Author Topic: Sport-lowrider bike (Read 979 times)

easymo · « **Reply #30 on:** October 06, 2002, 04:15:54 AM »

What part of this did you not understand?

Now, why does this make a difference in corner negotiation. We must understand that the wheels of a motorcycle act as a gyroscope, and that this gyroscopic effect is increases in proportion to speed. One property of a gyroscope that applies here is the reaction called precession. When a gyroscope is acted upon by an outside force (in this case, gravity, when the bike is leaned over) it will react, or precess by causing an opposing force acting at 90 degrees to the applied force. Since gravity acts downward through the center of mass of the bike, the opposing force from the gyroscopic effect of the wheels will act at 90 degrees to this, which in a flat corner will be parallel to the ground, opposite to the lean of the motorcycle.

This reaction has its pros and cons. The gyroscopic effect is what keeps the bike from falling over in a turn ( in spite of gravity). It is not momentum that causes this! However, this effect also means that as you try to lean your bike in a fast sweeper, or try to accelerate through a curve, there is a force acting to straighten the bike up, which may cause you to drift wide, and then perhaps cause the worst!

When you shift your weight into a corner, you effectively move the center of mass of the entire rider / bike package further from the tire (contact patch). The effect is that resultant force pulling the bike down into the turn is greater. (This is the same principle as using the length a lever to increase resultant force)

SaburoS · « **Reply #31 on:** October 06, 2002, 04:39:35 AM »

Quote

Originally posted by easymo

BTW. The lack of knowledge, in this thread, of something as basic as cornering, is what is funny.

easymo, from your vast motorcycling knowledge, please comment to the attached. So you're saying that those riders attained their lean angle on their bikes by shifting their body weight over their bike and not by steering input? Please give us a running description of what they did to enter the turn to get that angle?

BTW I don't believe anyone here that rides bikes disputes that the bike has to lean for the turn, just how to get the bike to lean. Re-read my posts above.

SaburoS · « **Reply #32 on:** October 06, 2002, 04:59:10 AM »

Quote

Originally posted by easymo
What part of this did you not understand?

Now, why does this make a difference in corner negotiation. We must understand that the wheels of a motorcycle act as a gyroscope, and that this gyroscopic effect is increases in proportion to speed. One property of a gyroscope that applies here is the reaction called precession. When a gyroscope is acted upon by an outside force (in this case, gravity, when the bike is leaned over) it will react, or precess by causing an opposing force acting at 90 degrees to the applied force. Since gravity acts downward through the center of mass of the bike, the opposing force from the gyroscopic effect of the wheels will act at 90 degrees to this, which in a flat corner will be parallel to the ground, opposite to the lean of the motorcycle.

This reaction has its pros and cons. The gyroscopic effect is what keeps the bike from falling over in a turn ( in spite of gravity). It is not momentum that causes this! However, this effect also means that as you try to lean your bike in a fast sweeper, or try to accelerate through a curve, there is a force acting to straighten the bike up, which may cause you to drift wide, and then perhaps cause the worst!

When you shift your weight into a corner, you effectively move the center of mass of the entire rider / bike package further from the tire (contact patch). The effect is that resultant force pulling the bike down into the turn is greater. (This is the same principle as using the length a lever to increase resultant force)

LOL! Try riding in a straight line with your bike leaned over. You'll fall over.
It is the fight between the forces of gravity and centrifugal force that keeps the bike in check in a turn. Too much centrifugal force in a turn and you'll highside it (provided the tires keep their grip) and go flying off your bike. Lowslide it if your tires lose their traction. As long as the net vector force (gravity + Centrifugal) drives the bike through its tire's contact patch with the road's surface, you'll keep traction and the turn rate.
(I sure wish waaay back in school I paid more attention in my English class. Seems some are having trouble understanding what I'm trying to type.

)
BTW, how do you make emergency avoidance maneuvers? Shifting your weight on your bike only? Can we say accident?

easymo · « **Reply #33 on:** October 06, 2002, 05:02:15 AM »

I don't see any point. You have decided you have it all figured out.

I will tell you this. I once won a hundred bucks from a guy by doing what you see in the pic. Holding on to nothing but the gas tank with both hands. He has his weight shifted forward, collapsing the forks ever so slightly and changing the steering geometry. His knee sticking out is causing a lot of wind resistance. this allows him to cause additional opposing force by "pulling'' the bike into the turn. You can do the same thing pulling on the tank. I could go on, but I think i am wasting my time.

