For 80 minutes, Christian von Richthofen, who devised this peculiar musical comedy, and Rolf Clausen, his partner in crime, hurl themselves around the stage while vigorously smashing up an old car with sledgehammers, an angle grinder and, mostly, their bare hands, to produce a frantic percussive symphony.

It looks hard work, and von Richthofen has been known to exit the stage bleeding after attacking the car with too much theatrical gusto.

The problem at this sparsely attended Saturday matinée is that, no matter how much von Richthofen and Clausen toil and sweat, the audience just don’t seem to get it. Pretty soon, the beaten-up Rover 100 looks like a metaphor for von Richthofen’s bruised ego as he battles for a ripple of hesitant applause from a bewildered audience.

Even the Riverside Studios’ programme describes AutoAuto! as a “musical oddity”. The show, originally staged in Germany, is translated into English by von Richthofen and Mark Dolan, a British comedian. In it, the two German stars turn a car into a giant improvised drum kit. In between their musical endeavours, which range in style from Tchaikovsky to Motörhead via samba and hip-hop, they perform oddball sketches and cringeworthy jokes, doing nothing for the reputation of German comedy.

“To say a car is only fit for driving is like saying a chicken is only fit for laying eggs,” says Clausen by way of introduction, “but, of course, they make great lovers, too.” Cue total silence from the half-dozen squirming kids and parents in the front row.

AutoAuto! is not afraid of national stereotyping, either: comparing the difference between the sound of a door closing on a German, French or American car, the former is described as authoritarian – and the accompanying gesticulation is, if not quite a “Sieg Heil”, at least a clear military salute.

Seemingly unconnected sketches include one in which von Richthofen lies sprawled on the bonnet, reciting Der Reiter und der Bodensee, a 19th-century poem by Gustav Schwab. It ends with a line about being buried in “ein trockener Grab” (a dry grave), at which point Clausen places the Rover’s smashed-up windscreen over his friend, to simulate the lid of a coffin. Most of the audience gawp, gripped by a strange fascination for this incomprehensible spectacle.

It does gradually become gripping in its own peculiar way. Von Richthofen is a gifted percussionist and clearly some kind of mad, musical genius. There is no denying the skill and concentration required to create these intricate rhythmical soundscapes, energetically bashing, tapping, smashing, scraping and scratching to create a unique aural and visual experience. It is compelling to watch the pair throw themselves around, performing a mock ballet with their pickaxes, before unleashing perfectly timed blows to the Rover’s bodywork. And there is unbridled laughter when Clausen leaps onto the car’s roof to sing the opening of The Lion King, thanks to the absurd contrast between Disney’s sentimental musical and this unhinged explosion of dissonance.

Taking his bow, von Richthofen finally wins enthusiastic applause, then seals it with a well-timed joke: “Kids, don’t go home and try this on your own car – we recommend you practise on your neighbour’s first.” A gang of hoodies photograph the smashed-up Rover on their mobile phones as they shuffle out. Like them, I can’t help feeling a sneaking admiration for von Richthofen and Clausen. But as for what it is all about – beats me.

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