Motorcycle steering

[skenn]

I'm sure this has been discussed before
It is all down to the effective combined forces of gravity, and centrifugal force caused by turning, and it's position relative to the tyre contact points.
Try 2 experiments....on a straight, empty road. Try to steer by weight shift only..it doesn't work.
Now, with your hands off the bars, apply a little forward PRESSURE on one side, then allow thebars to push your finger back. As long as you continue to apply pressure, the turn continues to increase. What you are actually doing, is keeping the CofG to one side of the contact line...keeping the bike slightly off equilibrium. When you release the pressure, the turn remains, or gradually reduces.
The initial pressure moves the front wheel slightly, thereby moving the contact line out from under the GofG. The fork rake, then turns the steering into the turn, attempting to get the force vector to act through the contact line.

 

[Blackjacks]

Evelrod,

You live in OZ? Well you probably don't see that many choppers because of the reggo rules you have over there...

Friend of mine builds them in Sydney and from what he's told me, getting them through the engineers inspection is a bit of a mightmare.

 

[evelrod]

No Blackjacks, I live in Socal, southwest Riverside County. My 48 Norton came from WA, Oz. It was shipped to the U.S. a number of years ago in a 'semi' restored condition. With a few more bucks and a lot of TLC it runs and rides pretty much as you would expect of a 1948 racing motorcycle, often scares the heck out of me watching my 125 lb. son carve his way up the canyon on it. I really appreciate the "old timers", like Bill Young that, back in 1949/50 managed to make my bike the fastest/quickest 500cc bike in the world! Not me!!! I just "put around" and show it off.

Rod

 

[oab]

Quote Skenn( OK, so I was wrong...weight shift can make it turn .. depending on the (geometry)?)Quote.

Depending on speed.

Quote Skenn(Hanging off can't affect lateral load. That is purely mass and angular velocity. It only affects how far up the side of the tyre the load acts.)

Yes that would be right, if the steering axis was vertical, but it is laid back at an angle of 22 to 30 degrees from the vertical. As the bars are turned, two things happen, first the frame of the bike will move to the same side that the wheel was turned to. Second the weight bearing axle will drop closer to the ground, forcing the wheel to turn.

This is what allows Greg to ride his bike 'no hands', by moving his weight to one side, causes the frame to lean and the axle height to drop, turning the wheel in the same direction. You can do this by just holding the seat and leaning the frame side to side.

This happens when stationary, or at the low speed that Greg can pedal. As the speed rises and the wheel develops Gyroscopic force, the wheel starts to resist turning, so leaning the bike has less effect. In fact the wheel now resists turning. Turning the handle bars now will cause the Gyroscopic force to lean the frame in the opposite direction. So to turn the bike to the right, we now have to push the bars to the left, to get the bike to lean to the right, then allow the steering axis to bring the wheel back to track the corner.

Thundair

Compares a 78 GTS Ducati to a Norton. This is opposite ends of the steering axis angle. The Duck has a 30* head angle, that increases the Gyroscopic effect and the high speed stability, while decreasing its fast steering ability. The Norton has a 26* head angle, that allows it to turn fast, but is a bit twitchey at high speed.

Rod.

I had two Ducks, a 76 750 SS and a 72 450 single. The 750 with a 30* head angle is rock steady at high speed, but changing lanes is by appointment only. The 'Silver Shotgun'with a 24* head angle, could turn fast enough to drag your elbows, but anthing over 160kph was dicey.

Harvey.

 

[thundair]

oab
There are a lot of things that make them different IE tire size, trail, head angle, length and weight... but my focus was on flywheel effect..That was made clear to me when I shortened the swing arm and change the head angle on my 78 Darma. It was quicker through the tight stuff but still had a lot of flywheel effect

Cheers

I don't know anything but the people that do.