Be sure to check out the many other bike exergame setups profiled previously here on the ExerGame Lab blog.
Peddling at a certain rate holds down the A button to accelerate, left and right are buttons on the handlebars and there is a red button in the middle of the handlebars for using special items.
An Exercise Bike is the Controller for this Mario Kart Mod: 'via Blog this'
Check out his other mod using the same bike playing a Unity game designed by his buddy.
As part of an internal game jam here at the office I modified my SMKCycle (an exercise bike I retrofitted using Arduino to play Super Mario Kart on my SNES) to interface with unity and a colleague, Mike McGraw, made a 3-D game designed around the bike.
The game itself puts the rider in the position of defending the town/himself from rampaging alien oranges (The game jam had specific themes). There are 2 modes the bike can be in, a travel mode where peddling moves you forward at a relative speed and the left/right buttons turn left and right. Once you are in a position to fire on the vile citrus you can press the center button and switch to gun mode. In gun mode the tank stops and begins shooting (the rate of fire is commensurate to the speed at which you peddle) and left/right again turns left and right. At any time you can press the center button to swap between the different modes.