ok, you can GUESS a combination?
are you ********? why would you go for a combo. it's four digits, there's a finite number of combos for it, and if someone has enough time they'll be able to get it.

as far as losing keys: i've lost two and had one break on me... i just keep extras in my bag, and whenever i lose one it's not too big a deal since i use two locks at the same time. what are the odds if someone finds a key they'll be able to guess what bike it belongs to.