one of my companions was a very big guy. Not sure how big, but I am 6'5 and he was atleast as tall as me and huge (400 pounds or so I'd guess). Anyway, he had been in a car his whole mission, but the mission president decided that putting him on a bike would help his weight. I'll never forget trying to teach him how to ride a bike. First his helmet looked ridiculously small on his head. He managed to get going even though the bike looked like it would collapse, but the second he began to turn, his center of gravity would shift and the bike would just collapse on its side sending him straight down. We spent a whole day trying to teach him, we failed and he got a car again. It was a very memorable day though.