Despite the death of Jim Clark, Lotus won both titles in 1968 with Graham Hill, but Stewart was a serious contender, winning several Grands Prix in the Tyrrell-run Matra MS10. Stewart's winning drive during the rain and fog of the 1968 German Grand Prix at the Nürburgring, where he won by a margin of four minutes, is considered as one of the finest ever, even though his rain tires were probably better than those of the competition. The car's most innovative feature was the use of aviation-inspired structural fuel tanks. These allowed the chassis to be around 15 kg lighter, while still being stronger than its competitors. The FIA considered the technology to be unsafe and decided to ban it for 1970, insisting on rubber bag-tanks (Which meant the effective end of spaceframe chassis in F1). Safety became a major issue in Formula One.