Chains are transmissions of choice for many compact, ultralight wheel drives. For example, over a billion chain-driven bicycles operate on earth. However, chain drives don't yet operate on the moon.
Lunar-specific advantages of chains include location of drive motors away from wheel hubs and driving multiple wheels from fewer actuators.
Because the application is innovative, it requires extensive testing. A successful vacuum test simulated 40 kilometers of lunar driving in a hundred hours.

From AstroboticBlogPhotos