Following Clark's death at Hockenheim in early April 1968, Colin Chapman invited Spence back to Lotus as part of their Indianapolis 500 team, with the race in late May. Spence was due to race the revolutionary Lotus 56 gas turbine car. During practice at the Indianapolis Motor Speedway on Tuesday, 7 May, Spence, driving the #60 Lotus 56 turbocar (later qualified and driven by Joe Leonard), ran a lap of – fastest of the month and second-fastest in track history.