system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why do some trucks have a pair of wheels that's a bit off the ground?

what purpose does that serve? and I don't think it's necessarily because of the risk of tipping over, because some of these trucks are quite long, and the risk of tipping is very low.
gpt
They do touch the ground, once they are heavy enough, they need to be on the ground to relieve stress on the other axles.

They are then raised when going around corners/bends so that they don't drag.

They are like the raised axles on a transport truck.