The memorable Lotus Eleven is often thought to have been the inspiration for the Lotus 15 design. In some respects, this was the case. The Fifteen was a more modern version, with a front-engined layout and a very sleek design. However, the design was created by Williams & Pritchard, and not Frank Costin. So there were differences between the two, though at first glance they may seem to have been cut from the same mold. The Fifteen was only 24-inches high. The driver was just a few inches off the ground and sat very close to the rear tires. The wrap-around Plexiglass windscreen was the same height as the rear decking. The driver's were still encouraged to wear eye protection, as the windscreen did not adequately protect the driver's face, and they often looked over it, rather than through it.
The Fifteen did borrow technology from the Eleven, which was appropriate given the Eleven's racing success and proven capabilities. The Fifteen rested on a space-frame chassis built from 1.75-inch square and round tubing, using 18 and 20-gauge steel. The front suspension of the Eleven was incorporated into the Fifteen, using upper wishbones and coil springs with damper units. In the rear was a strut suspension setup.
The steering was a rack-and-pinon setup. There was a 19-gallon fuel tank which was more than adequate to complete many races without requiring a re-fill. The front 9.5-inch disc brakes were mounted outboard and the rear discs were inboard. The center-lock wire-spoked wheels measured 15-inches tall; the factory works cars were given special magnesium-alloy wheels. These special wheels were available to the customers, but for an additional price.
The fuel tank, spare wheel, and oil tanks were placed in the rear of the car. Power came through a variety of engines. The car had been designed to accept a variety of engines, ranging from 1475cc through 2495cc. The early versions of the car had the engine mounted at a sixty-degree angle to the right in an effort to reduce frontal area.
The Lotus 15 made its racing debut at Goodwood in 1958. The 1960cc Climax machine was piloted by Graham Hill who drove the car for most of the race before being forced to retire prematurely. A week later, the car was entered in the British Empire Trophy at Oulton Park where Cliff Allison was given an opportunity to try his luck with the newly created machine. The car did well, finishing First in Class in the 2000cc and About class. Hill had also been driving a Fifteen in this race. His day did not fare as well; he was again forced to retire due to mechanical difficulties.
Two Factory Team 15s were entered in the grueling 24 Hours of LeMans. The engines now were sitting at a 17-degree angle in the engine bay. The 2.0-liter car driven by Allison/Hill raced around the track for three laps and then was brought into the pitts due to a failed cylinder head gasket. The other car, powered by a 1.5-liter engine, was driven by Jay Chamberlain and Pete Lovely. This car did not make the full 24-hours either; it was crashed while in the hands of Chamberlain.
Part-way through the 1958 season, Champan introduced the Series 2 version of the Fifteen. The Series 2 had its transaxle replaced with a BMC Series B four-speed gearbox and the engine was tilted at a 17-degree angle. This was a less-complex version of the Fifteen, and intended mainly for export, and for privateers. The cars had mild success on the racing circuit. One of the more notable efforts was the car owned by John Coombs and driven by Roy Salvadori. It finished second overall at the British Grand Prix, and captured a victory at Gold Cup meeting at Oulton Park.
There were further improvements to the car for the 1959 season. In all respects, these were amazing machines, but there was mounting competition and teething problems to conquer before the cars true potential could be ascertained. The suspension was slightly revised which provided additional room for the installation of a larger radiator and oil cooler. A Fifteen driven by Allison during the 1958 season had encountered an unusual problem. The chassis had broken, locked up the steering, and nearly pushed through the front hood. To make sure this would not happen again, the chassis was strengthened for 1959. The front track's width was also reduced. These changes were enough to bring about the Series 3 name.
The Factory Works Series 3 cars had mild success. The Cooper Monaco cars were very strong competition and the Fifteen's found themselves outpaced on many occasions. Some success was had; Alan Stacey won 1500cc Sports Car Race at the British Empire Trophy at Oulton Park. Privateer Michael Taylor won the Grand Prix des Frontieres at Chimay in Belgium.
For the 1959 LeMans race, Chapman entered a 2495cc Fifteen driven by Graham Hill and Derek Jolly. The car ran well until gearbox problems began showing up. During the tenth hour with Jolly at the wheel, the car was over-revved and the engine failed. For the second year in a row, the Fifteen left the race without ever crossing the finish line.
In minor events, the cars did well when mechanical issues did not prematurely side-line the car. As the close of the 1950s came into sight, the Fifteens had become obsolete machines. Even with proper preparation and fine-tuning, it would have been hard to outpace the Cooper Monaco's and their mid-engined layout. The Lotus Fifteen cars were fast and competitive. They did experience their teething problems, but many were resolved and the car was able to provide podium finishes for much of its drivers. Part of the problem with the car was that Team Lotus had diverted much of its attention and talents to the single-seater series, so the proper attention was not given to fine-tuning the Fifteen.
