Sun out, roof down. What can be better for a cruise to the coast than this mid-century Mercedes-Benz 300SL Roadster? The 140mph machine has always been regarded as the poor cousin to the 300SL Gullwing. Now it's climbing in value, and just one glance at the svelte, sumptuous lines tells you why.

This pristine white example had just two owners when it was sold by RM Sotheby's two years ago for a then near-record £895,000. The 300SL Roadster was an as-new car, after a five-year restoration, and the price reflected that.

Bonhams sold a 1955 example at Goodwood last year for £651,100. There's still a price differential to a Gullwing - expect to pay £750,000 or more at auction - but it's narrowing as collectors realise the open car has real virtues of its own.

Based on the W194 racer, the 300SL project was suggested to Mercedes by the legendary American dealer Max Hoffman, whose ideas also influenced Porsche.

The Gullwing naturally grabbed the headlines when launched in 1954. The Roadster may just be the better car. Not only is it lighter but, because it inherited the tubular chassis necessary to support the Gullwing's doors, it's free of the scuttle shake of so many classic convertibles.

The Roadster is both luxuriously appointed and, drivers attest, a vigorous steer even by today's standards.