Regions of a Tire
Tread Region - The "flat" area of the tread. The construction of the tread will determine the adhesion characteristics of the tire in all driving conditions.

Sidewall Region - The vertical portion of the tire that extends from the road surface to the rim. The manner in which the sidewall is constructed affects the ride and handling or the tire. A stiff sidewall provides quick steering response but a supple sidewall will flex to a greater degree and provide a smoother ride.

Shoulder Region - The curved region where the vertical sidewall of the tire meets the horizontal tread.

Bead Region - The narrow band between the sidewall and rim that comes into contact with the rim. The bead is responsible for anchoring the tire to the rim and maintaining a leak free seal while transmitting all forces (acceleration, turning, braking) between the vehicle and the road.
Tire Wear Warning Signs:
I - Sawtooth appearance on the edges
II - Faster wear on the outer edges
III - Faster wear on the front or rear drive tires
IV - Excessive wear on one side
V - Cups or dips in the tread

Tire-Tread Condition Diagnostic
Uneven or accelerated tire wear can be caused by wheel misalignment, worn suspension and steering components, and / or improper tire inflation.

The most critical alignment angle with respect to tire wear is toe. Camber is also important and can be affected by caster. Misalignment is usually caused by worn, loose, or bent suspension and steering parts (bad tie rod ends, idler arms, control arm bushings, ball joints, struts, etc.), but can also be due to spring sag or improper ride height.


Condition - Cause
Rapid Wear at Shoulders - Under inflation
Rapid Wear at Center - Over inflation
Cracked Threads - Under inflation or excessive speed
Wear on One Side - Excessive camber
Feathered Edge - Incorrect toe
Bald Spots - Wheel unbalanced
Causes of Tire Wear Problems
Your tires are not properly inflated or balanced
Your vehicle is misaligned
The shocks on your vehicle are weak
Your vehicle has loose front-end parts

Reading a Tire Sidewall - Example: P215/65R15 89H
"P" means this is a passenger car tire (as opposed to a tire made for a truck or other vehicle).

"215" Section Width: The width of the tire in millimeters from sidewall to sidewall. This measurement varies depending on the width of the rim to which the tire is fitted: larger on a wider rim, smaller on a narrow rim. The number on the side of tire indicates the width measured with the tire fitted to the recommended rim width.

"65" Aspect Ratio: The ratio of height to width; this tire's height is 65% of its width.

"R" Construction: How the plies are constructed in the tire carcass. "R" means radial. "B" in place of the "R" means the tire is belted bias construction. "D" in place of the "R" means diagonal bias construction.

"15" Rim Diameter: The diameter of the wheel in inches.

"89" Load Index: This tire has an industry-standard maximum load of 1,279 lbs. Different numbers correspond to different maximum loads. The maximum load is shown in lbs. (pounds) and in kg (kilograms), and maximum pressure in PSI (pounds per square inch) and in kPa (kilopascals). Kilograms and kilopascals are metric units of measurement.

"H" Speed Rating: This tire has an industry-standard maximum service speed of 130 mph. Tires using an older European system carry the speed rating in the size description: 215/65HR15. different letters correspond to different maximum service speeds.