I went up in the arch years ago but I don't think the car size has changed (hopefully they have a website that can tell you car size/age.) The fact is, the cars that take you up to the top of the arch are VERY small (like, "let's you and I get into an industrial size washing machine together!" OK, maybe a little bigger) I got in line with a friend who is about 5'6" and average weight, and when the door opened for us to climb into the car, she took one look in, said "no way" and left. I'm a little shorter, and I successfully made the ride up. The good news is, it's a short ride. The bad news is, you ride with at least one other person, so if it's hot, you hope it's early in the day. Also, the windows up top inside the Arch are relatively small and very thick, possibly plexiglass rather than regular glass so the view is cloudy. Bottom line - glad I did it once, would not do it again. Other people's experiences may of course be more positive.
The last time I was in St Louis I loved the grassy area below the Arch itself. I took lots of pics laying back, looking up at the sky and the Arch. I really loved the city itself, including the fabulous Art Museum a short bus ride away. When I was there they had great street art, often involving rabbits.