Not a game, but an interesting gadget made by Entex in 1981. This is a computer that was meant to mounted on the handle bars of your bicycle so you could see how fast you were going, etc. It's incredibly advanced, especially considering the time it came out. It featured: Average Speed, Peak Speed, Present Speed, Destination Speed, Target Time, Target Distance, ETA, Distance Remaining, Odometer, Ghost Rider, Clock w/ Alarm, Rest/Go mode, Stopwatch and could even be programmed to use a Heart-rate Monitor or Pedal Cadence Monitor (these devices were sold seperately). It even has a little animation of 'fence posts' on the display to simulate forward motion. It was kind of large though (about the size of an 80's desk-top calculator), and it mounted to the bike on a ball-joint type bracket. Apparently a common problem with the device was that it kept tipping forward out of the bicyclists line of site under it's own weight...
Here's the display from Toy Fair 1981 with a huge mock-up of the dislpay: