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subvetSSN606
Senior Member
418 Posts
[Mentor]
Ellettsville, IN
USA
Suzuki
800 Intruder
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 Posted - 10/22/2005 : 7:24 PM
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James,
I'm having a discussion elsewhere about the advantages/disadvantages of hanging off in a curve. Some people seem to think that hanging off gives one better traction. I contend that it does not.
Seems to me that for a given radius turn at a given speed:
1. The lateral force is the same.
2. The vertical force is the same.
3. The effective lean angle is the same. (regardless of what you do with your body)
4. The forces on the tire are applied along the effective lean angle (from the center of gravity to the contact patch)
Am I wrong?
My concern is that if I am correct, then those that think that leaning off will give them better traction due to the bike being more upright are putting themselves (and anyone else they convince) in danger.
Anyway, you are far better at presenting this type of information than I. I'd very much appreciate seeing your take on this so I can either eat my hat or refer folks to your discussion of it.
Thanks,
Tom
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Edited by - subvetSSN606 on 10/22/2005 7:26 PM |
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James R. Davis
 Administrator
14410 Posts
[Mentor]
Houston, TX
USA
Honda
GoldWing 1500
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Posted - 10/22/2005 : 7:58 PM
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You are absolutely correct in your analysis. The forces on the tire are the same at any given speed and curve radius.
The advantage of hanging off is merely low-side clearance gained - traction is not changed at all. Indeed, your contact patch width is marginally smaller when hanging off but, I assume you understand, that does NOT mean either more or less traction. |
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subvetSSN606
Senior Member
418 Posts
[Mentor]
Ellettsville, IN
USA
Suzuki
800 Intruder
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Posted - 10/22/2005 : 10:11 PM
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Thank you!
At least I am now more confident that I am not missing something, and propounding bad information.
Yes, I do understand... area is in both the numerator and denominator and cancels out.
And that was exactly the point I had been trying to make, that adding clearance to the point where you started dragging parts, or theoretically clearance to running out of the "business" part of the tire (although I think that's unlikely and would be a pretty poor tire design) was the only advantage to hanging off. Barring those two possibilities, you're going to lose traction at the same point, regardless of whether you are hanging off or not.
I think the misunderstanding comes from the oft stated concept of "go through a low traction situation as straight up as you can." And folks think bike angle, not effective angle. The ONLY way to reduce the lateral force on the bike through a curve is to SLOW DOWN! The only really SAFE way to reduce the lateral force the bike is going to experience in the curve is to slow down BEFORE THE CURVE!
Thanks again,
Tom
(PS. Should you have time and feel so inclined, I'd still love to see you do one of your articles on this). |
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nolaandy
Starting Member
8 Posts
New Orleans, Louisiana
USA
Suzuki
SV-650
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Posted - 02/19/2006 : 9:17 PM
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I disagree with one part of the above discussion. One reason to hang off and stand the bike up a bit is to present a more stable contact patch to the pavement. In extreme leans you can run out of stable tread.
There is another factor and that is steering feel. As a bike leans over farther changes in steering angle can have an inordinant effect (oversteering). Standing the bike up a bit can increase the feel and make steering corrections easier to perform.
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SkizitZX10R
Starting Member
3 Posts
Titusville, FL
USA
Kawasaki
2005 ZX-10R
Peer Review:
2
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Posted - 02/21/2006 : 2:54 AM
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Idealy, if you want to remain as stable as possible around any corner, be it on a bike or in a car, you want the total vehicle height to be as low to the ground as possible. Next, you want the center of mass to be as close to the center of rotation as possible, as well.
Here is a diagram...
The orange dot represents a fictional, but approximate location for the center of mass, and the blue dot represents where the center of mass may be if Mr. Bostrom were sitting up on the seat moreso.
As you can see, the angle of the orange line to the ground (A) is much less than the angle of the blue line and the ground. And, by properly balancing A, with B, you can obtain your best speed through a curve.
The variables change rapidly with velocity and curve intensity, but you can get a general feel for what I am trying to say. With this diagram, also, you can see another important fact. If your bike is tending to go towards the inside of a constant curve (fixed radius!), then you need to maintain your center of mass and go quicker, or maintain the same speed and raise the center of mass. Likewise, if the bike drifts towards the outside of the corner, you need to either lower your center of mass more and maintain speed, or you need to maintain your center of mass and slow down.
You notice racers, as they come into curves, they gradually get down to their lowest center of mass at the apex of the curve, then gradually raise the center of mass back up as they leave the curve. This is perfectly choreographed allowing them to manipulate the throttle at will by adjusting their CofM, or vise versa.
By the way, traction is traction. It is based on a ratio of acting forces and the negative forces friction can apply before the applied force exceeds the negative frictional force. "Traction" can be assumed as your limit of frictional resistance. If you consume all your traction, your leathers get to do their work. The diagram below gives a simple explanation of friction versus applied force.
The green arrows indicate points in the ratio where the negative frictional force is still greater than the applied force. The red arrow indicates the opposite. Just a tiny bit right of the "harmony" point is where slight drift begins to occur, and just beyond that is the pavement. I could talk about this stuff all day long..I'll shut up now.
Hope this helps at all.
Nice forum by the way...finally nice to see a bike forum with a physics/theory forum on it!
-Jason |
Edited by - SkizitZX10R on 02/21/2006 3:10 AM |
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James R. Davis
Administrator
14410 Posts
[Mentor]
Houston, TX
USA
Honda
GoldWing 1500
Peer Review:
1
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Posted - 02/21/2006 : 5:14 AM
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Bravo! Here you have spoken to the readers with added value as your intent and from their perspective.
I would like to respectfully suggest that your initial diagram and discussion are incomplete and, as a result, yield a false impression. That is, angle 'A' as you point out is correct but it is NOT determined by the posture of the rider. It is absolutely determined by the speed the rider and bike are moving and the radius of the turn they are making. If he were to sit back up on the seat but not change either his speed or the radius he is turning then the new CG would be higher, of course, but it would still (no matter what the rider's posture is) describe angle 'A' (orange), not the angle described by the blue line.
That is, 'mg' would remain 'mg' and 'mv^2/R' would still be 'mv^2/R'. No? In other words, if the rider were not to lean into the turn as far as shown then his bike would, perforce, lean farther into it.
Further, relative to being 'stable' ... your argument suggests that the lower the CG is relative to the ground the more 'stable' the bike will be. Is that right? So, when the bike is vertical and thus having the highest possible CG it would then be least stable? Is it your contention that riding in a straight line, vertical, is less stable than when in any other configuration? Recognizing that you limited your remarks to a bike in a turn, is a bike that has a lean angle of 5 degrees and, thus a higher CG, less stable than a bike that is leaned over at 45 degrees?
'Stable' is an elusive concept - but I think it is fair to say that for all practical purposes so long as the bike and rider are describing lean angle 'A' they are stable in that turn.
I delight in seeing your graphics. They add value and make discussions accessible to far more people than simply words, no matter how well crafted those words are.
Again, bravo! |
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James R. Davis
Administrator
14410 Posts
[Mentor]
Houston, TX
USA
Honda
GoldWing 1500
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Posted - 02/22/2006 : 6:53 AM
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I think everybody here understands that you can consume more traction than is available and, thus, cause tire slippage. What I am having trouble with is your diagram which seems to imply that you can EITHER have less frictional force than applied force or more frictional force than applied force - that is, that you can ever be at a point other than 'harmony'. Again, the concept of consuming more traction than is available is easily understood, but to suggest that forces are EVER other than equal and opposite seems rather out of place in a discussion about physics and the theoretical.
This can read like nitpicking and I do not want that to be the case. I all too frequently take shortcuts in my terminology in this forum, sometimes deliberately, so I would like not to be seen taking potshots at your choice of words. For example, in my immediately prior message talked about the lean angle being absolutely determined by 'speed' and radius of the curve when we both know that I should have used the word 'velocity' instead. But our readers accept the more common term 'speed' because it is just that, common.
