The Queensland TAC wants to ensure that our Federation members are aware of the track rules that apply to building hot rods in our “California of Australia” state, Queensland.
In the 1970’s, with the advent of the first mag wheels, the government in conjunction with the wheel makers, made a decision to permit an over-track allowance of one inch (25mm) to give the wheel makers some room to move with offsets. Most of the inch was probably taken up with the additional thickness of the mag wheel hub compared to the steel wheel. Anyway, the arbitrary decision to allow an inch has stayed with us to this day, even though it has no basis in engineering. The only variation from this rule is for hot rods in Queensland where the rule has been varied to 2” or 50mm allowance for live axle rear suspensions and unlimited for floating hubs.
Despite the arbitrary one inch rule, the intent of limiting track variation is to minimise the risk of axle and bearing failure. As track increases, the bending moment on the axle increases as the wheel load is moved further away from the bearing.
The QSRTAC has to check track as a checklist item in our LH9 and LH10 Codes of Practice. Wheels and track confuse people but only because they don’t do any homework.
Track is measured as the centre distance between the two wheels on a suspension, so if you bolt the factory wheels to the unit and take a measurement and then bolt your chosen wheels on, then if the increase in the result varies by more than the allowance you’re in trouble.
For example, looking at the most popular differential used in modified vehicles, the 9” Ford, we know that the flange to flange measurement is a safe guide to the legal track and then, for Queensland, we can add another inch to give the legal hot rod track.
Track issues are not all that simple so we encourage our members to contact the local QSRTAC representative to discuss front end and differential selection, wheel choices, floating hubs and any related issues. Suspension and wheel selection is a costly part of building a hot rod so get help when its needed.