Ok, Line Rider isn't a bike game, and has nothing to do with bikes, but it's dang fun, incredibly addicting and amazingly simple. The closest thing it has to biking is the realistic physics in the jumps. You simply draw lines for your "line rider" to ride, and then if you want, draw a world around those lines. There is no limit to the size of the space (to my knowledge), and everything works off of gravity (although there are some "accelerator" lines I haven't played with yet).
I came across line rider while staying at my Uncle's house. My younger cousin Nolan showed me on his computer a couple days ago while I was heading to Oregon. Last night as I got to my hotel I spent about 2 hours putting together the following video. The best part was, the entire process was fine. Sure I can't do anything close to what I've seen some people do online, but me and my kids had fun just messing around and seeing how big we could make the jumps, whether or not we could get the little guy to land after a flip and creating our own unique track (line).
My only issue with line rider is that I wish I didn't have to draw with my laptop mousepad. I really need one of those tablets that desktop artists use. It would be much easier.
View the Line Rider Video | Make Your Own Line Rider Track