As concept cars go, the Audi quattro Spyder actually looked rather sensible. But then, Audi was a rather sensible company back in the early 1990s. What it needed was glamous and sexiness - no one was in any doubt the ability of its engineers to build a solid and capable car. So, what did the engineers and stylists do with its first serious crack at a mid-engined sports car? Yup, they made it appeal to the head and not the heart.

But that's the thing. The quattro Spyder was no mere concept car; it was conceived and designed with production in mind, sitting atop the range somewhere between where the R8 and TT do now. A prototype R4, if you like. 20 years ahead of its time.

In terms of engineering, the quattro Spyder was straightforward enough. Power was by the 100's new 2.8-litre V6, and the transmission was a modified version of the quattro's all-wheel drive layout. As for the chassis, it was a tubular steel affair, clad in aluminium panels. There were lift-out targa panels and the doors were conventionally hinged. In short, it was entirely production-feasable, introducing much of the aluminium technology that would become an Audi mainstay 20 years on.

The suspension setup featured trapezoidal links, which would late underpin the A4 range - and in this application resulted in great grip and poise during testing. When it was introduced - as a concept - to the public at the 1991 Frankfurt Motor Show, it was overshadowed by the more glamorous Avus concept, but it was greeted warmly by the press.

But despite the critical acclaim, Audi decided not to press ahead with the project. The world economic downturn was the primary motivator in this decision, costing Audi a fair degree of confidence. In fact, that would only return in the aftermath of the TT launch in 1997 - and by then, the gorgeous little Spyder was long dead and buried.

As might-have-beens go, the Spyder poses many questions - most potently, could Audi have become the powerhouse it is now years earlier? On the strength of the Spyder, it looks that the answer could well have been yes.