Lowering vehicle height
Acceptable 'eyebrow heights' (the measurement from the centre of the wheel vertically upward to the edge of the mudguard) or 'bump rubber clearance heights' (the clearance between the bump rubber and corresponding contact point) for most passenger vehicles can be found on the Passenger Car Track List for 1970 and later vehicles .
Other requirements for lowering a vehicle include:
• Either front or rear, the suspension travel must not be reduced by more than one third of that specified by the vehicle manufacturer
• The vehicle must also retain 100mm ground clearance which is measured between any part of the vehicle and the ground
• All measurements must be carried out with the vehicle on level ground in its normal operating but unladen state
• Coil springs must not be shortened by cutting, and no suspension component is to be subjected to heating
• Lowering blocks may be used on leaf spring suspensions provided they are manufactured from steel, aluminium, or metal and to be positively located to the axle spigot hole and the spring centre bolt. Note: the axle mounting 'U' bolts are not permitted to be below the lower rim height
Wheels and tyres
From 1973 all cars are to be fitted with a tyre placard (usually fitted in the glove box, the engine bay or on a door pillar).
This specifies the wheel and tyre combinations recommended by the vehicle manufacturer. This placard also specifies load capacity, speed rating and the recommended tyre air pressure.
Replacement wheels and tyres may be fitted provided that they comply with the following requirements:
• Ensure that the replacement wheels have been designed for the vehicle's hub and have the same bolt or stud spacing as the original and the same centre location method.
• Ensure the offset of the rim is not reduced by more than 13 mm from the original rim.
• The wheel track must not be increased by more than 26 mm beyond the maximum specified by the vehicle manufacturer. Maximum allowable track measurements for individual vehicle models can be obtained from the Department of Planning, Transport and Infrastructure.
• Spacers are not permitted between the hub and wheel unless originally fitted by the vehicle manufacturer.
• Rims that have been widened by inserting a spacer band are not permitted.
• Rims must have no more than one circumferential weld.
• Welding must be carried out in accordance with recognised engineering standards, and the rims must comply in all respects with specifications contained in the Tyre and Rim Association of Australia - Standards Manual.
• The wheels and tyres must not foul the body, suspension or any part of the vehicle under any operating conditions and must not project beyond the bodywork when the wheels are in the straight ahead position and viewed from above.
• If the wheels of a vehicle are retained by multiple nuts or set screws, not by splines and a single nut, then the wheel nuts must match the tapered holes in the wheel and the nuts must be engaged for their full depth of thread.
• Wheel rims fitted to passenger cars manufactured after 1 July 1985, which are not original equipment or an original equipment replacement by the vehicle manufacturer, must be indelibly marked with the wheel's nominal diameter, width and offset and with identification of the manufacturer of the wheel and the standard to which the wheel was manufactured.
• The use of composite wheels (two or three piece) is permitted if they are manufactured and marked in accordance with the standards described above and fitted to vehicles manufactured on or after 1 July 1985.
• Modifications to disc brake calipers, hubs and suspension and steering components to enable the fitting of replacement wheels is not allowed without a certificate from a MR426 Chartered Professional Engineers Open in new window.