When I talk about tires I use the word 'skid' to mean a loss of traction in the direction of travel. I use the word 'slide' to mean a loss of traction in a lateral direction. The word 'slip' when talking about the difference between the speed of the bike and the tire speed (at the contact patch) in any direction (including rotational.) And, finally, 'drift' to mean an unintentional (usually) widening of a turn. You seem to use the word 'drift' the way I would use 'slip'. Is that correct?
If so, then I would argue that the application of ANY amount of torque (positive or negative) MUST cause tire slip. For example, when you apply your brakes you immediately begin to reduce the angular velocity of the wheel but inertia attempts to keep the vehicle moving and, thus, the tire rubber is deformed. In other words, the angular velocity of the circumference of the tire will no longer be the same as that of the wheel rim until torque is no longer applied. That is 'slip'. Would you call that 'drift'?
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tasoss
Starting Member
2 Posts
thessaloniki, macedonia
Greece
Yamaha
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Posted - 06/16/2007 : 4:12 PM
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hello and nice to meet you.
i have just a simple question.
mv^2/R is supposed to act inward or outward the curve?
as much as i have read it is supposed to act inward.
so this picture is correct?
thank you in advance! :)
ps:in simple english which are the advantages of hanging off? |
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COOLTOY
Junior Member
34 Posts
Liberty, UT
USA
Suzuki
DL 650
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Posted - 06/26/2007 : 2:36 PM
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Well, here then lies a critical question I have with this idea that lean angle does not affect traction.
I would interpret this to mean that I can apply the same amount of throttle when leaned over 45 degrees, as I can when leaned over 15 degrees at a given speed; say 50 mph.
quote:
You are absolutely correct in your analysis. The forces on the tire are the same at any given speed and curve radius.
Also, there are three factors that create force on a tire: Speed, curve radius, and path of travel. Essentially path of travel could be considered radius, but the two are not mutually exclusive. In a corner with a 90 degree radius, there are many different paths of travel that will change the forces placed on a tire.
Your thoughts?
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James R. Davis
Administrator
14410 Posts
[Mentor]
Houston, TX
USA
Honda
GoldWing 1500
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Posted - 06/26/2007 : 2:50 PM
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There has been a radical disconnect demonstrated here.
Nobody has claimed what you conclude or even impied that. My argument was that forces ALWAYS are balanced. For example, the amount of centrifugal force is always equal and opposite to the amount of centripetal force.
Surely you don't imagine that I was saying that centrifugal force is always equal to gravity (weight), for example. They are orthogonal to start with and are not in any way related.
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COOLTOY
Junior Member
34 Posts
Liberty, UT
USA
Suzuki
DL 650
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Posted - 06/26/2007 : 3:08 PM
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quote:
You are absolutely correct in your analysis. The forces on the tire are the same at any given speed and curve radius.
The advantage of hanging off is merely low-side clearance gained - traction is not changed at all. Indeed, your contact patch width is marginally smaller when hanging off but, I assume you understand, that does NOT mean either more or less traction.
I am just trying to gain a better understanding of your statement above.
I am assuming this statement is relating to total traction available of which I agree. So, while the total traction available may not change, the change in lean angle does provide less traction being used for turning, and more to be available for accellerating? |
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Sox Fan
Senior Member
419 Posts
[Mentor]
Kerhonkson, NY
USA
Suzuki
DL 650
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Posted - 06/26/2007 : 3:21 PM
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I hope this isn't muddying the waters, but I did want to add something here. Lee Parks, in his book Total Control, makes the case that lean angle does affect traction, but it's not because it affects friction the way some riders think it does. Here's the quote, from page 16 (emphasis added in bold by me):
"Lean angle also affects grip, but not for the reasons you might think. At higher lean angles, motorcycle suspension becomes less efficient because the moving parts are no longer perpendicular to the the forces being applied to them. In essence, the spring rates become progressively stiffer, and the sideways forces cause sliding parts to flex against one another causing additional friction. To counter these inefficiencies, motorcycle engineers design in a "tuned" amount of chassis and tire flex. This is helpful because at maximum lean the frame and tire sidewalls are at a better angle to absorb bumps in the road than the suspension system. Unfortunately, despite the engineers' best efforts, the total pizza available still gets slightly smaller as lean angles increase."
