The Honda PCX / Forza / ADV150 / SH Forums

Counter steering is another normal aspect of motorcycle steering dynamics that may seem confusing. Pushing the left bar end leans the bike to the left and makes you corner to the left. The opposite of a car or a quad runner.
.
http://www.renj.com/content/MotorcycleS ... eering.pdf
.

you you says "Fart before you start."

I'll paste another post I wrote at CBR250.net so you don't have to read through it over there.
.
Most of my commute is 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 most people haven't personally ever noticed it.
.
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.
.
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.
.
To answer your questions:
Motorcycle dynamics of turning and balance are very complicated.
.
http://en.wikipedia.org/wiki/Bicycle_an ... e_dynamics
.

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,
.
http://en.wikipedia.org/wiki/Precession
.
and the tire steering out to the right from under the cg on the roll axis which stayed where it was.
.
http://en.wikipedia.org/wiki/Camber_thrust
.
http://en.wikipedia.org/wiki/Cornering_force
.
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.
.
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.
.
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.

Mel46 wrote:Geek77, where are you located? I have never seen that bridge so i am curious about it.

That's the Vasco Da Gama Bridge in Lisbon, Portugal.

I live on the other side of the river.

http://www.golisbon.com/sight-seeing/va ... ridge.html

About the bike "knowing" how much to lean...

Are you guys trying to say that the bike would not fall, if we launched WITHOUT a rider and blew strong wind at it from one side ??? It would correct itself and keep going straight?

Please be reasonable.

I believe it.

A rider's unconscious balance and course guidance is needed occasionally to keep the bike upright and on course but the fact is that trail makes the bike stand itself up when it is leaned over. And trail makes the bike lean into a side wind with no rider input. As long as there are no stiff arms restricting the handlebars.

Perfect example of a bike riding away and leaving it's rider behind.
.

A racing motorcycle (one of the most unstable types of bikes).
.

.

It would be fun to take a motorcycle out to the salt flats and lock the throttle on 30 mph before turning it loose. It would undoubtedly drive itself around all day until it ran out of gas. Even in the wind.
.

.
.

This is along the lines of bikes want to go in straight lines when reaching speed, and not much speed is needed - hence why at speed you should lean into a curve not out (as some beginners will try when they panic) as there is already force trying to pull the bike upright and leaning away from the curve can actually unbalance the bike and topple it - gravity pulls the bike down, centrifugal force force pulls it upright - adding more to the outward force will at some point overcome gravity and you will topple outwards on a turn.
Counter-steering seems insane but when people try it it works so well above say 15mph http://en.wikipedia.org/wiki/Bicycle_an ... e_dynamics

It gets super windy here in Cape Town. In the last 10 working days, I've had to be a cager 4 of those days, due to the excessive wind. The worst was last Tuesday, and I heard via the grape vine, that a scooter got swept under a truck. I'm glad I drove that day.

Maybe we are not talking about the same kind of wind. Racetracks are isolated from strong wind on purpose.
My BMW moves laterally a little on that bridge, when the wind is strong.
There are electronic speed signs, which limit the speed to 90km/h (56mph) when the wind rises.
That's for cars. Imagine how a PCX handles in that wind. It's not something that could be corrected by the bike itself.

Windy?

If the winds are strong enough, they will blow any vehicle off the road. The best defense on a bike is to crouch forward so that you reduce the side area and lower the side center of pressure so the wind has less leverage at the top to push you over, and so that your upper body is anchored to the seat through your core so that you are not being blown over to lean and corner WITH the wind. And to stay light on the bars so that the automatic steering geometry response of the bike leaning into the wind can start instantly and unimpeded where short wind gusts swing the bottom of the bike out from under you to lean into the wind while the wind screen stays straight on line where it was. Additional countersteering pressure movements on the inside handlebar can be applied to further lean into the wind once you consciously decide that you are being moved off course by a long and steady side wind.