According to Patently Apple, the U.S. Patent & Trademark Office has revealed an Apple patent application for a smart bike computer. Built around an iPod or iPhone type of device, the smart bike computer would work with remote sensors attached to the bike.
Like current bike computers, the Apple system would gather data on a bike's speed and distance traveled. But the Apple system would also monitor heart rate, provide GPS tracking and directions, provide gear selection, and be able to share the information in real time with a group of riders in a team.
As with all patents, filing a patent application isn't a guarantee that a product will ever be released. In this case, it's a very specialized market and not one Apple currently dabbles in. I think if this product ever sees the light of day, it will be as a design licensed to an existing bicycle manufacturer.