Oh, and as a very rough rule of thumb, you can ride more in a special event than everyday (because of rest stops and food and all that). We "decided" in our group that it's about three times as far. SO... If you can do 12 or 15 comfortably, and not be worn out the next day, then go for the 40. If five or six is what you're happy with... stick with the ten. You don't want to be so miserable that it takes three weeks before you want to get back on a bike.