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The development of the Mercedes SLS AMG Roadster is well underway ahead of its public debut at the Frankfurt motor show this September.

Fitted with the same 571bhp engine as the coupe and weighing only slightly more, its 0-62mph time should still be around four seconds. Convertibles are usually much heavier, due to the extra stregthening needed under the chassis when the roof is removed. The SLS AMG was designed to work well as a convertible from the outset.

Unlike the Mercedes SL and the new Mercedes SLK we recently tested, which famously sport a folding hard top roof, the SLS AMG Roadster will feature a hydraulically operated soft top, which is lightweight and can open and close in 11 seconds at speeds up to 31mph.

The hood is designed to withstand maximum speeds of 197mph, whether up or down and all while allowing minimum noise intrusion or vibration into the cabin.

Its ability to withstand water has also been tested with spray hoses, overnight rain simulators, driving through fords and automatic car washes. Prototype hoods have also been raised and lowered more than 20,000 times each.

Engineering changes include a reinforcing crossmember behind the seats and a fixed rollover bar. The 250-watt Bang&Olufsen subwoofer fitted in the SLS AMG has been carefully repositioned as a result of changes in the rear of the cabin, and its acoustics tweaked to deliver the same clarity of sound.

More than 10,000km have been spent 'Accelerated endurance testing' at the gruelling Nurburgring Nordschleife and the same distance has also been driven in city traffic.

Going on sale in Autumn 2011, expect the Mercedes SLS AMG Roadster to cost around £180,000.

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