Friday, May 29, 2009

Countersteering - Leaning to Turn

As I explained in my previous entry, the biggest misunderstanding about how to steer a motorcycle is a result of how we first learn to ride two-wheeled very slow speeds.

The art of balancing a motorcycle or any two-wheeled vehicle involves steering so that the wheels stay under the bike. At low speeds, (on a bicycle, for example) the rider is constantly steering in the direction that the bicycle is leaning, to prevent the bike from falling over.

There's nothing WRONG with this...that's exactly what a rider should be doing. The problem is that the rider doesn't realize how the turn was initiated in the first place. They assume that because they are steering in the direction that the bike is turning that it's their steering motion that causes the bike to turn. This is a half-truth at best.

Now this usually isn't a problem for most bicycle riders. At bicycle speeds, most people learn subconsciously that to steer the bike, it has to be leaned over first to initiate the steering motion. But the rider not realizing this consciously comes back to bite them when they move to a faster vehicle, such as a motorcycle.

Steering a Car - The Stability of Two Wheel-Tracks

In the previous post, I talked a little bit about the difference between cars and bikes. Now I'm going to talk a little more about those differences, specifically how a car steers differently from a bike.

Cars and bikes are both affected by Newton's First Law of Motion - mass going in a straight line wants to keep going in a straight line. Turning is "unnatural" for anything and requires force.

When you turn the wheels of your car, it's the force of the tires tracking to one side that pulls the rest of the vehicle (and its passenger) through a turn. When you turn your car hard to the right, for example, as the wheels start to track to the right, you will feel the rest of the car wanting to keep going straight. This manifests itself as the body of the car rolling to the outside. You feel it in your body as well, as a hard right turn will have you pressed against your driver-side door. (or the center-console, for those who drive in left-laned countries)

Think about what would happen if you tried to turn sharply at speed in a top-heavy box truck or van. As the tires turn one way, the body of the vehicle could actually ROLL the other way, tilting to the outside of the turn and eventually capsizing. (I almost did this with mom's minivan when learning to drive)

This is why sporty cars are designed low to the ground with wide wheelbases. When a vehicle has two wheel-tracks, one opposes the tendency of the other to lean to the outside when turning. The inside two wheels can't tilt to the outside because the outside wheels are bracing them. The outside wheels cannot tilt because the inside wheels are weighing them down.

So the inside wheel-track and outside wheel-track actually cancel each other out and prevent the car from tilting over as the wheels move in the direction they're turned. The chassis, being connected to the wheels, is dragged through the turn by sheer cornering force. This act of the inside and outside tires fighting each other results in the pronounced howling you hear when a 4-wheeled vehicle negotiates a hard corner.

Steering a Motorcycle - The Consequences of One Wheel-Track

When you steer a motorcycle, the process is different. There is no opposing track of wheels to stabilize a motorcycle. That means that when the front wheel starts to turn in one direction, the rest of the bike wants to continue in a straight line. Now there's no second set of wheels to help prevent this tilting motion and drag the rest of the bike through the turn like the car.

This means that when the front wheel of a motorcycle is turned, the wheels actually steer out from under the motorcycle. The bottom half of the bike goes in the direction that the wheels were steered, while the top half of the bike tries to keep going straight. The result is that the motorcycle leans.

For example, if you're moving at a decent clip on a motorcycle and you turn your handlebars to the right, the tires will steer out from under you to the right. Gravity starts to pull the top half of your bike downward, now that your wheels are out from under you. The end result is that the motorcycle will lean to the left.

"The Bike is Fighting Me!"

When an untrained motorcyclist tries to turn at speed for the first time, he will often complain about the motorcycle "fighting" against his turning motion. This is because when the motorcycle is moving at speed, the untrained rider will try to initiate a turn by turning the bars in the direction he wants to go.

What happens when he does this is that the tires of the bike instantly steer out from under the rider in the direction that the bars were turned, causing the bike to make a sudden tilt in the opposite direction. This actually ends up steering the bike in that opposite direction...but more on that later. The typical rider usually gets scared as soon as he feels that unfamiliar tilt and immediately straightens the bars. The result is that he thinks that the machine is "fighting him" for control.

I first experienced this on a 90cc scooter that my uncle had bought to get around-town prior to purchasing his Harley-Davidson. I had taken it out for a spin not even having ridden a bicycle in several years. I was doing all-right until I drifted slightly wide and ended up headed for a parked car. I tried to steer quickly to the left, but the result was that the scooter leaned to the right and directed me even closer to a certain crash. (I managed to brake before I hit the parked car, but it scared me enough to where I knew I didn't know what I was doing!!)

The Simple Truth - Bikes Cannot Be Steered Like Cars

The bottom line is this: a motorcycle can't be steered like a car. Unless you want to put training wheels on your motorcycle, or you have both feet on the ground and are walking the bike around the garage, a motorcycle doesn't have the static balance a car does and cannot be turned by steering in the direction that you want to go.

The result of steering a bike in the direction you want to go is that the bike will lean in the opposite direction as your wheels steer out from under you.

This is a good thing for two reasons. The first is that this steering of the wheels independent of the mass of the bike is what allows your bike to stabilize itself at speed. Again, the previous article goes over the physics of the front wheel and how the front wheel keeps your bike upright by constantly steering in the direction the bike is leaned.

The second reason that this is a good thing is that by steering the wheels out from under you and back, you can use the handlebars to control the lean of the motorcycle.

How to REALLY Steer a Motorcycle

Now that the first two "Countersteering" articles have laid the groundwork for understanding how a motorcycle steers, the next "Countersteering" article can finally explain how to turn a motorcycle, hopefully in a way that the average rider can understand.

The short explanation, though, can be summed up like this:

1 - Motorcycles cannot be steered like cars...they will lean in the opposite direction.
2 - Given #1, motorcycle handlebars can't steer the motorcycle, only control its lean.
3 - Given #1 and #2, the only way to steer a motorcycle is by controlling its lean.

More later.

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