Originally Posted by Geekybiker
Well, it would make it harder to steer as well as keep it upright. It really should be on the rear wheel.
Below is an explanation from the FAQ how it works and why it should be mounted on the front wheel. It is consistent with explanation I heard some time ago on why bike are stable. When you lean for one side, the gyroscopic affect on the front wheel causes the handle bar to turn to the same direction. Now, that you move in a circle in the direction that direction, the centrifugal force pulls you outward and stabilizes the bike.
Here is an article that deals with this issue. Look at the diagrams at the last page
Becuase of the high speed turning mass, the Gyrowheel causes the handlebar to turn at a large angle for a smaller lean angle. Kind of amplifying the correction loop.
WHY DOES GYROWHEEL REPLACE THE FRONT WHEEL OF A BIKE AND NOT THE BACK?
The quick answer to this question is that it is the effect of precession that stabilizes a bike at high speeds, not what people typically think of as a gyroscopic effect. The front wheel acts like a flywheel (a fast spinning, heavy disk). As the bike tips to the side, precession will cause a torque that turns the handle bars toward the direction of the fall. Turning into the fall is how a rider overcomes instability and straightens the bike. At high speeds, the front wheel is spinning very quickly and acts as a big gyroscope. When you start to fall over, it’s the instantaneous turning of the handlebars that rights the bike.
Therefore, a flywheel on the back wheel would have no effect on turning the handle bars, and therefore almost no effect of stabilizing the bike in the way a gyroscope would (what most people think is the effect of Gyrowheel).
However, the precession force is strong enough to turn the handle bars and re-right the tipping bike ("TURN INTO THE FALL!" Is what one should be telling a person learning to ride). Gyrowheel simply amplifies the natural stability that is achieved when riding a bike at high speed (because at higher speed, the front wheel is like a big gyroscope).
The design of a bike is very sensitive to the alignment of the fork (how far over the wheel it hangs) because that affects how “quick” the turning effect is.