The SLS AMG was designed to be a modern 300SL Gullwing revival of the newly redesigned car. The car has a long bonnet, the passenger compartment is close to the rear axle and the rear of the car is short. The SLS AMG was developed from late 2006 in tandem with the Dodge Viper, with mules using Viper body panels over an aluminum chassis developed by Dodge SRT. The SLS AMG has also adapted the feature of wing doors that will swing open upwards on gas struts, not in a mix of upwards and forward like the SLR. The doors must be closed manually as AMG engineers decided against auto-closing systems because the systems would have added 90 pounds (41 kg) to the car. In case of a roll-over, the doors can be fully detached to allow the occupants to leave the vehicle.