On the move: Supercharged BMW WR 750

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On the move: Supercharged BMW WR 750
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On the move with the BMW WR 750

Ready-to-drive replica

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The supercharged BMW WR 750 broke championships and world records in 1929. The originals are lost, but now there is a ready-to-drive replica.

The fame for the idea of ​​increasing the performance of BMW motorcycles by charging goes to the engineer Rudolf Schleicher; however, he could not implement them in Munich. It is no longer known whether it was the principal objections of the then chief designer Max Friz or the high expenditure. In any case, Schleicher switched to the car manufacturer Horch in Zwickau in 1927. Racing mechanic Sepp Hopf, Schleicher’s closest confidante, and Ernst Jakob Henne, the works driver and German champion in 1926 and 1927, continued to pursue the idea. Henne had set the absolute speed record as a goal and saw the supercharging of the engines as the only way to achieve this goal. Even after Schleicher’s departure, the experiments continued, from 1928 with Friz’s official approval; two motorcycles were created.

1In 929, BMW presented the completely new machines with a modified frame, new brakes on the front and rear wheels and the new supercharged engine as the centerpiece. The five best results from eight runs counted for the German championship. The motorcycle racing department’s most elaborate development up to that point raised high expectations and the press showed great interest in the racing motorcycle. To what extent the political currents of that time are reflected in the language, everyone can judge for themselves.

At the third championship run, the Marienberger Dreiecksrennen, the supercharged BMW made its debut under Ernst Henne; the magazine “Das Motor-Rad” reported: The third run was the Marienberger Dreiecksrennen, the fastest road race in Germany. In the largest class, Bauhofer-Munich won B.M.W. one of his great victories. He set the best time of the day with a new record. Behind him came Stelzer, who thus held the lead in his class. In the 500 class Soenius-Koln had to go to B.M.W. Retired lying down in a promising position due to tire damage. Zundorf on DKW and Henne on B.M.W., the new world record man, took first and second place.

The sixth run of the season was supposed to take place on the Avus for the big classes, but was moved to Kolberg due to construction work: Soenius was able to book his first points here, even if it was only a fourth place. Stelzer did not start in the big class and Bauhofer won again with the best time of the day. In the 500cc class, 12 out of 18 machines fell victim to racing bad luck. Bauhofer’s unheard-of pace was to blame. He tore everyone out and the chase behind him dropped drivers and machines like flies. Even Henne couldn’t keep up with his pace – only Stegmann was up to him. He drove on the new Kompressor B.M.W. 15 seconds behind Bauhofer on the 50 percent larger machine and was even able to set the fastest lap with 106 km / h. book for yourself.
But bad luck pursued him and the other drivers equipped with Zoller compressors. Henne was eliminated in the 5th lap due to a broken gearshift fork, while Soenius and Stegmann disappeared from the theater of war on the second to last and last lap from the safest top position – almost in their pocket. According to the B.M.W.principles, nobody knew what happened to them. Whether the motors could not cope with the overload caused by the compressors or whether other defects occurred. Nevertheless, the race had proven that the B.M.W. compressor machines were far faster than all the others, and the B.M.W. racing team is looking forward to the grand prize at the Nurburgring with great confidence.

In the summer, the championship took place in Swabia, and BMW was able to record successes here: The 7th of July then brought a major battle day at the Solitude, which saw the Munich stilt on BMW as the overall winner and Soenius-Cologne as the class winner. Soenius took his first victory in the most important 500cc class. In the 750 cc class, Bauhofer did not start because of a training accident, Stelzer won with the best time of the day.

The 1929 season


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Vane loader of the BMW WR 750

On the occasion of the German Grand Prix on July 28th, Das Motor-Rad, issue number 32, commented on the supercharged motors rather skeptically: The Bavarian engine works had risked a lot when they equipped their 6 factory machines with Zoller compressors. Overcharging creates additional stress that not every engine can handle, and yet there was not a single engine failure during the entire race. The most important question of the day was whether the 750 cc machines are faster than the famous British with their 500 cc machines. So much for the bad luck that B.M.W. developed, allows a conclusion. the question can be answered in the affirmative. Soenius, who had started 2 minutes before the English, was in the front for 10 laps without being able to get close to him. The distance had already narrowed to half a minute, but Soenius hadn’t got the last of his machine out of the way. He could go even faster, as demonstrated by a short gallop when he had lost time on refueling.

However, whether he would have succeeded – if magnetic damage had not thrown him out of the race on the eleventh lap – in the final battle to fully utilize the excess power of his engine without a crash and thus to usurp the fastest time of the day is of course a question that cannot be answered. But the answer would be of the greatest interest, because it depends on whether it is at all expedient to increase the engine output with compressors or whether the machines already have an output that is at the limit of what the driver can control.

