Well, with the Bergspyder it was not so much what it did, as what it was. Which is the lightest racing car Porsche ever produced, and I suspect just about the lightest car of any kind produced by a mainstream manufacturer. It weighed just 384kg and if you want that put into some kind of perspective, the absurdly lightweight Lotus 48 that was its contemporary in Formula 2, had a smaller engine and was the work of lightweight obsessive Colin Chapman. And it weighed 420kg.
And it was the extent to which its creator, Ferdinand Piëch (who would follow the Bergspyder with the 917 and then become arguably the most influential industrialist in the car industry), went to reduce its weight that provides the fascination.
I’ll start with the basics. There wasn’t much he could do about the 2-litre flat 8 engine, which was derived from the 1962 F1 car. But it didn’t need an alternator because even a small battery will provide enough sparks to get a car up a short hill. It had a spidery spaceframe chassis as you might expect, but with aluminium rather than steel tubes. On this was draped polyester bodywork that was in places less than 1mm thick.
Then Piëch got really clever. To negate the need for a fuel pump, he put just 15 litres of petrol in a bag and encased that bag in a titanium shell, pressurised with nitrogen which would squeeze the bag and force the fuel into the engine. What very little wiring was made not from copper but silver thread of all things. The springs were titanium, not steel.
But it is the brakes that revealed just how crazed was the quest to save every gramme. Piëch realised that if he made the discs from beryllium rather than cast iron he could reduce their weight from 3.2kg per corner to 848g, saving almost 10kg of unsprung mass, an incredible gain for such a light car. And because the car was so light and used for hillclimbing where gravity already tended to help out in the braking areas, the thermal loads could be kept with tolerances too. Great. There was only one drawback, and it was not the exorbitant cost of beryllium, but the dust it gave off when stressed. Calling it poisonous is putting it mildly: today it is ranked as a class one carcinogen alongside such delightful substances as asbestos, mustard gas and plutonium. And even that didn’t stop Piëch.