That 1937 car was the famous W125, meticulously developed by Uhlenhaut to take on the Auto Unions. He did thousands of miles testing at the Nurburgring Nordschleife.
During one test he lapped three seconds quicker than Fangio, and admitted that: “I can drive rather fast.” That was about all his modesty would allow. He also was quickest in testing at Monza, but racing never appealed to the engineer. However his driving skills benefitted the team as a whole as he could translate personal his feelings into improvements.