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Motorcycle steering

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skenn

skenn

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May 10, 2002
28
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.
 
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Try 2 experiments....on a straight, empty road. Try to steer by weight shift only..it doesn't work.
Click to expand...

Sorry, skenn...I must respectfully dissagree. I read your post and decided to try the weight shift as I felt your conclusions incorrect. As I determined on my 1948 Norton, I can very effectly steer the little beastie by shiftin my weight from side to side as long as speed is maintained with my hand off the throttle. I tried the finger push deal, but it only takes a VERY slight touch to make the Norton really take off...too spooky to continue on the canyon road I was on.

Rod
 
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Does it realy work, other than for a few yards ?. Could you actually negotiate a bend like that ?. I find that I just get a very brief wiggle('81 Duc Pantah), but as you say...pinky against the bars is plenty !. Maybe I should have said a WIDE, straight, empty road.
 
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I can ride my pushbike for miles by weight steering alone, including around curves. I'd be astonished if the dynamics of a motorbike are so different that weights teering doesn't work at all.

In fact if you think about it countersteering is effectively weight steering, it displaces the cg laterally.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
 
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I suppose it depends on how big your arse is!;-) nyuk,nyuk! Also, my bike is a bit closer in configuration to the 1930's than the 1980's...to say the least. It's still set up for road racing but has been equipped with lights... the street legal stuff from an ES-2. It once belonged to Bill Young, four times world champ back in the day.

Rod
 
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Weight steering does contribute. On the track/street, in addition to countersteering I'm also putting weight, through the pegs, to one side of the bike or the other depending on how I want the machine to respond. Add to that the amount or style in which I hang off, and there is a weight element. Not as great as countersteering, but there is an effect.

And your theory works on standard to sport-rake motos. Start heavily changing that tube angle (think choppers) and the experiment goes down the tubes.
 
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evelrod
I had an ES-2. Good handling machine, but not much go.
Pushing on the handle bars to upset the center of gravity is the best way to initiate a turn. Counter steering is then required to continue the turn.
 
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Can't remember who, but either Keith Code or Reg Pridmore affixed a second set of handlebars (i.e.dummy handlebars) to a motorcycle. These dummy bars were not attached to the steering stem. Then he would challlenge the "body steer disciples" to try to ride the bike. They couldn't. The implication is that body shifting will cause the rider to also move his arms and countersteer the bike, even though he may not be perceptible of his arm movements.
 
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I think I'd better keep quiet about my opinion of choppers !.

It would seem taht well balanced bikes would be largely imune to weight-shift alone. No offence intended to vintage machines. I CAN get my Duc to turn, but only with a series of nudges...just leaning out has almost no effect, as the CofG actually remains that same...over the contact line. You lean one way, the bike leans the other. Your weight shift causes an equal and opposite shift in the bike's.
 
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FJTOM.
My 48 is much modified, as I stated it belonged to a world champ in WA (Oz) and has a very much modded 500cc with an extra close ratio racing gearbox, International tanks, Brooklands exhaust, Int. forks and brakes, 19" and 21" wheels, etc. Still the "look" is pretty stock to the uniniated, non Norton fan.

skenn.
I live in an area of southwest Riverside Cnty. near the Ortega Hwy. I see a very large number of bikes on a daily basis and am somewhat surprised that there are so FEW choppers being ridden in the area. Perhaps only one in a hundred or so...and even then, they are not of the hugely extended fork variety. ??? Perhaps I watch too much telly?

Rod
 
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Like a magazine report years ago, comparing a Guzzi with a big honda..both handled like they were on rails....the difference was that the rails the Guzzi was on went round the bends...the honda's ones were dead straight, regardless :) .
I think Choppers are for long straight roads !.

S.
 
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Rod, I'd say you don't see them in most areas due to the cost. Honestly, when entry level custom choppers are running $40K, the average guy can't afford to ride one. And with all the custom work on those, I'd be afraid of paint chips and the like. Those are "ice cream cruisers". It's probably the reason I can't bring myself to put down the cash on a newer Duc or Aprilia.
 
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3Z.
I'm just a month away from 67 and I just don't have the desire to drag my knee in the corners any longer. I rather prefer to just cruise around on a nice vintage bike. I have so much invested in vintage racing (cars) that there just is not enough of me to go around or get back into bikes full time. I'm guessing that I've paid my dues. I still love to stop and talk/look at the gals on the custom bikes, though. ;-)

Rod
 
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I like the term "Ice cream cruisers"...someone on of our TV chatshows said... a Triumph(referring to the old Company..before the name was revived) is a motorcycle...a Harley is a fashion accessory. I wouldn't go QUITE that far, but I never had the desire to own a Harley.
I had wanted a Pantah since they were in production, and finally decided to buy one from England....when I brought it back to ireland, I found that there was on residing 4 miles from me that was open to offers !.

S.
 
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Skenn
I had a 78 Ducati GTS which I thought handled pretty good,
until I spent the summer riding my Norton out of a canyon in Colorado. When I went back to riding the Ducati I actually pulled over trying to figure out why it wouldn't turn..Flywheel effect was all it was.
I started noticing that all my bikes had a different flywheel effect from the Guzzi to the Norton and in between.

I know the newer Ducati's have less flywheel than my old GTS
but I can only attest to my 900 Monster..

Cheers

I don't know anything but the people that do.
 
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Shifting your weight will steer the bike (sportsbikes anyway). There's a fixed steering R6 that i've ridden to prove the point that you can ride.

You effectively tilt the bike, and apart from cog, you have different tire profiles front and rear so all this helps you turn.

I race, and apart from the knee dragging that happens 'cos yer do' shifting your weight is a hufgh part of the turn. Several tracks that I race on see me shifting my weight before the turn to make the turn sweeter. To enable me to do this & still travel forward in a straight line I have to tilt the bike and countersteer. belive me it's common place

Dansoarr
 
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OK, so I was wrong...weight shift can make it turn .. depending on the geometry :) .
 
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Dansoarr--was this the bike Keith Code built?
 
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I am no expert but I have Tony Foale's excellent book on motorcycle chassis design.

He clearly explains the physics of countersteering to initiate the turn.

Hanging off the bike like all good racers is explained simply as allowing a tighter radius turn with less bank angle (and more ground clearance and less lateral tyre load) on your bike.

I could go on all day quoting from Tony's work but have a look at the free articles on his website ( and read the one titled "Balancing Act" which sums it up....or order his book.
 
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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.
 
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