Motorcycles are an interesting study in physics. To people who’ve never been on a bike, it’s a riddle how “these things” remain upright. I’ve been asked that question at stoplights in two countries, and the answer has always been the same: It’s the gyroscopic effect.
A spinning wheel provides stability about its axis, preserving orientation and position of an object in motion. A child’s spinning top stays upright as long as it keeps spinning. When it stops, it falls over. A motorcycle will, too.
Also, the stability imparted by the gyroscope effect is how motorcyclists make turns without falling down. It is, in fact, impossible to round a turn on a motorcycle without leaning.
Things get critical when the road is wet, covered with sand and gravel, or slippery for some other reason. When a cycle is leaning, a great amount of weight and acceleration force are acting on the rear wheel.
If that force is suddenly taken away, by an oil puddle for instance, the wheel slips in the direction opposite the turn (say, to the right in a left curve) and machine and rider go down. Experienced car drivers know to leave plenty of safety space behind a motorcycle, particularly on curving roads.
If a rider has to use the brakes while leaning through a turn, things can get really critical in a hurry.
The curves themselves seem weird at first sight, too. When you look at a race track, every turn is banked inward. The road surface in a right turn leans toward the right. A left turn leans left.
This helps round the turn at speed. But Georgia mountain roads do the opposite. Many novice motorcyclists learn this surprise fact by making a scary last-moment speed and steering correction.
There’s a good reason to bank regular highways against the turn. It helps spread and divert the rainwater. An inward-leaning turn has the shape of a funnel. In heavy rain, water will accumulate in the center and form a small river, rushing through the road curve. This would be a supreme hydroplaning hazard. Sloped against the turn, streams of water spread out and build up only to a low height.
In any case, because of the physics of motorcycling, it’s good practice to leave plenty of sideways and rear safety space for bikes on the highway.