I'm 5'8" and size 26 and slowly going down (yea!) and carry mine in my torso. I haven't tried Rip Ride Rocket, but I fit on everything save Gringott's (my husband who's 5'6" and 165 couldn't do it either, it was too painful of a seat) and Forbidden Journey- but FB was weird.
Now, Warning- this SHOULD NOT HAPPEN TO ANYONE ELSE. IT was a complete FUBAR situation.
I knew I might not fit as I carry my weight high. I watched as guys more barrel chested and defined heavier than I tested chairs and were cleared. I cleared both the outside and inside queue test seats with no problem, but when I got on the platform I couldn't get the harness down in time (it STUCK) let alone pushed down, and the attendant immediately directed me to the side. I was told I didn't fit.
When I tried to explain what had happened, they called a lead. Who said I couldn't fit but I could ride any other ride, just give her name. Husband then started asking about the test chairs, and she got flustered. My anxiety sparked, as we were just off the side where EVERYONE was exiting. So I was ready to leave- where's the elevator as my husband can't take stairs.
Then it's oh the elevator is broken, you have to take the stairs. THAT got my attention out of my anxiety as I explained to her her couldn't take the stairs, he asked at the beginning of this if there were stairs and was told there was an elevator, so how are you getting him down? Their solution? Shouldering back through the Hogwarts queue against the people.
By the time we hit the end and were outside (swimming through the gift shop during the Harry Potter Weekend- go us), I was in tears from the anxiety. Husband went to Guest Services to explain what had happened exactly, after checking with the cast members at the front to see if they knew the elevator was out. They didn't.
Oh, and the guys who I saw testing earlier? They rode without a problem. I know they're bigger in dimension and size than I am because they were my brother's height (6'6") and at least his weight (335+).