system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do 20 speed transmisions work? What vehicles use a 20 speed?
gpt
Think of it like a 4-speed transmission hooked to a 5-speed one in series.  The 4-speed gives coarse control and the 5-speed fine tunes between the coarse steps.

I can't imagine anything but a long-haul trick using something like this.  There are a lot of parts, and that costs money.  The precision adjustment would never pay for the parts.  In lighter cars, they use continuously variable transmissions for this sort of thing, so it would have to be a high-torque application.