To provide a universal basis for these tax calculations, the Royal Automobile Club (RAC) developed the ‘tax horsepower rating’. This was derived not from actual engine output, but by an esoteric mathematical formula based on three engine measurements, all the more arcane when expressed in the prevailing imperial units: an assumed mechanical efficiency of 75%; a mean cylinder pressure of 90lbs per square inch; and a mean piston speed of 1,000 feet per minute. Since these differed from engine to engine, in reality, the resulting figure was almost entirely arbitrary, but could be applied by manufacturers and bureaucrats alike. Using this formula, the new Rolls-Royce was tax-rated by the RAC at 40 horsepower; in fact, it developed 50. Hence it was given the prosaic ‘40/50 H.P.’ designation on launch, so clients would know both the level of duty they would have to pay and how much power they could expect.
As an engineer, Royce was probably quite comfortable with this functional naming convention, but not so Claude Johnson. To his showman’s mind, it lacked distinction, resonance, romance and glamour; and it certainly failed to properly suggest the desirable, best-in-class motor car envisioned by Charles Rolls.
Accordingly, some 50 of the early motor cars were given suitably imposing names, either by Johnson or by their proud owners. In an inspired moment, Johnson dubbed the twelfth chassis, number 60551, the ‘Silver Ghost’, in homage to its almost supernatural quietness and smooth ride. Painted silver and adorned with silver-plated fittings, it was widely exhibited by Rolls-Royce at motor shows, and Silver Ghost would go on to become the name by which the 40/50 H.P. was generally known, as it is today.
But chassis 60551 was more than just a showpiece. Out on the road, it dominated the gruelling, high-profile reliability trials that represented the pinnacle of motoring endeavour at that time and were thus central to Johnson’s relentless promotional activities. In the process, it perhaps did more than any other early Rolls-Royce model to establish the marque’s international reputation for performance and engineering excellence.
Its extraordinary run of success began with the 1907 Scottish Reliability Trial, in which it covered some 2,000 miles without a single breakdown, the only delay being for a minute to re-open a closed fuel tap. Immediately afterwards, it covered 15,000 miles non-stop, driving day and night except for Sundays, setting a new world record for continuous travel.
In 1911, impelled by his own pursuit of perfection and Johnson’s insatiable appetite for publicity, Royce unveiled a new version of the Silver Ghost. Known as the ‘London to Edinburgh’ type, it was designed for the RAC’s flagship reliability trial, a return run of almost 800 miles between the two capitals. In an age long before motorways, the route consisted almost entirely of poorly surfaced A- and B-roads; to add to the challenge, cars were locked in top gear from start to finish.
Chassis number 1701 won the event at an average speed of 19.59mph, returning a then-unheard-of fuel efficiency of over 24 mpg. To prove it had not been modified in any way, it achieved 78.2mph on a half-mile speed test conducted soon after the Trial; later that year, fitted with a lightweight streamlined body, it attained 101.8mph at the fabled Brooklands circuit in Surrey, becoming the first Rolls-Royce in history to exceed 100mph.