Here is a fun experiment you can all try!

Take a bike wheel, and slip something through or onto the axle so you can get a grip on both sides of it. You may be able to get enouch purchase by holding onto the quick release skewer.

Hold the wheel in your hands, as though your arms are the fork. Get the wheel spinning forward as fast as you can (don't get your hands caught in the spokes, or tag your face with the tire!)

Now that your arms are extended, and you have a wheel turning forward in your grasp, try countersteering, by holding on tight (again, like a fork), and then pushing forward with one hand. You should feel the wheel dive to the side, in the same direction you pushed. A push with the left hand will yield a lean to the left, and a push to the right will yield a lean to the right. Thats called gyroscopic precession! If the wheel is moving fast enough, you'll actually have to fight back pretty hard to keep it from slamming into your arm! There is a lot of leaning force available there.

There are more aspects of turning than just precession, including trail, and other geometric concepts, but the idea of a countersteer is to induce a controlled lean by forcing the gyroscope of your wheel to precess in the direction of the push. This lean then works with the trail of the bike to cause you to turn.

The great thing about countersteer is that because you are forcing the gyroscope to lean on its own instead of having to lean it by brute force, it lets you manipulate a gyroscope much more powerful than yourself. Thats why 96 pound people can race 540 pound motorcycles. They don't have the weight to lean the bike at 145mph, but they can countersteer, and let the bike lean itself!

Steering of a two wheeled device is facinating physics, that actually took a lot of development. If you want to ride a hi-wheeler 'pennyfarthing' bike, you actually have to unlearn most of your bike instincts, since it uses very different geometery and steering concepts.

peace,
sam