SaburoS · « **Reply #34 on:** October 06, 2002, 05:28:23 AM »

Quote

Originally posted by senna
Easymo is right about the rake stuff. The steeper the rake, allows for faster lean and angle stuff. Countersteering is a phenomena (SP) of "thrust camber" and the gyroscope effect is what pulls the bike or leans it the opposite of the direction of force of the object to the direction of the turn (bike and riders head should lean to outside of turn if not for counterstearing). Gyro causes wheel and road angle close from 90 degrees like what was said above. IMHO, counterstearing is required because a motorcycles tires behave differently than a cars tires. Cars generate slip angles with higher performance tires having steeper slope slip angles drastically droping off. Motorcycle tires instantly generate negative slip angles sort of reverse of an automobiles tire. On a motorcycle, after 15-20 miles per hour, you turn the bike (of course) by countersteering. Reason is is that at that speed, the tire actually goes into an instant loss of traction (bst way to describe it in relation to how car tires work). In a car, if you loose traction at rear, you would countersteer. On a bike this sort of happens automatically (not noticable) thus you must preemptively countersteer to turn in the opposite direction. This concept is better understood if you look at it from a tires slip angle graph (which is how I figured it out).

Hmm my front tire doesn't normally lose traction in my countersteer input for a change of direction (nor would I want it to lose traction). What I see happening is that the front tire steers out a bit before turning it back. The bike's center of gravity has now shifted from its base of support (tire's contact patch) forcing the lean of rider and bike in opposite direction of the countersteer (via lever action pivoting around the center of gravity.). The accelleration (change in direction, read turn), helps create centrifugal force keeping the lean in check. Too much lean in a turn and you'll slide it out from under you. Too little and you'll highside it.

DblTrubl · « **Reply #35 on:** October 06, 2002, 07:54:03 AM »

Interesting discussion. Last year I took the MSF advanced rider course. I was able to find some of the reference material they gave us. I think it might clarify this issue a bit. I'll try to attach it...hope I sized it right. Here goes nothin.

DblTrubl · « **Reply #36 on:** October 06, 2002, 07:55:22 AM »

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DblTrubl · « **Reply #37 on:** October 06, 2002, 07:56:51 AM »

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DblTrubl · « **Reply #38 on:** October 06, 2002, 07:58:16 AM »

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DblTrubl · « **Reply #39 on:** October 06, 2002, 07:59:29 AM »

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DblTrubl · « **Reply #40 on:** October 06, 2002, 08:00:30 AM »

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DblTrubl · « **Reply #41 on:** October 06, 2002, 08:01:21 AM »

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DblTrubl · « **Reply #42 on:** October 06, 2002, 08:03:13 AM »

Last one. Sorry in advance if I killed anyones load times. I made em as small as I could while still keeping em readable. S!

Holden McGroin · « **Reply #43 on:** October 06, 2002, 12:14:24 PM »

One of Newtons laws of motion has to do with the observations of effects of Inertia:

Things at rest tend to stay at rest unless acted upon by an outside force.

Things at a constant motion, (non - accelerating) tend to stay at that constant motion unless acted upon by an outside force.

The only place a motorcycle or bicycle has that acts with the outside world is the tire contact patch. In order to upset the balance of the cycle, the only choice is to steer out from underneath your center of gravity. (unless you push against a car pacing beside you)

When you lean into a corner without countersteer, the geometry of the front forks causes the front wheel to turn, and that in effect causes the countersteer you don't think you are doing. This is how you can ride "hands off".

As for a low center of gravity, this is good in a car, because it keeps the car from rolling or tumbling before the tires lose traction. It is not necessarily an advantage in a vehicle that needs to be balanced. Ever try to balance an ax with the head down? It is a lot more difficult than with the head up...

SaburoS · « **Reply #44 on:** October 06, 2002, 01:06:09 PM »

Quote

Originally posted by DblTrubl
Last one. Sorry in advance if I killed anyones load times. I made em as small as I could while still keeping em readable. S!

Thanks! Had I had access to those materials, my arguement might have been more concise. S!