No amount of padding can overcome G-forces. Only extreme and brutal training, like the one astronauts go through. The reason this happens is because they affect your inner organs and blood. From here:
Symptoms of encountering g’s include “graying out,” or passing out, due to blood flowing out of your brain and into your lower extremities.
So how does Tony not pass out from massive G's? How does he crash but remain fine inside the suit? Movie physics (derived from comic physics). If you instantly stop from going at 200km/h, you die, your body can't handle the acceleration change. This kind of physics just makes things more entertaining for us, viewers.
We can basically assume that as long as the suit remains, Tony isn't harmed.