Bertelli, a racer at heart and with considerable competition experience, was keen to promote his Aston Martins in as many national and international events as he could, and this of course included the most prestigious event of all: the Le Mans 24 Hours Race. The works’ racing cars were therefore given the prefix ‘LM’ to distinguish them from production cars.
Parts to build the works cars were chosen very carefully from stock and then often modified to lighten them. The front axle, a very heavy forging, was carefully machined on all faces, including around the kingpin eye, to remove a total of 6 lbs. of metal. Stub axles, kingpins, steering box brackets, rear spring shackles, bulkheads and many other small components were drilled or machined to make them fractionally less heavy. Parts were also re-made in lighter materials, for example aluminium replacing bronze, or ‘Electron’ (a magnesium and aluminium alloy) replacing aluiminium. Where possible, parts were improved, and these modifications were often later to be found on production cars. For example, the width of the brake shoes was increased from 1⅛" to 1½" on the racing cars and from a single pivot shared by both shoes, to a pivot for each shoe; a design to be seen on the 1933 ‘Le Mans’ and the Mark II until the 1936 ‘15/98’ 2 litre.
Gearbox and rear axle worm and wheel ratios were also selected and carefully tuned to the expected output of the engine to maximize top speed. Different gearbox ratios were tried in different cars, with long first gears and close ratio second and third gears. LM3 had a third gear that was only a few hundred revs different to fourth gear, enabling very swift changes from third to top and back again.
The later cars, from LM4 onwards ran on 19" wheels, which further allowed final drive ratios to be adjusted. This was particularly important at Le Mans were the circuit was little more than three very long straights connected by three sharp corners.
Engines were very carefully assembled and tested in the racing department. Having their own test shop and dynamometer meant that many different components could be tested on the engines, and a number of different cams and carburettor settings could be tried out to maximize power and torque. Engine output for the team cars was probably about seven to ten percent higher than a production engine, and this combined with the lighter chassis and bodywork meant that the LM cars had a significant advantage in performance over production cars and they were certainly competitive within their class.
With his previous competition experience and with growing confidence in his new sports car, Bertelli developed two works racing cars for the 1928 season; LM1 and LM2. With lightened components throughout, lightweight Harry Bertelli three seater coachwork and with the dry sump engine now giving up to 63 bhp they were immediately competitive. Lessons were quickly learned by Bertelli as the rear axles gave trouble on the way to Le Mans and had to be modified. So, the pattern of developing and improving the new Aston Martin through experience gained by racing his cars had been started, a trend which Aston Martin continued right through to 1939 and the outbreak of war.
Two further team cars were built in 1929 and 1930, LM3 and LM4. Both were raced at Brooklands in the "Double 12" (Bertelli’s favourite race) and both at the Irish Grand Prix. LM3 was also raced by the works at the RAC TT at Ards in Northern Ireland, where it crashed on the first corner and later retired. This car was subsequently re-bodied with a stub tailed two seater ‘Sports Model’ body and used as a works demonstrator and re-bodied in 1930 with a long tailed racing body and further raced by the works. It was re-bodied yet again in 1932 and sold as ‘Four Seater "International" Sports’.
The later first series works’ team cars, LM5, 6 and 7, had the rather inefficient Renwick & Bertelli cylinder head modified into four separate inlet ports matched to a much better designed inlet manifold. With 1¼" and later 1⅜" carburettors fitted, a considerable power advantage was gained over the standard engine. Racing timing gears were straight cut and heavily drilled and only two thirds the width of the production helical gears. Even the countershaft which carried the intermediate timing gear was taper bored to reduce weight.
Harry Bertelli, who built the coachwork for the works team cars, also played his part. Light weight ash body frames were built with simple and lighter gauge panels attached. The racing cars were used to experiment with bodywork, and different methods of mounting the wings - not always successfully - were tried. Bonnets and spare wheel mountings changed almost from car to car.
The 1931 cars, LM5, 6 and 7 had at least two methods of securing the wings. First with a relatively simple ‘blacksmiths’ wing stay for Le Mans which, having already had a pounding at Brooklands for the ‘Double Twelve’ race were found to be wanting. Then for the TT, a heavy cross tube was fitted in front of the radiator and the top of the front wings attached to it. The method of getting to the spare wheel was also changed from race to race with these three cars, a good example of Bertelli’s own racing experience directly affecting design. Originally, the spare was extracted from the rear of the body tub by folding down the front seats. However when it was realized that that bucket type seats were preferable and needed to be tightly secured to the floorboards for driver comfort and stability, this was no longer possible. So, a large aperture appeared on the rear of the tub for the TT, covered in canvas, through which the spare could easily be reached. LM7 later had the spare mounted on a simple frame on the off side of the car and a luggage compartment built where the spare had been, with a paneled lid. Only the bodywork of LM6 survives to this day in its original (TT) form, but curiously with the Le Mans type wing stays.
Team car radiators, (heavy components stuck out well ahead of the front axle) were reduced in height as much as possible similar to the earlier ‘Sports Model’. This not only reduced the frontal area of the car, but also the weight both from the radiator itself, and by virtue of the smaller volume of water held, no doubt contributing to a slight decrease in ‘understeer’. This was the handling characteristic of most vintage cars and particularly so if you had the best part of two gallons of oil in a tank at the very front of the car. Oil tank capacity was increased for the racing cars and stone guards were fitted to protect the tank and its contents.
Many of the team cars had more than one set of bodywork. Both LM1 and 2 were quite quickly re-bodied and their appearance smartened up to serve as demonstrators for the works. LM3 had four different bodies in three years, including one of the stubby tailed 2 seater bodies and later a more conventional ‘International four seater’ coachwork. This particular car was over-stamped (literally) with another chassis number and sold through the works, almost as if it was a standard car. LM5 was also re-bodied with 2/4 seater coachwork with dramatically humped scuttle. Two more identical bodies were fitted on two of the ‘International Le Mans’ models and to a certain extent these cars were the prototype for the later 1933 ‘Le Mans’ bodywork.
No wonder the motoring press found the Aston Martin an excellent car, what they were testing were often thinly disguised works racing cars. Those works cars that were not retained as demonstrators were sold to the public or in some cases to ex works’ drivers. They were often independently wealthy young men and owning a works racing car would have been as exciting then as it would be now. In this vein, LM7 was sold to ‘Mort’ Goodall who campaigned it at Brooklands and in all the major rallies in the UK and at the 1933 Le Mans.