Quote:
Originally Posted by redyaris
How does the bike know how much to counter steer?
How does the bike know how hard the wind is pushing it?
At what point does the bike stop countersteering?
Motorcycles are not self correcting |
Well, we have obviously hit your nerve on this topic. I'm not sure why anyone would feel so adamant about this but any way. I am not a suspension designer but I can tell you this from riding 6,000 miles this year. Most of it on relatively straight divided highway at 65mph and often in side wind conditions. My motorcycle is very noticeably self correcting in side winds. I could demonstrate this to you "no handed" by laying on the tank and momentarily letting go. But you have to lay on the tank while riding to get the best effect which most people find self conscious or uncomfortable. Other riders suggest "riding with your knees" to take the weight and stiffness of your upper body off of the handle bars. This helps free up the steering but doesn't work quite as well. Maybe this is why you haven't personally ever noticed it.
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If your upper body is sitting high and free from the bike as most people do, it will spoil the effect that the steering geometry has to roll the motorcycle into the side wind. Cross winds pushing on the side area of the bike/ rider/ luggage that is above the center of gravity of the roll axis will cause the bike to lean over and actually turn off line the wrong way. Worse yet, blowing the rider's head and torso to one side of an upright, yet comfy riding position of a standard bike, pushes the rider out of position from over the balance line which has made the system lean and turn the wrong way. The next thing that probably happens is that the rider will try push their upper body back over the bike against the wind with their far side arm which applies a counter steering manuver to the handle bars. The wrong way. Which makes the bike lean the wrong way even further. All of this happens in a domino effect very quickly, blowing you off line. If you sit up.
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Super Sport bikes with their ultra low and narrow clip on handle bars place the rider in a better position to avoid all of this in the de facto riding postion they impart by lowering the rider's upper body, and so, the side wind center of pressure. And further, reducing the leverage that the side wind has to push the rider's upper body off the bike. My CBR250R offers the best of both worlds with high, wide bars for sitting up in traffic, and, perfect ergonomics to lay down on the tank to get out of the wind in order to let the suspension use it's trail to lean the bike into the wind.
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To answer your questions:
Motorcycle dynamics of turning and balance are very complicated.
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Bicycle and motorcycle dynamics - Wikipedia, the free encyclopedia
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Motorcycles have trail. The contact patch of the front tire is behind the steering axis. When the side wind pushes the whole bike to the right, the contact patch is stuck to the road behind the steering axis. The steering axis, which is in front of the patch, is free to move to the right more than the contact patch which is stuck to the road. The wheel has just torqued and steered to the right. Which causes a counter steering lean of the bike to the left through the combination of gyroscopic precession leaning the the wheel,
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Precession - Wikipedia, the free encyclopedia
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and the tire steering out to the right from under the cg on the roll axis which stayed where it was.
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Camber thrust - Wikipedia, the free encyclopedia
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Cornering force - Wikipedia, the free encyclopedia
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The motorcycle has just leaned to the left into the wind. Automatically. The same as if you had consciously pulled on the right handle bar to initiate a counter steering maneuver. If the center of pressure of the side area of the rider/motorcycle is below the cg of the roll axis, this would also tend to lean the bike into the wind. Or at least stop the distribution of the wind pressure from fighting the roll force of the counter steering trail if the wind pressure is at least neutral to the cg.
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Trail also tends to make the bike stand up from a lean. When the bike leans to the left, there is an increasing vector of gravitational force pulling on the left side of the bike. To the side of the steering axis. Which is again free to move more than the patch. Causing a counter steering torque to the left which makes the bike lean and steer it's tires back under the bike until it is upright again.
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The more the bike leans, the less area is presented to the side wind and, the more gravitational force is applied to the trail to make the bike stand up. Careful design has made a nice balance in the amount, and vertical distribution of the side area of the CBR250R, and the amount of trail, in order to balance the forces so the bike "knows how much to lean" into a side wind.