Roger, two references:-
1: He [Jean Bugatti] frequently tested the company's prototypes. On 11 August 1939, while testing the Type 57 tank-bodied racer which had just won a Le Mans race, not far from the factory on the road near the village of Duppigheim, 30-year-old Jean Bugatti was killed when he lost control of his vehicle and crashed into a tree while trying to avoid a drunken bicyclist, who had gotten onto the track through a hole in a tree
2:After the 1937 victory, Ettore Bugatti stated that he wouldn't return, until his record of that year would be improved. In 1938 a Delage took the victory, however, at a lower average. Jean had to convince his father, but Bugatti would participate only under the following condition: Only one car was to be entered: "As there is never more than one winner, one car only must be enough."
One car only, against all the others, doesn't seem much. There were six Talbot's. three of them of 4.5 litre, 8 Delahaye's (six 135MS), two Delage 3 litres, a majestic Alfa 2500SS coupe driven by Sommer, and two Super Lagonda V12 4.5 litres, designed by a certain W.O. Bentley.
Entered was a Type 57C, different from the 1937 model, although similar in appearance. This time it was a supercharged car, based on a normal touring frame (not on a T57S chassis.). Although the frame was a classic one, the body, weighing not more than 60 kg, was improved still, together with the Piano-wire wheels of the T59 a very beautiful combination. The brakes are hydraulics and amply ventilated, behind the bonnet there are air extractors, at the sides of the body.
However, in the beginning of the second practice session, the engine breaks down. Wimille, Veyron and Jean Bugatti are thinking about giving up. Not Robert Aumaître though, the chief mechanic. Molsheim is called, and 8 new pistons are brought to Paris, with an Autorail (of Bugatti design, naturally). Here Le Grand Robert is waiting in his T57, to take them to Le Mans. With the help of a local metal worker the block is made ready for the new pistons. On Saturday all is cleaned, the pistons mounted and all is ready for the start!
During a rapid test, the engine doesn't seem to good, the competition is going to take advantage of that. Louis Gerard in his Delage takes the lead, Sommer is out, and Wimille and Veyron follow, not without problems though, the engine overheating. Even the inside wings had been removed, risking disqualification. A wheel breaks, and Wimille goes from 4th place back to sixth! Sunday, at the end of the morning, Gerard is 5 laps ahead of the Bugatti. However, at the beginning of the afternoon all is going to change. The Delage is making more and more bizarre sounds, and has at least two valve springs broken. At 13h00, the Bugatti is two laps ahead! There is another one won! Although Mazaud in a Delahaye has taken almost a second from Wimille's 1937 record.
Jean Bugatti claimed afterwards that the bonnet was never opened during the race, and that a top speed of over 255 km/h was attainable.
rgds
Do we know that? I've no evidence but there would be some logic in using a short wheelbase for racing but calling it a T57C as the S was out of production. It's unlikely that any one measured the car before Jean Bugatti's accident.
I would guess that the S stood for Sport.