I only had a short time in Bali and found the bike tour online. I stayed is Nusa Dua and was picked up on time no problem. I did look on the website to see how fit everyone was. I thought to myself if everyone looks like Lance Armstrong then I probably won't sign up. But like the others have already commented it is very enjoyable mostly downhill. A great way to see the country side. If you are nervous about traffic we were on the back roads most of the time. Anytime we were on a main road there was someone ahead to stop traffic for us to cross. There was also a driver behind the group as well for safety.
Mr. Bob, the tour guide, is a local guy who is great at giving insight to the village life. And at the end a delicious Balinese lunch is prepared by his wife is delicious. Honestly the best day I've had in a long time. You won't be disappointed.