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Old 04-26-2014, 06:01 PM   #16
lnewqban
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Quote:
Originally Posted by scootrboi View Post
Gyroscopic aspect of wheels does not affect tipping. Surprise!




The cross section to diameter ratio of the tire makes the bike lean a little more or less, as well as the height of the combined CG (bike+rider).

Fat tires + low CG requires higher lean angle for same turn and speed.




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Old 04-26-2014, 11:08 PM   #17
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Quote:
Originally Posted by lnewqban View Post




The cross section to diameter ratio of the tire makes the bike lean a little more or less, as well as the height of the combined CG (bike+rider).

Fat tires + low CG requires higher lean angle for same turn and speed.



Now this is interesting. Particularly since I figured out those are not BMW logos. The phrase 'higher lean angle' seems awkward when it means leaning over more.
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Old 04-27-2014, 04:56 AM   #18
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why I prefer a shallow tread arc

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Originally Posted by lnewqban View Post
]
Thank you for sending this. This is exactly the kind of information I am looking for and can understand. Geometry, physics and diagrams! I am surprised at what it is telling me but it makes sense. This will help me to understand the effects of tire tread profiles and widths and steering effort, and the peculiarities of scooters.
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Old 04-27-2014, 07:15 AM   #19
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A question comes to mind: some scooters with a very low center of mass also have relatively little mass, and a full size human rider. The rider is a large percentage of the mass involved. The motor is small and light. This raises the center of mass significantly. Scooter tires are not very wide either. A motorcycle like a Goldwing or Harley has a lower center of mass than a scooter, I suspect. I wonder how it shuffles out with other motorcycles that are over 600 pounds.
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Old 04-27-2014, 10:23 AM   #20
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Err.. no.

Unless you are talking about a 70 or 80s Vespa, most modern scooters weigh as much as a bike, with lower center of gravity. The engine is inches off the ground, and you have very short wheelbases. 48 inch wheelbase for my '77 P200, 238 lbs. 8.5 inch ground clearance. Handles like you are on roller skates.

Some of them weigh more. The BMWs weigh a good 100lbs more than my F700GS, as well as longer wheelbases.
Those are pretty easy to out turn in the twisties.

Something in the middle, like a 300cc Jap or Korean bike is 350Lbs, 58 inch wheelbase, 16" wheels usually. They handle like a similar sized bike all told, like a CB360, as there are not many road bikes in the 300cc range anymore.
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Old 04-27-2014, 10:59 AM   #21
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Ok, so for example my Wee-Strom with its high CG and skinny 19" tire, do I have to lean over more to carry the same speed thru a corner as say a GSXR with fatter 17" rubber and lower CG?
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Old 04-27-2014, 11:30 AM   #22
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Ok, so for example my Wee-Strom with its high CG and skinny 19" tire, do I have to lean over more to carry the same speed thru a corner as say a GSXR with fatter 17" rubber and lower CG?
I think you have it backwards. When he says 'higher lean angle' he means leaning over further toward the ground. At least that is what the diagram says to me.
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Old 04-27-2014, 01:16 PM   #23
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Originally Posted by khager View Post
Ok, so for example my Wee-Strom with its high CG and skinny 19" tire, do I have to lean over more to carry the same speed thru a corner as say a GSXR with fatter 17" rubber and lower CG?
It is the other way around.
Lean angle is measured from a vertical line.

What really matters to absolute (system) lean angle (which generally differs form the angle the bike or frame leans) is the CG and the point of contact with the road.
How the bike and rider accommodate themselves to that fixed angle depends on tire profile, relative (to that profile) height of CG and hanging-off effect.

The mass or weight does not matter; light or heavy, the angle formed among the CG, point of contact and vertical is exactly the same for equal radius of turn and speed.
As you can see in the schematic below, the mass in the centrifugal force (horizontal force) cancels the mass in the weight (vertical force).



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Old 04-27-2014, 01:54 PM   #24
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Quote:
Originally Posted by khager View Post
Ok, so for example my Wee-Strom with its high CG and skinny 19" tire, do I have to lean over more to carry the same speed thru a corner as say a GSXR with fatter 17" rubber and lower CG?
Your Wee will lean slightly less than your GSXR for the same speed but the difference is very small. Furthermore, you wee will run out of clearance before your GSXR will, limiting cornering speed
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Old 04-27-2014, 01:56 PM   #25
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Quote:
Originally Posted by lnewqban View Post
It is the other way around.
Lean angle is measured from a vertical line.

What really matters to absolute (system) lean angle (which generally differs form the angle the bike or frame leans) is the CG and the point of contact with the road.
How the bike and rider accommodate themselves to that fixed angle depends on tire profile, relative (to that profile) height of CG and hanging-off effect.

The mass or weight does not matter; light or heavy, the angle formed among the CG, point of contact and vertical is exactly the same for equal radius of turn and speed.
As you can see in the schematic below, the mass in the centrifugal force (horizontal force) cancels the mass in the weight (vertical force).



What influence does the wheelbase have?
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Old 04-27-2014, 07:43 PM   #26
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Quote:
Originally Posted by scootrboi View Post
What influence does the wheelbase have?
As far as I know, no influence.
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Old 04-27-2014, 07:48 PM   #27
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Originally Posted by scootrboi View Post
What influence does the wheelbase have?
Here's a thread discussing that issue. http://advrider.com/forums/showthread.php?t=709177
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Old 04-28-2014, 08:36 PM   #28
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Your Wee will lean slightly less than your GSXR for the same speed but the difference is very small. Furthermore, you wee will run out of clearance before your GSXR will, limiting cornering speed
Thanks, I never was good at physics..
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Old 04-29-2014, 06:32 AM   #29
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Quote:
Originally Posted by lnewqban View Post
It is the other way around.
Lean angle is measured from a vertical line.

What really matters to absolute (system) lean angle (which generally differs form the angle the bike or frame leans) is the CG and the point of contact with the road.
How the bike and rider accommodate themselves to that fixed angle depends on tire profile, relative (to that profile) height of CG and hanging-off effect.




Now when a rider starts to move his center-line inside the bikes center-line (Especially the upper body) that has a great impact on the Combined center of gravity, and moves that in so it is more in line or even inside the line from the contact patch.
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Old 04-29-2014, 08:20 PM   #30
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Originally Posted by outlaws justice View Post
Now when a rider starts to move his center-line inside the bikes center-line (Especially the upper body) that has a great impact on the Combined center of gravity, and moves that in so it is more in line or even inside the line from the contact patch.
The Combined center of gravity remains in the same position.
What the rider does by moving his CG in is pushing the bike out a couple of degrees (more vertically).
The lateral forces on the contact patches remain the same, but the suspension gains those couple of degrees to work just a little better.

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