At the time, no one could have suspected that 40 hp and a vehicle weight of 160 kg would at best knock a beginner off his feet in 2007. In any case, racing was hardly impressed by this discussion: The real interest was of course concentrated on the 500 cc class, in which Bayerische Motoren Werke had sent 4 drivers. Stegmann had worked his way up to the English more and more. His performance must be rated all the more highly as he was the only one left of the entire B.M.W. stable. The slightest carelessness must be devastating. That he was still driving at 100 km / h. Average of just 5 minutes behind Tyrill Smith in third place, cannot be rated highly enough.

In September the championship season was approaching its decision: At the race on the Nurburg-Ring on September 8th, the class 500 and over 500 cc of the championship were rated. In the largest class, none of the previous contenders started in this race as well as in the Schleizer Dreieck, so that Stelzer could no longer be caught. In the 500 cc, however, a fierce battle broke out, so that the duel between Soenius and Klein was eagerly awaited. Soenius with his Kompressor-B.M.W. but was faster on the straight, Soenius won the race with the best time of the day and an hourly average of 115 km / h. probably the fastest time that has been driven on the Sudschleife so far.

Before the last championship run in Schleiz, BMW drivers Stegmann and Soenius as well as DKW driver Klein were tied at the top, which promised an exciting race: Stegmann performed on his Kompressor-B.M.W. start the race in brilliant style. He had no competition. But the tatters are flying off Stegmann’s rear tire. The coat is falling apart, as it was on the Nurburgring. Yes, yes the tires! Just don’t look at them too optimistically. Along with spark plugs, they are still the motorcyclist’s eternal problem child. Stegmann is carefully waved off from the depot before a disaster can occur.

But the excitement of the race is not over yet. Soenius 500 compressor – B.M.W. is hardly much faster than Klein’s water-cooled DKW. You fight for the championship title, it’s a matter of seconds. Klein has to refuel and that is the end of the fight. Soenius ’B.M.W. pulls him away and after an extremely exciting fight can win the cup of the city of Schleiz, with the best time of the day and with it the championship.

World records


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BMW WR 750.

Hans Soenius and Josef Stelzer were the names of the German champions of the 500 and 750 classes. The English were approached internationally, but they were still ahead of the curve, especially on winding courses. Ernst Jakob Hennes’ first world record in September 1929 proved that one was on the right track with the supercharger motors. At 216.75 km / h, he outbid the Englishman Herbert Le Vack by almost 10 km / h. The 1930 season got off to a promising start, BMW competed in the European Championship: Karl Stegmann achieved two victories at the Eilenriede and the Hungarian Grand Prix. But then fate struck: Stegmann, a BMW works driver since 1929, had a fatal accident while training for a hill climb. When Karl Gall, the second works driver, had a serious crash in Rome and at the Nurburgring, BMW took the works team out of racing.

In 1931 Schleicher returned to BMW as a test manager for automobile development. The further development of the supercharged racing machine was initially slow. The relatively high weight of the entire drive in connection with an aging chassis concept meant that the competing models were more agile than the BMW. BMW was able to boast once again when Josef Stelzer won the German Grand Prix on the Avus in 1933 with a new course record (166.5 km / h) and a lead of over three minutes. On the same route, Henne achieved an average speed of 204 km / h on a demonstration lap with his world record machine.

It was the last major appearance of this engine. The development of a new factory racing machine had long since begun under Schleicher’s direction. From then on, the WR 500 and WR 750 served as test vehicles, for example in the development of the telescopic fork. In 1935 BMW presented the new vertical shaft works racing motorcycle type 255; Schleicher and his team had dared a radical cut. With this new vehicle, BMW set itself at the forefront of international motorcycle racing and achieved many successes for which the first generation of supercharged motorcycles had laid the foundation in previous years.

Today the chassis surprises with its stability and handiness. The WR 750 was available as a short and long version, the wheelbase of which differed by 50 mm. The short version driven by MOTORRAD CLASSIC can be easily steered on narrow courses such as hill climbs and is completely stable on the Nurburgring-Nordschleife at top speed (approx. 175 km / h). Even the brakes decelerate properly, which is all the more astonishing given the fact that the vehicle was driven on unpaved roads and pavement in the 1930s.

The performance characteristics can almost be compared with those of a turbo engine: the charger delivers little pressure below 3000 to 3500 rpm, the engine works largely as a vacuum. At higher speeds, the vane compressor puts the engine under heavy pressure, and the WR then marches forward vehemently, although today the compressor only builds up 0.4 bar boost pressure for reasons of stability. During her active days, the boost pressure in the race was 0.8 bar, in Ernst Hennes’ world record it was even up to 2 bar, which was good for up to 95 hp.

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