system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do tires on a car have air in them? Why not have them made out of solid rubber?
gpt
Rubber compresses yes, but not as much as air. Very early cars had solid rubber tyres and the ride was very bumpy (albeit combined with very primative suspension).  Also the solid rubber tires would "bounce" like a rubber ball, not ideal.  Air inside tires however acts like a shock absorber... then once the tire has returned to its original shape, the air doesn't spring back the other way like solid rubber would.