During a practice session, Fangio ( the reigning World Champion) returned to the pits and complained to the team that his Mercedes-Benz W196 (or 300 SLR) was not set up properly and was behaving poorly on the track.

Uhlenhaut (driving engineer for Mercedes-Benz, and the father of Mercedes-Benz 300 SL) fresh from an executive lunch and still dressed in a full suit and tie, climbed into Fangio's race car.

 He went out onto the notoriously demanding Nürburgring and turned in a lap 3 seconds faster than the reigning World Champion's time.

 "the gentlemen should practice more" was his comment afterwards...

https://petrolicious.com/blogs/articles/the-mercedes-engineer-that-was-too-good-to-race

all stories like this should be gathered in one book, about the funny things said and done in the racing world for the past 120 years