The size of each soapbox was strictly controlled: maximum 1950mm long, maximum 1100mm wide, maximum weight of 135kg, and a minimum driver's eye-line, when seated in the cockpit, of 770mm. These dimensions were scrutineered (amid much histrionics) during the Festival by means of The Absolute Device – a bottomless wooden box of appropriate proportions that was placed over each soapbox. If it didn't fit the space, it wasn't fit to race.

There are two types of soapbox:

'Roadster’ - an open-cockpit, wide-track soapbox designed to allow the driver a swift exit in the event of an accident. For a distance of one arm length (the driver's) forward of the seat back, the sides of the body tub should be no higher than the hip of the seated driver; likewise the side squabs of any bucket seat. The steering wheel should not unduly impede rapid egress of the driver's legs from the footwell. The driver's seat shall be of low-back kart-style design, and the rear bodywork should not extend upwards beyond the top of the driver's seat. No seatbelts should be worn.

‘Streamliner’ – a closed-cockpit, narrow-track soapbox designed to retain the driver within a protected cockpit in the event of an accident. Bodywork is all-enveloping, designed to open from inside and outside without the use of special tools. A substantial roll-over bar should be sited at least 40mm above the top of the seated driver's helmet in a suitable position to protect his head, neck and spine. A second substantial roll-over bar should be sited at least 25mm beyond the driver's gloved knuckles when placed at 12 o'clock on the steering wheel. A (minimum) four-point seatbelt must be fitted and worn. N.B. 'Streamliner' soapboxes are permitted to use a narrower minimum wheel track of 650mm.

Soapboxes raced two abreast on the hill, with their aggregate time from one run each on Saturday and Sunday determining their final position. Failure to complete the course earned the entrant the same time as the day's slowest finisher, plus an additional five-second penalty. No push-starting, 'wheel tweaking' nor unsporting interference with a fellow competitor was allowed. No stored energy nor weapons were permitted. Before being allowed to compete, each soapbox had to partake in two compulsory Test and Scrutineering Days at Goodwood. The soapbox and its driver had to demonstrate sufficient competence and integrity to compete. A scrutineering panel assessed each design, paying particular attention to stability (checked by the dastardly 'Wiggle Woggle' test), accident protection, braking and the suitability of all load-bearing components, especially wheels. Where the panel found concern, the machine was suspended from competing until the issue had been addressed to the panel's satisfaction. Crashing was strictly prohibited, unless absolutely necessary.

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