If I understand this correctly, the "sliding parts" to which he's refering are suspension components, not tires sliding on the road surface.
I think I understand what he's saying, but I also think that this concept probably only really applies in extreme lean angles. At the speeds most of us ride, it sounds like the amount of difference hanging off might make is negligible at best. Besides, if you're riding on open public roads at speeds that cause you to need maximum lean angles, you may be more interested in excitement than in safety. |
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dhalen32
Moderator
566 Posts
[Mentor]
Omaha, NE
USA
Yamaha
FJR 1300
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Posted - 08/15/2007 : 1:09 PM
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quote:
Originally posted by subvetSSN606
James,
I'm having a discussion elsewhere about the advantages/disadvantages of hanging off in a curve. Some people seem to think that hanging off gives one better traction. I contend that it does not.
Seems to me that for a given radius turn at a given speed:
1. The lateral force is the same.
2. The vertical force is the same.
3. The effective lean angle is the same. (regardless of what you do with your body)
4. The forces on the tire are applied along the effective lean angle (from the center of gravity to the contact patch)
Am I wrong?
My concern is that if I am correct, then those that think that leaning off will give them better traction due to the bike being more upright are putting themselves (and anyone else they convince) in danger.
Anyway, you are far better at presenting this type of information than I. I'd very much appreciate seeing your take on this so I can either eat my hat or refer folks to your discussion of it.
Thanks,
Tom
I have read (or heard) that the major benefits of hanging off a racing motorcycle include: more cornering clearance for things that you don't want dragging on the pavement, better suspension action due to those components being closer to perpendicular to the pavement and an ability to start accelerating sooner due to less of the available traction being consumed by cornering side force. I suppose there is also probably more normal force and thus more traction the more perpendicular the bike is to the pavement too.
Dave
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James R. Davis
Administrator
14410 Posts
[Mentor]
Houston, TX
USA
Honda
GoldWing 1500
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Posted - 08/15/2007 : 1:32 PM
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quote:
... and an ability to start accelerating sooner due to less of the available traction being consumed by cornering side force. I suppose there is also probably more normal force and thus more traction the more perpendicular the bike is to the pavement too.
I can see why you may think these are true though they are not.
Your cornering side forces are not a function of lean angle. They are a function of velocity and radius of the turn (without regard for cross winds.)
Similarly, normal forces (weight) are the same with a lean or without. |
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onesportbikerider
Starting Member
4 Posts
Somewhere In, FL
USA
Kawasaki
ZZR600J
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Posted - 08/28/2007 : 10:21 AM
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I think the picture that SkizitZX10R submitted was great, however the description was all wrong.
Below is depicted a rider going around a corner at high speed:
[The original img file no longer exists or was of a format this site does not support - deleted]
By hanging off the bike while in the turn the rider effectively lowers the combined center of gravity of both the cycle and rider. This presents a shorter leverage arm (3) for the centripital forces (6)to act upon. In short, we all know (hopefully) that when going around a corner at high speed that the bike needs to lean into the turn. Why? Because the centripital forces are pushing on the bike (and rider) and if it isn't leaning into the turn it would fall over (high side).
So if you want to go faster around a corner and keep the same bike lean angle (A) you could do so by hanging off the bike (effectively increasing your effective lean angle).
If you want to go faster and not hang off the bike you will have to lean over even more (B) to counter the centripetal forces.
Forces (2) and (4) cannot be compensated for by hanging off. The rubber is in charge here. The faster you go, the more lateral (sideways) pressure you're putting on the tire. Whether you are hanging off or not, the tire will break away if pushed hard enough.
That being said. There is some very welcome and important insurance gained by having the bike "straighter" in the corner in case the tires do break away. And that is,... If the tires do slide, the amount of leverage afforded to the downward force (originating from the CG) is less than it would be if the bike were leaning over more and you weren't hanging off.
In such an instance the rider has much more leverage, room and time to recuperate from the slide.
Say for example; the bike was rounding a corner on a wet road, but because the rider was hanging off, the bike lean angle was 90 degrees (dead straight). If the tires did break away, the bike is already upright, and the chances of slamming into the ground (low side) are relatively low.
