Started racing motorcycles but switched to cars. He became a Mercedes test driver in 1932 and drove in a number of Grand Prix in 1934 and 1935. He crashed badly in the Swiss GP in 1935. He recovered and returned to Mercedes as a timekeeper and assistant team manager until 1955.
Geier started racing motorcycles in 1920 when he was 18. Later he switched to racing cars, first with an Amilcar and later Bugattis together with Bubi Momberger, who joined the Auto Union team in 1934. Together they drove in the first race ever on the Nurburgring, winning their class.
He was friends with Gretal Schwab but when she offered to arrange for him to test for Mercedes, he did not believe her and instead went to work as a salesman for F. K. Mettenheimer in Frankfurt, selling American cars.
In 1932 he did become a Mercedes test driver, working on the supercharged 3.8 litre Cabriolet, and in 1934 he got his chance as a Grand Prix driver. He was demonstrating the 500K when he received a call from Unterturkenhein to leave the car where it was and to travel to the Nurburgring for the German Grand Prix as von Brauchtitsch had broken his arm in a crash. He practiced in the ex-Caracciola Monza Alfa and then in the race drove the Mercedes W25 finishing 5th. He was signed as reserve driver for the rest of 1934 and for 1935.
His first race in 1935 was in the streamline Mercedes with the enclosed cockpit, which had been used the previous year for World Speed Record attempts. He failed to finish in the final and the car never raced again in that configuration much to the delight of Geier as the canopy could only be opened from the outside!
His next race in 35 was the Swiss Grand Prix at Bern. Geier crashed badly in practice after loosing control at 150 mph (240 Kph) coming out of the curve before the pits. The corner was banked and Geier, who was flat out, was running too high. The tail of the car broke away; hit a wooden fence in front of the grandstand.
Geier fought to control the car but it crossed the track and hit a large tree breaking into four parts. The front of the car ended up on the opposite side of the track. The cockpit and centre section of the car lay in the middle of the track. The engine was neatly deposited on the grass verge along with the rear section of the car.
Geier was thrown out and ended up under a car in the car park! He suffered terrible injuries. Incredibly there was no ambulance and Geier was taken to hospital in the sidecar of a motorcycle combination with the Mercedes doctor, Dr Glaser, riding pillion and administering to the stricken Geier!
He broke both legs, one ankle, his shoulder and the base of this skull. His spine was damaged and he was unconscious for eight days but amazing he survived. He spent four months in hospital.
On his release he returned the Mercedes team, not as driver but as a timekeeper and assistant team manager to Herr Neubauer until 1955.