The Bristol 450 was a successful sports car racing prototype model, designed in 1953 by Bristol Cars and based on the abortive ERA G-type Formula Two car of 1952. Although most sources state that only three 450s were built, photographic evidence suggests that at least four were in existence at one point in time. The cars were constructed specifically to contest the prestigious 24 Hours of Le Mans endurance race, at which they won both their class and the team prize in both and . In addition to its race victories, the Bristol 450 also took a number of outright speed records for the 2-litre class during trials at the Montlhéry circuit in 1953. Following the 1955 Le Mans disaster, which killed Pierre Levegh and 83 spectators, Bristol withdrew from direct involvement in motorsport and all but one of the 450s were broken up.
Design history
The fundamental design of the Bristol 450 was laid down by Robert Eberan von Eberhorst, and completed by his protégé and successor David Hodkin, as the chassis for the ERA G-type Formula 2 car, Leslie Johnson's attempt to resuscitate the ERA name in 1952. The G-type was initially planned to run using a custom built ERA engine, but when funding became a problem the design was adapted to incorporate the popular Bristol straight-6 engine, also used with some success by Cooper, Frazer Nash and AC. However, engine modifications made by Hodkin resulted in engine failure in all three of the G-type's Grand Prix outings, despite being driven by rising star Stirling Moss. At the end of the 1952 season, out of money and in failing health, Johnson sold the project to the car manufacturing arm of the Bristol Aeroplane Company.
Chassis and running gear
In late 1952 Bristol made the surprise announcement that the car was to be redesigned as a two-seat sports car, for entry into the following year's Le Mans race. Over the following few months the G-type was comprehensively redesigned and rebuilt by Bristol's new motor sport department, with the design team led by David Summers. The chassis itself was founded on twin, oval-section rails running the length of the car, which were changed to simple circular-section members for the Bristol. To these, the G-Type's double wishbone front and de Dion tube rear suspension were attached. The wheelbase was relatively long at 8 ft 1¼ in (247 cm), especially considering the car's narrow track of 4 ft 3 in (130 cm). Inboard brakes at the rear and an innovative hub/rim arrangement reduced unsprung weight. These innovative wheels consisted of a large hub spider – through which driveshafts could be switched without needing to remove the wheels and brakes – to which a wheel consisting of little more than a rim was attached. For the 1955 Le Mans race, to save further time during pit stops, Bristol developed an equally innovative multi-barreled, powered spanner, which could remove all five wheel nuts simultaneously. In much the same way as for modern Formula One wheel changes, the spanner would then retain the wheel nuts and allow precise reattachment of the new wheel to the car, applying the correct amount of torque to each nut.
The tall Bristol engine was mounted forward in the chassis, with drive passing along a propshaft directly under the cockpit to the four-speed gearbox mounted behind the driver. This arrangement, while requiring precise balancing of the engine-speed shaft, meant that weight distribution was as even as possible. Fuel was carried in two pannier cells behind the front wheels, in the position that Bristol road cars traditionally have battery and spare wheel compartments; their central position also resulted in minimal disturbance to the handling character of the 450, whether running on full tanks or empty. The sweet handling of the resulting car was commented on by driver Lance Macklin, when he stated that the Bristol 450 "could be driven without hands".
In early 1954, modifications were made to the engine that raised power output from the original ~140 bhp to , raising top speed to over with Le Mans gearing. With a kerb weight of only 1450 lbs (658 kg), the power-to-weight ratio was over 235 bhp/tonne, comparable with many modern high-performance sportscars.