Alignment
If you feel that your vehicle pulls either to the left or to the right, when travelling a straight road, it could mean that your wheel alignment is out. Essentially, your wheels need to be parallel to each other and perpendicular to the ground.
Your local tyre dealer will be able to adjust your alignment using special tools. Proper alignment will ensure maximum tyre life and better fuel economy.
Wheel Alignment is often confused with Balancing but the two are completely different. An unbalanced wheel will cause vibration at certain speeds where an alignment issue will not.
Aquaplaning
When driving on wet roads, it is possible for the car to ride on a thin layer of water. It’s the job of the tyres to cut through standing water and good tyres with good tread depth will do so. If you drive through water and feel the steering go ‘loose’, this is the effect of aquaplaning. In serious cases, you can lose control of the vehicle and great care should be exercised when driving in wet conditions.
Aspect Ratio
Ratio of height to section width. On a 255/55/18 tyre - Height / Section = 55%
Asymmetric
Different tread patterns featured on either side of the tread that enhance and optimize performance for both wet and dry handling. The inside shoulder has more grooves for water evacuation and massive tread blocks on the outside shoulder make for maximum handling.
Balancing
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.
Bar
Unit for measuring air pressure (1 bar = 14.50 psi).
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.
Carcass
The supporting structure of the tyre consisting of plies anchored to the bead on one side and running in a radius to the other side and anchoring to the bead. Also called casing.
Cold Weather Tyres / Winter Tyres
When temperatures fall below 7°C the rubber on standard tyres becomes harder which leads to a reduction in their handling capabilities. Cold Weather Tyres contain more natural rubber and additional sipes, which counteract the hardening effects on the rubber allowing the tyres to grip the road surfice.
Contact Patch
The area in which the tyre is in contact with the road surface. Also called footprint.
Tyres that are rated to carry a higher load by virtue of having a maximum inflation pressure higher than the standard maximum.
Load Index
This can be found on the tyre wall and is a guide indicating the maximum weight a tyre can carry at speeds specified in the speed rating of the tyre.
Maximum Inflation Pressure
The maximum air pressure to which a cold tyre may be inflated; can be found moulded onto the sidewall or in the vehicle hand book.
Original Equipment
Tyres selected by a vehicle manufacturer that best match tyre performance to vehicle performance characteristics. Also known as OE.
Over Steer
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.
Ply
A rubber-coated layer of fabric containing cords that run parallel to each other and make up the structure of a tyre. Layers of this material are called plies, and they extend from bead to bead, between the inner liner, and belts or tread. Plies are usually reinforced with either textile or steel cords.
PSI
This is the air pressure in the tyre measurement in pounds per square inch.
Rim
There are 2 rims on each wheel and this is where the bead seats when the tyre is inflated
Rim Size
Normally measured in inches, the rim size is the outside diameter of the wheel, for example 205/55/16 – 16 is the rim diameter in inches
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.
Run-Flat
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.
Sidewall
The portion of a tyre between the tread and the bead. Protects the tyre against impacts with curbs, etc. This is also where the sidewall markings can be found which tell you important information regarding the tyre.
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.
Speed Rating
An alphabetical code (A-Z) assigned to a tyre indicating the range of speeds at which the tyre can carry a load under specified service conditions.
Tread
The 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 millimetres. The minimum legal tread depth is 1.6mm and all Michelin tyres come with tread depth indicators (small rubber blocks in between the tread groves) set at 1.6mm
Tyre Pressure
The pressure of the air inside the tyre can be measured in PSI or Bar. It is important to maintain the vehicle manufacturer’s recommended pressures as it impacts fuel economy, the life of the tyres and the handling of the vehicle.
Tyre Pressure Monitoring System (TPMS)
All newly manufactured vehicles now come fitted with a TPMS system. The system monitors the pressure inside each tyre and provides a warning should it detect any pressures outside of the parameters set by the manufacturer – either too high or too low.
Under Inflation
Operating a tyre without sufficient air pressure is not only dangerous it also increases fuel consumption and can cause irreparable damage to the tyre. All tyre pressures should be checked regularly.
Under Steer
The handling characteristic in which the front tyres break loose because they are running a larger slip angle than the rear tyres. Driving into a corner at too great a speed that the vehicle’s mass carries it beyond the tyre’s ability to grip the road surface will create under steer.
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. The valve should be replaced at the same time as the tyres. |
