re: heavy crosswinds

[Jim Huber <jhuber@xxxxxxxxxxx>]

>  From: Eric Sheley <eric@xxxxxxxxxx>, on 05/01/2000 09:58:
>  At 12:21 AM 5/1/00 -0700, don draper wrote:
>  >  The amount of effort required to correct for a crosswind is DIRECTLY
>  >proportional to the height of the CG above the roll center of the
>  >bike.
>  
>  Huh ? We weren't talking about the amount of effort required.
>  
>  The original question was not why it was required to lean in, but rather 
>  why in addition to leaning into the force there was also a certain amount 
>  of force that was required, directly opposite to the lean angle (in this 
>  case in the direction of the wind).
>  
>  Let me see if I can break it down a little simpler. I will forgo the vector 
>  mechanics discussions as I don't think that will make the scenario any 
>  clearer.
>  
>  These are some broad generalizations:
>  
>  1 - A bike travelling in a straight line will continue to do so unless some 
>  external force is applied (wind, input from the bars, throttle etc)
>  
>  2 - A bike travelling at a lean angle will travel in the direction of that 
>  lean (again very basic - we are not concerned with cg here)
>  
>  3 - If the lean angle is increased the radius of the turn will be decreased
>  
>  Of course in addition to the angle, the radius can be changed by tire size, 
>  tire profile, wheelbase etc.... we are not concerned with these factors
here.
>  
>  So we now have our bike travelling in a straight line. We now add a force W 
>  (wind) from the right, perpendicular to the direction of travel (things get 
>  really fun when the angle is <> 90). So in order to compensate for a 
>  quickly shifting motorcycle the rider begins to "lean into" our force W.
>  
>  Now - abruptly remove force W. What does the bike do ? It immediately 
>  begins to turn to the right. Now add the force W again. That same tendency 
>  to turn is still present - only now, force W is acting against it. However, 
>  if the combination of the lean angle and the profile of the tire at the 
>  contact point are such that a turn in the direction of travel is still 
>  being caused (even at a minute level), some force must be introduced into 
>  the equation to compensate (to cancel out this tendency to turn). In this 
>  case a constant pressure to the left would be required - which is why even 
>  though leaned to the right, Patti had to exert a constant pressure on her 
>  left bar to maintain straight travel.
>  
>  There - clear as ...... mud ?
>  
>  Respectively submitted
>  
>  - Eric

	Yep, clear 'nuff. And I agree with you, too. Pilots call it
"cross-control". It's the same thing you do when landing a plane in a
crosswind: bank into the wind but use the rudder to counteract the actual turn.

	"Jedi Dawg"  Jim Huber
	Spring, Texas, USA
	'00 blue ST  "Rhiannon"

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