The Curiosity rover has six wheels. Its six-wheeled rocker-bogie suspension lets the car-sized vehicle cross uneven Martian terrain while keeping its instruments relatively stable.
Curiosity's wheels are made from lightweight aluminum and include cleats that provide traction on loose soil and rocks. The suspension allows the rover to climb over obstacles roughly as high as a wheel's diameter. Each wheel can be driven independently, and the front and rear wheels can steer, helping Curiosity turn and maneuver around hazards.
The wheels are not merely for transportation. Engineers use their patterns and wear to study how the rover interacts with the ground, while cameras inspect them for damage. Mars's sharp rocks have caused punctures and tears over years of driving, so mission planners choose routes carefully and sometimes drive backward to reduce stress.
Perseverance also has six wheels because it shares much of Curiosity's successful mobility design. The smaller Sojourner, Spirit, and Opportunity rovers likewise used six-wheel layouts, although their sizes and suspension systems differed.