Mercedes-Benz and Auto Union were rivals not only on the racetrack. The two German brands fought to assert the supremacy of their cars in record-breaking attempts as well. The cars used by Mercedes-Benz were derived by the Stuttgart engineers from the Grand Prix cars. A version of the W 25 with aerodynamic cockpit panelling made a start in 1934.

Alfred Neubauer reported on the record-breaking attempts in Hungary: "It's October. A cold, wet wind is blowing on the expressway at Gyón, south of Budapest. We fear this wetness, this wind. Because we want to capture world records." Rudolf Caracciola sat at the wheel of the record-breaking car. "Rudi is driving, and for the first time in his life he is doing more than 300 kilometres per hour. Faster than any human being ever has driven in a conventional racing car on a road. Caracciola is setting world records. This is his greatest victory this year."

Caracciola underscored the performance capabilities of the 430 hp (316 kW) racing car by setting international records in class C (3 to 5 litres displacement) over one kilometre (317.5 km/h) and one mile with a flying start (316.6 km/h). He also managed a new world record of 188.6 km/h for one mile with standing start. In December 1934 Caracciola additionally set an international class record (class C) of 311.98 km/h over five kilometres on the Avus course.

The W 25 also was the basis of the record breaker with which Mercedes-Benz gave a foretaste of the innovative potential of the new W 125 in 1936: on 11 November Caracciola established five international class records and one world record on the "Reichsautobahn" Frankfurt – Darmstadt in a Mercedes-Benz streamlined record-breaking car featuring a twelve-cylinder engine. The 1936 record breaker was completely faired. The aerodynamically perfected body even included the wheels and the underfloor. Developed in the wind tunnel of the Zeppelin works in Friedrichshafen, it had a sensationally low drag coefficient of 0.235. A V12 with 616 hp (453 kW) and a displacement of 5577 cubic centimetres delivered the power. The world record set by Caracciola was 333.5 km/h for the ten miles with flying start; his top speed was 372 km/h.

Another spectacular product of the wind tunnel, this time the one belonging to Deutsche Versuchsanstalt für Luftfahrt (German Aviation Research Laboratories) in Berlin-Adlershof, with a drag coefficient (Cd) of 0.157, was the 1938 record variant of the W 125. With it, on 28 January 1938 Rudolf Caracciola produced records for public roads which have held to this day: 432.7 km/h for the kilometre with flying start and a top speed of 436.9 km/h in one direction. Attempting to break the records a few hours later, Auto Union's star driver Bernd Rosemeyer lost his life: travelling at full speed, his car was struck by a gust of wind that pushed it off the autobahn.

The W 125 was propelled by the latest evolutionary stage of the 5.6-liter twelve-cylinder engine. Two Roots blowers boosted its output to 736 hp (541 kW) at 5800 rpm. A preliminary version of the 6.25-meter-long record vehicle tended to loose ground contact at 400 km/h. That was why Rudolf Uhlenhaut minimised the frontal area, thereby reducing the radiator's flow resistance. Just two small nostrils supplied intake air to the huge V12. Optimal working temperatures over the short distances in question were looked after by the conventional radiator of the W 125, embedded in a chest filled with half a cubic meter of water and ice and resting on two supports in front of the engine.

In 1939 specialisation had made such advances that two record-breaking versions for class D (two to three litres displacement) were developed from the contemporary
W 154: one car for the flying start records (398.2 km/h for the kilometre, 399.6 km/h for the mile) and another variant with faired wheels and a characteristically notched section in the cockpit for the standing sprint (175.1 km/h for the kilometre, 204.6 km/h for the mile).

The record version of the W 154, developing 468 hp (468 kW) at 7800 rpm, was largely based on the three-litre road racer, not least in terms of its chassis. As much of its weight as possible had been shed for its special assignment, the car tipping the scales at 949 kilograms (without driver). An ice-cooling system had been relocated to the rear axle and thereby also improved traction. There can be no doubt that this record breaker looked the way a streamlined Grand Prix racer of the brand might possibly have.

Quite the opposite was true of the 8.24-meter-long T 80 of the same year, designed by Ferdinand Porsche in order to annihilate the existing world record of 484 km/h established by Malcolm Campbell. It was armed with the DB 603 RS aircraft engine, an 807-kilogram V12 generating a massive 3500 hp (2574 kW) from 44,500 cc at 3640 rpm. However, the T 80 was never used. With the beginning of World War II, history had other priorities to set, and there was no more room for speed records. Today the T 80 is displayed in the Mercedes-Benz Museum.