A couple of next-generation S-Class prototypes undergoing long-distance stress-testing on the ring.

Here are the latest spy shots of the 2013 Mercedes-Benz S-Class doing some durability testing on the Nürburgring-Nordschleife.

Mercedes is now running a couple of prototypes on the circuit, stress-testing them by going round-and-round the track to see if there are any weaknesses to be found.

Petrol-engines expected to power the next-generation S-Class are the 306 PS (301 hp / 225 kW) 3.5-liter twin-turbo V6, the 435 PS (429 hp / 320 kW) 4.6-liter twin-turbo V8 and the V12 with 552 PS (544 hp / 406 kW). Diesels, of course, will also be part of the lineup. 

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