BRM's first attempt to bring Grand Prix success to Great Britain failed primarily because of the complexity of the V16 engine in the BRM Type 15. But it also failed because after much hype, and several years of development, the Formula One regulations were changed and the car was no longer eligible.
Five years after the Type 15's debut, work was finally started on a new Formula 1 car. Quite why BRM waited for so long to design a new car is anybody's guess. Perhaps they'd hoped that when Formula One returned, their old car might be relevant again.
Lessons had perhaps been learned. This time simplicity was the keyword, and the resulting BRM Type 25 (or P25) was certainly a much less complex affair.
Stewart Tresilian and Tony Rudd designed an entirely new twin-cam, 2.5-litre, four-cylinder engine for the P25. The engine's large bore allowed for larger valves to be fitted. The engine was mounted to a simple ladder frame steel chassis, with a centre tub monocoque section. The P25 used Lockheed disc brakes at the front wheels, which were later replaced by Dunlop discs. Uniquely, a single brake disc was fitted to the gearbox at the rear.
In September 1955 the Type 25 debuted in a non-championship race at Aintree. Producing some 275 horsepower it was relatively quick, but there were handling and reliability problems that would dog the car throughout its career. The big valves were a weak spot and the single rear brake was another major issue.
Three Type 25s were entered for Tony Brooks, Mike Hawthorn, and Ron Flockhart in the car's championship debut, the 1956 British Grand Prix at Silverstone. However, none finished. Flockhart's engine gave up on lap 2, Hawthorn's transmission packed in on lap 24, and Brooks had an accident on lap 39.
In spite of revisions to the car for 1957, reliability continued to be a problem. BRM did not manage a single finish at any of the championship events the team entered, namely Monaco, Rouen-Les-Essarts, and Aintree. To add insult to injury, Vanwall scored that elusive first British Grand Prix win in thirty years.
1956 BRM P25
After three years of development, the BRM P25 finally managed to achieve some respectable results. In 1958 Harry Schell and Jean Behra finished second and third at Zandvoort, Behra and Bonnier took fourth places in Portugal and Morocco, and there were a smattering of fifth and sixth place finishes. The BRM team ended the season in fourth place in the inaugural International Cup for F1 Manufacturers.
1959 brought further improvements to the car, and after a disappointing start at Monaco, Joakim Bonnier took the race victory at Zandvoort to register a first Formula One Grand Prix win for himself, the Type 25, and the BRM team. With further encouraging results elsewhere, BRM took third place in the International Cup for F1 Manufacturers.
The BRM P25 had finally developed into a fast and reliable racing car and a proven race winner. Sadly Cooper's mid-engined revolution meant that by the time the front-engined Type 25 finally came good, it was also becoming obsolete. Encouraged by the first win, BRM quickly developed a mid-engined version of the Type 25, using many existing parts from disassembled Type 25s. Other than the location of the engine and the driver, the specifications of the P25 and P48 were virtually identical.