On August 6, 2012, at 05:17 UTC, NASA has successfully landed a Mini-Cooper-sized rover, Curiosity, on Aeolis Palus in Gale Crater on Mars. The 900-kg rover (899 kg, to be exact, which is 1,982 lbs) is equipped with six 50 cm (20 in) diameter wheels in a rocker-bogie suspension (see notes 1). For the first time in the history of space exploration, the suspension system also served as landing gear for the vehicle, unlike its smaller predecessors.
Curiosity “soft-landed” (wheels down) on the surface of Mars. But, even it’s called “soft-landing”, the touchdown speed was 0.6739m/s vertical and 0.044m/s horizontal, which could damage the wheels. Plus, while the rover is moving, the wheels should withstand the substantial damage through the rough Martian surface. That’s why the wheels of the Curiosity rover have been one of the biggest technical difficulties encountered on the mission (see notes 2).