Tread Wear

The following information relates to the tyre grading system developed by the National Highway Traffic Safety Administration which grades tyres by tread wear, traction and temperature performance.

Tread Wear

Tread wear grade is a comparative rating based on the wear rate of the tyre when tested under controlled conditions (specified government test course). For example, a tyre graded 150 would wear one and a half times less on the government course than a tyre graded 100. Relative performance of the tyres depends upon actual conditions of use and may depart significantly from normal due to variations in driving habits, service practices and differences in road characteristics and climate.

Traction

Traction grades, A (highest), B and C represent a tyre’s ability to stop in wet conditions measured on specified government test surfaces of asphalt and concrete.

⚠ Warning ⚠
PDI Inspection.
Traction grade is based on braking (straight ahead) traction tests and does not include cornering (turning) traction.

Temperature

Temperature grades, A (highest), B and C, represent a tyre’s resistance to the generation of wear and its ability to dissipate heat when tested under controlled conditions (specified indoor laboratory test road wheel). Sustained high temperature can cause the material of a tyre to degenerate and reduce tyre life; excessive temperatures can lead to sudden tyre failure. Grade ‘C’ corresponds to a level of performance which all passenger vehicle tyres must meet under Federal Motor Vehicle Safety Standard No. 109. Grades ‘B’ and ‘A’ represent higher levels of performance than the minimum required by law.

⚠ Warning
Temperature grade is established for a tyre that is properly inflated and not overloaded. Excessive speed, under inflation or excessive loading, whether separately or in combination, can cause heat build-up and possible tyre failure.

Maintenance

Factory installed tyres and road wheels are designed to operate satisfactory when inflated to the recommended inflation pressures (Refer to ‘Inspection and Verification’, page 4-5-3). The recommended pressures apply to vehicle loads up to and including the full-rated load capacity.

Correct tyre pressures and driving technique have an important influence on tyre life. Heavy cornering, excessively rapid acceleration and unnecessary sharp braking increase tyre wear.

Replacement tyres should follow the recommended:

• Size
• Speed rating
• Load range
• Radial construction type

The use of any other size or type may seriously affect:

• Safety
• Ride
• Handling
• Speedometer and Odometer calibration
• Vehicle ground clearance
• Tyre clearance between body and chassis
• Wheel bearing life
• Brake cooling

Wheels need to be renewed when:

• Impact damaged
• Heavily corroded
• Porous
• Wheel stud holes or seats become damaged
• They have excessive radial or lateral runout.

Safety

⚠ Warning
Do not mix different types of tyres on the same vehicle. Handling may be seriously affected resulting in loss of control.

⚠ Warning ⚠
Ensure that tyres are mounted with the sidewall marking ‘Outside’ showing on the outer sidewall face. Correct tyre rotational direction is critical.

⚠ Warning ⚠
A tyre and wheel must always be correctly matched. Wider or narrower tyres than recommended could cause danger through sudden deflation.

⚠ Warning
When changing a wheel, make sure that the vehicle cannot move. Always apply the parking brake and select the transmission park position (Automatic transmission only).

⚠ Warning
Never run the engine with one wheel off the ground, for example, when changing the wheel. The wheel resting on the ground may cause the vehicle to move.

⚠ Warning ⚠
Always tighten the wheel nuts to specification. Too tight may cause damage, too loose may allow the wheel to become detached.