Railway rolling stock is heavily engineered and in the 1930s was growing heavier and heavier with each new locomotive and coach built. The contact surface between wheel and rail is quite small, and it needed the weight of the locomotive pressing down on its wheels to provide the tractive effort. If you could achieve the necessary traction and tractive effort with a lightweight train there would be huge cost savings.
A promising development was the use of rubber tyres for railway wheels. In France, at Clermont Ferrand, the two Michelin Brothers, André and Edouard, were very enterprising and always looking at ways to build up their tyre business which they had founded in 1888. This included their hotel guides, and road maps, to encourage cycling and motoring and therefore use more tyres. Trains were by a long way the main transport mode, and so if they could run on rubber tyres it would be a great boost to them. They set about developing a light rail vehicle in 1927. Pioneering work had been carried out in the USA and in 1923 several subway systems introduced rolling stock with light metal roofs, doors, interior fittings, buffers and so on. Then aluminium bodies were being made, and in Switzerland, aluminium parts and components.
Rust proof metal sheets had been used to cover the roof and sides of wooden bodied rail vehicles, such as on the SBB’s only narrow gauge line, the Brunig Bahn and in the 1940s became more widely used. The concept was developed to chassis-less coach bodies. The change to aluminium and alloys brought difficulties, as at that time welding such materials severely weakened them, so load bearing parts were riveted and non load bearing parts spot welded. Heavy duty parts, such as the draw bar, bumper frame, pivot bearing parts etc., were still made of steel and screwed or riveted to the body. SIG used these methods to produce a 20 m long coach body weighing just 3,250 kgs (of which 1,000 kgs were steel),compared to 10,400 kgs for a 21.4m long “normal” coach body.
There were, of course, a great many engineering problems to overcome with using rubber wheels. The friction between a rubber tyre and a steel rail is three times that of a steel wheel on a steel rail, so only one third of the former adhesion weight is needed to obtain the same tractive force. This force would also be considerably reduced if lightweight construction materials and methods were used, and also, only light and economical motive power units would be needed. Rail wear would also be considerably reduced, and the rubber tyres do not give any hammer blow to rail joints. In addition, the trains would be quieter and give a smoother ride.
A lot of work was carried out and prototype railcars tested. The first prototype was a Renault lorry on four rubber wheels, which was tested only in the factory in October 1929. In January 1930 a 40 hp Renault lengthened to carry a third axle was tested on the mountainous Laqueville – Mont Dore line. In October 1930 a railcar with a two axle motor bogie at the front and a bissel axle at the rear was run. Finally, on the 26th of January 1931, Michelin went public with the first official run with a 20 hp Panhard car with narrow pneumatic rubber tyres, fitted with dished steel plates behind the tyres to act as wheel flanges to keep the vehicle on the rails, which was shown to the press and public.
The first recognisable railcar with 18 seats was tested by André Michelin on the St. Florent – Issoudun line, of the Orléans railway company. In the summer of 1931 a three car train of Michelines ran frequent tests between Coltainville and Saint Arnoult on the Est railway. On the 10th of September 1931
