pattern made of raised rubber compound segments.
Bolt Circle Sometimes referred to as bolt pattern: The number of lug holes on the diameter of the imaginary circle that each lug hole is centered on.
Carcass The portion of a tire that is the foundation for the tread, belts, bead and sidewall.
Casing The structure of tire cords locked around wire beads.
Compound  The general term referring to the chemical formula for the tread material.
Criss-Cross Torquing The recommended sequential tightening of the lug nuts in a pattern across from one another to help ensure even tightening.
Grooves Circumferential channels between and the tread ribs of a tire.
Hub Centric A situation where the center bore of the wheel is made to match up with the diameter of the automobile hubs; the wheel is then balanced by the center hold rather that the lug holes.
Hydroplaning Loss of traction at high speeds caused by a wedge of water that lifts a tire off the road surface.
Load Rating The maximum weight that the tire is designed to carry; dictated by the tire's construction. Metric passenger type tires are offered with a Standard Load Rating (up to 35 psi), or Extra Load Rating (up to 41 psi). LT Metric (truck type) tires are offered with ply ratings of C (8 ply), D (8 ply), and (10 ply) and at various inflation pressures up to 80 psi.
Low Profile  A term describing a tire with a low relative aspect ratio or series classification (short sidewall, wide tread).
Negative Offset A condition where the wheel's mounting surface is closer to the inside of the wheel; when the mounting surface is inboard the wheel's centerline.
Nominal Rim Diameter Diameter of rim seat supporting the tire bead. Examples: 13', 15" and 16.5".
Offset The positive or negative distance from the wheel's centerline to the mounting surface of the wheel.
Overall Diameter  The diameter of the inflated tire without any load.
Overall Width  Maximum width in cross-section of the unloaded tire including protruding sides ribs and decorations.
Ply  A layer of rubber-coated fabric or wire making up the tire casing.
Positive Offset  A condition where the wheel's mounting surface is closer to the street side of the wheel; when the mounting surface is outboard the wheel's centerline.
Radial Ply Tire A type of tire that has one or more rubberized plies of cords running from bead to bead (at right angles to the tread and parallel to each other), plus two or more plies of reinforced belts which encircle the tire under the tread.
Ribs  Part of a tire tread pattern created by grooves that run circumferentially around the tire.
Rim Diameter  The distance between bead seat to bead seat at beat seat radius.
Rim Flange  The edge of the wheel's rim that the clip-on weights attach to. 
Rim Width  The distance between the inside surfaces of the rim flanges.
Section Height The distance from rim seat to outer tread surface of an unloaded tire.
Section Width The linear distance between the outside sidewalls of an inflated tire without any load (exclusive of protruding side ribs and decorations).
Series A numerical representation of a tire's aspect ratio; for example, 50 series.
Shoulder Blocks  Raised rubber compound segments on the part of the tire tread nearest the sidewall.
Sipes Slits in the tire tread. Small cuts in the surface of the tread to improve traction.
Steel Belt A belt material used in radial tires. Its high stiffness provides good handling and low treadwear.
Tire Profile A term representing the portion of a tire measured as its aspect ratio or series.
Tread Blocks Raised rubber compound segments on the outside visible part of a tire.
Tread Width  The portion of the tread design that comes in contact with the road.
Unsprung Weight  The total weight of the automobile's components not supported by the suspension system; wheels and tires are prime examples.
UTQG Uniform Tire Quality Grade - A government-mandated tire rating system based on a tire's performance in treadwear durability, traction, and temperature resistance. UTQG ratings are branded on the tire's sidewall.
Varied-Pitch Ratio Variations of angles and sizes of a tire's tread elements that reduce ride noise levels.
Zero Offset A condition where the wheel's mounting surface coincides with the centerline of the wheel

 

Irregular Tire Wear - Causes & Solutions
IRREGULAR WEAR COMMON CAUSE SOLUTION


FEATHERING

  • Improper alignment (TOE)

  • Worn or damaged steering 
    and/or suspension parts

  • Hard cornering

  • Check/correct alignment

  • Check/replace steering and/or suspension parts

  • Based on tread depth rotate/replace tire


CUPPING

  • Worn or damaged steering and/or suspension parts

  • Improper balancing

  • Check/replace steering and/or suspension parts

  • Check/correct balance

  • Check/replace wheels

  • Based on tread depth rotate/replace tire


ONE EDGE

  • Improper alignment (CAMBER)

  • Worn or damaged steering and/or suspension parts

  • Check/correct alignment

  • Check/replace steering and/or suspension parts


CENTER OR BOTH EDGES

  • Center wear - over inflated

  • Both edges - under inflated
                          overloaded
                          slow leak

  • Adjust air pressure

  • Check fitment

  • Check/correct air leak


Uniform Tire Quality Grading

The Federal Government Uniform Tire Quality Grading Standards (49 CFR 575.104) apply to passenger car tires only (but excludes deep tread, winter-type snow tires, temporary use spare tires, and tires with nominal rim diameters of twelve inches or less). Tires subject to the Standards are required to be graded on the performance factors of treadwear, traction and temperature. The grades are molded on the tire sidewall, and in addition for replacement tires, a label affixed to the tread lists and explains these grades. Tire characteristics defined in the Standards are as follows:

TREADWARE
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 1/2) times as well on the government course as a tire graded 100. The relative performance of tires depends upon the actual conditions of their use, however and may depart significantly from the norm due to variations in driving habits, service practices, and differences in road characteristics and climate.

TRACTION
The traction grades, from highest to lowest, are AA, A, B and C. These grades represent the tire's ability to stop on wet pavement as measured under controlled conditions on specified government test surfaces of asphalt and concrete. A tire marked C may have poor traction performance. WARNING: The traction grade assigned to each tire is based on straight-ahead braking traction tests, and does not include acceleration, cornering, hydroplaning or peak trac- tion characteristics.

TEMPERATURE
The temperature grades are A (highest), B and C, representing the tire's resistance to the gener- ation of heat and it's ability to dissipate heat when tested under controlled conditions on a specified indoor laboratory test wheel. Sustained high temperature can cause the material of the tire to de- generate and reduce tire life, and excess temperature can lead to sudden tire failure. The grade C corrosponds to a level of performance which all passenger car tires must meet under the Federal Motor Vehicle Safety Standard # 109. Grades B and A represent higher levels of performance on the laboratory test wheel than the minimum required by law. WARNING: The temperature grade for each tire is established for a tire that is properly inflated and not overloaded. Excessive speed, under inflation or excessive loading, either separately or in combination, can cause heat buildup and possible tire failure.

FOR EXAMPLE:

ALL PASSENGER CAR TIRES MUST CONFORM TO FEDERAL SAFETY REQUIREMENTS IN ADDITION TO THESE GRADES.

RMA OBSERVATION: Other factors affecting relative tire performance from one vehicle to another are: horsepower, automatic vs. manual transmission, gear ratios, etc.