Late night thoughts: how did ancient chariots ever work at all? This is pre-rubber tires and shocks, and they're expected to operate at high speed across open plains undoubtedly filled with hidden rocks and pits
So, I know they were only ever used on flat terrain, its just that 99% of ancient battles took place on flat terrain *anyway*. The question is related to how flat terrain is still usually tricky to navigate for hard fixed-axle wheels
And they can't be limited to roads. For one, if battles took place on roads, there was only gonna be one narrow strip. You can't circle enemy infantry with one randomly placed road.
However it turns out that they did have limited suspension. Early models had very wide axels in order to limit the roll any given bump would deliver to the cab, and some later models had the cab hanging on a chain for shock absorption