A cautionary ‘heads-up’ regarding the need for entrants of historic vehicles (except Groups Na, Nb, Nc, C, A, Sa, Sb and Sc – which have their individual group regulations) to ensure that their cars comply with the roll-over protection requirements of Motorsport Australia.
Effective roll bars must be fitted to all competing vehicles. Those requirements are specified in the 2020 Motorsport Australia Manual as follows –
SPECIFICATIONS OF AUTOMOBILES 5th Category – Historic Cars Vehicle Eligibility – General Requirements
(i) General configuration: With the driver in the normal seated position, the roll bar shall:
(A) be of height at least level with the top of the driver’s helmet;
(B) not overhang the driver’s helmet, but be within six inches (150mm) of the driver’s helmet;
(C) in combination with the vehicle structure shall not leave unprotected any part of the driver’s shoulder profile (when viewed from front or rear);
(D) be adequately braced longitudinally.
You can look this up yourself at – https://www.motorsport.org.au/docs/default-source/manual/historic/hi03-gen-requirements.
Often modifications creep in to our cars over time, such as seat cushion replacement/adjustment or other minor alterations, and the result can be that the driver’s helmet then exceeds the height of the roll bar.
That measurement will be checked from time to time by the event scrutineers and a problem will occur if your helmet is too high. Being a significant safety Issue, an exception will not be given.
And in any case, bouncing along on your helmet in lieu of the roll bar is NOT an option.