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Old 05-10-2007, 09:30 AM   #11
Buzglyd
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Default Re: Motorcycle Cornering Physics

Just say: "Son, I'm not going to lie to you.....Well gotta go!



And leave the room.
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Old 05-10-2007, 09:36 AM   #12
findangle
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Default Re: Motorcycle Cornering Physics

there is a good explination in the book mentioned at the top of the thread but its a little "math-ish".. there is a really easy to understand piece on wikipedia about this that basically boils down to this...



take a sharpened pencil and lay it flat on the table.. now roll it.. it rolls in a straight line.. now while still laying flat on the table, press the lead tip down against the table.. the pencil should now be at an angle with the eraser in the air.. now roll the pencil.. it turns... why? because there is less surface area around the pencil as you get closer to the tip.. the skinny part covers fewer miles then the fatter part given the same rotation speed..



bike tires work the same way.. there is less rubber around the tire on the edges.. so when you lean your bike to the left the tire rotation stays the same however the left edge doesnt cover as much distance as the right edge of the contact patch..



now think of a tank.. when the treads are moving at the same speed they cover the same distance.. when you slow the left tread down all the sudden the left tread covers less distance in the same amount of time. the result is the tank turns left.. if you were to keep the treads at the same speed but shorten the left tread you get the same result..



when your bike is standing up straight your contact patch is even.. so you go straight.. just like the pencil did when it was laying flat.. when you lean the bike over the part of the tire touching the ground (your contact patch) shifts to a part of the tire shaped more like the tip of the pencil.. and you turn..



this also explains why hitting the brakes mid turn makes your turn wider.. when you hit the brakes the bike wants to stand up.. and then your not on your turning part of the tire.. below 20-25 mph the lateral traction of your front tire forces the bike to turn with the handle bars instead of with the lean which is why counter-steering doesnt work at those speeds..
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Old 05-10-2007, 09:49 AM   #13
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Default Re: Motorcycle Cornering Physics

obviously a tire is round.. however if you turn it 90 degrees (so your looking at the tire as if you were standing in front of the bike) the tire is shaped more like a football with the tips cut off..



if you lean a football over and roll it what happens?



the football may be the best way to demonstrate the physics..



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Old 05-10-2007, 09:51 AM   #14
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Default Re: Motorcycle Cornering Physics

"below 20-25 mph the lateral traction of your front tire forces the bike to turn with the handle bars instead of with the lean which is why counter-steering doesnt work at those speeds.. "



Actually, the speed is lower than that - more like a slow walk.



Even bicycles countersteer: If you've ever ridden long-enough "no hands" on a bicycle, eventually you learn to corner that way as well. I observed the countersteering behaviour doing-so on my 12-speed as a child; only I didn't know what the bike was doing at that time.



I've tried this as an adult (one of The Wife's attempts to get us back in shape) and discovered (unfortunately) that "knobby" tyres are not exactly conducive to hands-free cycling...........

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Old 05-10-2007, 10:13 AM   #15
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Default Re: Motorcycle Cornering Physics

The little booger asked me while we were riding! He's finally gotten on the bike after years of refusing. Here's a kicker: he would NOT ride the HD. Got the Concours, now he wants to go all the time! The HD isn't that loud...maybe all those Japanese cartoons on Cartoon Network are subliminaly programming him?
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Old 05-10-2007, 10:24 AM   #16
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Default Re: Motorcycle Cornering Physics

It happens for basically the same reason you get pushed to the outside door of a car when it turns sharply. Newton's first law of motion says that an object in motion wants to stay in motion, in the same direction that it was traveling. Call it momentum. The reason your body moves to the outside door is because it doesn't want to turn, it wants to go straight. A bike operates under the same principles, but in a much more extreme version. If you tried to turn the bike by keeping it upright, its center of gravity (usually right under your hips) wants to go straight. if you can somehow move that center of gravity so that the bike wants to fall to one side, the two forces (momentum & gravity) act together to give you a general trajectory through the corner. There are way more things to take into account, like the interaction between the tire and the road, but the basic principle is as I laid it out.
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Old 05-10-2007, 10:25 AM   #17
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Default Re: Motorcycle Cornering Physics

I will tell you why..



to have something to relate to.. when you are driving in a car and you feel the sideways forces .. G forces .. that is the force created by changing the direction you are going. you know Newton's law.. an object will keep going till something changes it.. well same in a curve. you will go in a straight line till something moves you. well in a car it is being forced on a deflected angle by the front tires turning. this creates an acceration on your body too as a result.. .. ok so now jump to a motorcycle.. you still have to move your body and the motorcycle at a deflected angle. but since you are balanced you need the motorcycle and rider to 'fall' in that direction.. like when you balance a stick and you want to move it to the left.. you have to let it fall to the left .. same on a motorcycle you want to turn to the left.. so you need the motorcyle to lean to the left to stay balanced. the countersteering and all that jazz is just a way to implement the lean, and to create the curve that will create the centripetal forces that will keep you from falling when you are leaning in.



did that make sense?.. in simpler terms.. you fall inwards to counter act the forces of the turn that would normally throw you to the outside of the turn. because your body and motorcyle would want to keep going straight.
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Old 05-10-2007, 10:27 AM   #18
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Default Re: Motorcycle Cornering Physics

oops.. the guy above just said the same thing.
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Old 05-10-2007, 10:30 AM   #19
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Default Re: Motorcycle Cornering Physics

I guess you lucked out that he didn't ask where babies come from, and how they are made. Maybe he already has a handle on that one.
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Old 05-10-2007, 10:42 AM   #20
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Default Re: Motorcycle Cornering Physics

sort of..



the bike doesnt lean because it's turning.. it turns because its leaning. it sounds like simple word play but there is a very important difference there.



it doesnt NEED to lean in order to turn but if you did not use the "lean" method to turn then the forces acting on the bike (as described by newtons first law mentioned in the post above you) would throw you from the bike..



there are several ways to turn a bike.. turn the bars.. lean it.. heck you could even just pick up the front end. however your suspension is what keeps you off the ground and it's only designed to handle forces acting in a certain direction relative to the bike. if the direction of that force changes you must adjust the bike's relation to those forces to keep you on your wheels. leaning is the best way to both turn the bike and compensate for those forces.
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