Basic Tyre Terms
Learn How to Speak Tyre Like a Dealer
ALIGNMENT
When all wheels on the vehicle are adjusted so that they are pointed in the optimum direction relative to the road and each other.
BALANCE/IMBALANCE
The state in which a tyre and wheel spin with all their weight distributed equally. To correct an imbalance, a trained mechanic will add weights on the interior or exterior of the wheel.
BEAD
The section of the tyre that sits on the wheel. Inside, there is a round hoop of steel wires, wrapped or reinforced by body ply cords, that clamps the tyre firmly against the wheel rim.
CONTACT PATCH
The area in which the tyre is in contact with the road surface. Also called footprint.
DEFLECTION
The tread and sidewall flexing where the tread comes into contact with the road.
GROOVE
The space between two adjacent tread ribs; also called tread grooves.
MOUNTING
This is the act of putting a tyre on a wheel and ensuring that the assembly is balanced. When you purchase new tyres, they need to be professionally mounted. It is also standard for the tyre dealer to charge a nominal fee for a valve stem.
OVERSTEER
The tendency for a vehicle, when negotiating a corner, to turn more sharply than the driver intends. The rear end of the vehicle wants to swing toward the outside of a turn. A handling condition in which the slip angles of the rear tyres are greater than the slip angles of the front tyres. An oversteering car is sometimes said to be "loose," because its tail tends to swing wide.
PULL
A condition in which a vehicle swerves to one side without being steered in that direction, as a result of irregular tyre wear, improper front and/or rear wheel alignment, or worn or improperly adjusted brakes.
RIM
That portion of a wheel to which a tyre is mounted.
RIM DIAMETER
The diameter of the rim bead seats supporting the tyre.
ROLLING RESISTANCE
The force required to keep a tyre moving at a uniform speed. The lower the rolling resistance, the less energy needed to keep a tyre moving.
ROTATION
The changing of tyres from front to rear or from side to side on a vehicle according to a set pattern; provides even treadwear. Rotating your tyres on a regular basis (every 6,000-8,000 miles) is a simple way to add miles to their life. See your tyre warranty for more information on recommended rotation.
RUN FLAT TECHNOLOGY
Tyres that are designed to resist the effects of deflation when punctured, and to enable the vehicle to continue to be driven at reduced speeds and for limited distances.
SHOULDER
The area of a tyre where the tread and sidewall meet.
SIPES
Special slits within a tread block that open as the tyre rolls into the contact patch then close, breaking the water tension on the road surface and putting rubber in contact with the road to maintain adhesion, increasing wet and snow traction.
SUSPENSION
The various springs, shock absorbers and linkages used to suspend a vehicle's frame, body, engine, and drivetrain above its wheels.
SYMMETRICAL TREAD DESIGN
Uniform tread pattern on both sides of the tread for better performance in specific conditions and on specific roads.
TYRE PLACARD
A metal or paper tag permanently affixed to a vehicle, which indicates the appropriate tyre size and inflation pressures for the vehicle. The placard can ordinarily be found on either the driver's doorpost, the glove box lid, or the fuel-filler door.
TRACTION
The friction between the tyres and the road surface; the amount of grip provided.
TREAD
That portion of a tyre that comes into contact with the road. It is distinguished by the design of its ribs and grooves. Provides traction in a variety of conditions, withstands high forces, and resists wear, abrasion, and heat.
TREAD DEPTH
The depth of usable tread rubber measured in 32nds of an inch. If a tyre comes new with 10/32nds of rubber, you have 8/32nds of usable rubber. Tyres must be replaced when the wear bars are visible at 2/32nds.
TREAD LIFE
The life of a tyre before it is pulled from service; mileage.
UNDERSTEER
The handling characteristic in which the front tyres break loose because they are running a larger slip angle than the rear tyres. Also known as plowing.
VALVE
A device that lets air in or out of a tyre. It is fitted with a valve cap to keep out dirt and moisture, plus a valve core to prevent air from escaping.