Aspect ratio
The relationship between a tire’s height (sidewall) and its width, expressed as a percentage. It’s the second number in a tire size designation (e.g., in P205/65R15, the aspect ratio is 65).
Asymmetrical tire
A tire with a different tread pattern on its inner and outer sides, designed to provide specialized performance characteristics (like better cornering and wet traction). π
Bead
The part of the tire that seats against the wheel rim. It contains strong steel wires wrapped in rubber to hold the tire firmly on the whee
Cupping
A form of tire wear characterized by scooped-out, localized, irregular dips around the tire’s circumference, often caused by worn shocks, struts, or improper balance
Direct or active TPM
A Tire Pressure Monitoring System that uses individual pressure sensors mounted inside each wheel to measure and transmit real-time pressure data directly to the vehicle’s computer. π‘
Directional tire
A tire designed to rotate in only one direction for optimum performance (often for water evacuation and high-speed stability). It has an arrow on the sidewall indicating the correct rotation
Drop center
The lowest part of the wheel rim’s circumference, designed to allow the tire bead to be mounted and dismounted more easily.
Dynamic balance
: A type of wheel balancing that considers both vertical and lateral (side-to-side) weight distribution while the wheel is spinning, correcting weight imbalances across the entire width of the wheel
Hub
The central part of the wheel that mounts directly onto the vehicle’s axle, usually covering the wheel bearin
Indirect or passive TPM
Tire Pressure Monitoring System that uses the ABS (Anti-lock Braking System) wheel speed sensors to monitor tire pressure. If a tire loses pressure, its rolling radius changes, causing it to spin at a different rate, which the system detects.
Lateral runout
The measurement of how much a tire or wheel wobbles from side-to-side (parallel to the axle) as it rotates.
Load rating
A number on the tire sidewall that indicates the maximum weight (in pounds or kilograms) that the tire can safely carry when properly inflated.
Overinflation wear
Tire wear pattern where the center of the tread wears out faster than the edges because the excessive pressure causes the center of the tread to bulge out and bear most of the load. π©
Plies/belts (tire)
Layers of fabric (like polyester or nylon) and steel cord that form the structure and strength of the tire carcass and tread. Plies form the body, and belts reinforce the tread area.
- Radial runout
The measurement of how out-of-round a tire or wheel is (perpendicular to the axle), measured as the variation in radius from the cent
Speed rating
A letter on the tire sidewall that indicates the maximum safe speed at which the tire is designed to perform for an extended period under a standard load.
Static balance
A simple wheel balancing type that only considers the up-and-down (vertical) weight distribution of a wheel assembly. It corrects weight imbalances in one plane.
Temperature rating
A letter (A, B, or C) indicating the tire’s resistance to heat generation and its ability to dissipate heat. ‘A’ is the best.
Tire rotation
The practice of moving the tires from one wheel position to another on a vehicle to ensure even wear and maximize tire life.
TPMS
An electronic system designed to monitor the air pressure inside the pneumatic tires on various types of vehicles and alert the driver when pressure is significantly low.
Traction rating
A letter (AA, A, B, or C) indicating a tire’s ability to stop on wet pavement as measured in a straight-ahead skid test. ‘AA’ is the best.
Treadware rating
A comparative number (e.g., 400) indicating the tire’s projected life or durability compared to a control tire rated at 100 under test conditions. Higher numbers mean longer life.
Treadwear bar
Small raised bars of rubber molded into the tread grooves at 2/32 of an inch (1.6 \text{ mm}) depth. When the tread is worn down to the level of these bars, the tire needs replacement.
Underinflation wear
Tire wear pattern where the edges (shoulders) of the tread wear out faster than the center because the low pressure causes the edges to bear most of the load. π