Now, say the bike was rounding the corner on a wet road leaned over at 30 degrees. The rider was already leaned over at maximum, so there is no leverage, room, or time for recovery (he was already touching the ground).
If you are going that fast you absolutely NEED to hang off to make sure you have as much tread as possible on the ground.
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Edited by - onesportbikerider on 03/10/2009 9:12 AM |
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James R. Davis
Administrator
14410 Posts
[Mentor]
Houston, TX
USA
Honda
GoldWing 1500
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Posted - 08/28/2007 : 11:32 AM
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With respect, and with full knowledge that you understand what you are talking about, there is an assumption in your analysis that has led you down an unfortunate path to a conclusion that is factually wrong.
quote:
By hanging off the bike while in the turn the rider effectively lowers the combined center of gravity of both the cycle and rider. This presents a shorter leverage arm (3) for the centripital forces (6)to act upon.
Your assumption in that quote is that the combined motorcycle/biker lean angles (A and B) reflect the same speed in that turn. They do not, definitionally.
The combined lean angle is determined, absolutely, by the speed of the vehicle and the radius of the turn it is in (discounting any crosswind effects.)
Whether the rider is hanging off or not, the lean angle is exactly the same. Yes, the height of the CG varies with rider position, but that does NOT change the angle. Thus, the relationship between height of the CG to the length of the distance that CG is from the contact patch is the same in all cases.
In other words, your conclusion is false and is based upon a faulty assumption.
Similarly, your discussion about traction is not accurate. Available traction while leaned over is USUALLY HIGHER than when riding vertical. This, because tire compounds, particularly for racing tires, are softer off center than they are mid track specifically to increase their performance (traction) while leaned over at the expense of tire life.
It is true that there is a greater demand for traction when the combined lean angle increases because of lateral acceleration forces, but as I earlier pointed out, the combined lean angle is EXACTLY THE SAME regardless of whether or not you are hanging off the bike in the turn. |
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twc
Advanced Member
627 Posts
[Mentor]
Fort Collins, CO
USA
Harley-Davidson
Electra Glide Ultra
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Posted - 08/28/2007 : 12:59 PM
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Jim, I'm going to need a little help to resolve the apparent contradiction in the following two quotes. Since you're the author of both, I think you're the man for the job!
My understanding of hanging off is that it allows the bike to stand up higher for a given speed than would be the case if you didn't hang off. In a racing situation, that translates to be able to take a corner faster when you're hanging off. What am I missing?
quote:
Originally posted by James R. Davis
Whether the rider is hanging off or not, the lean angle is exactly the same. Yes, the height of the CG varies with rider position, but that does NOT change the angle.
quote:
From Tip #45 by James R. Davis
There are three things that can be done as soon as you hear/feel a peg scrape:
- Increase throttle - (but note that you are already close to sliding and ANY increase in speed can be all she wrote)
- Counter-steer away from the dragging peg - (widen the turn)
- Shift body weight towards the dragging peg - (that is not a misprint)
Each of these actions tends to straighten the bike up. Any one of them will 'cure' the problem and is sufficient by itself. You can, of course, do two or all three of these things at the same time.
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James R. Davis
Administrator
14410 Posts
[Mentor]
Houston, TX
USA
Honda
GoldWing 1500
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Posted - 08/28/2007 : 1:20 PM
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Happy to try to clarify this for you.
It is the lean angle of the combined motorcycle and rider that is determined by speed and radius, not that of just the bike.
So, for any given speed and radius that angle is what it is regardless of the position of the rider.
For example, let's say that your bike can lean over at 45 degrees before it begins to drag hard parts. Now let's assume that on a particular turn you find that while sitting in-line with the bike (not hanging off) and traveling at 50 MPH the bike is leaning over at 45 degrees. You are going, then, as fast as possible without changing your body position.
So, you hang-off into the turn. Now your combined lean angle is still 45 degrees, but you are leaning more than 45 degrees and your bike is leaning less than 45 degrees. Thus, the bike is no longer dragging hard parts. That means that you can then further increase your speed in that turn until the lean angle OF THE BIKE is once again 45 degrees. Let's say that you can now make that turn at 60 MPH if you hang-off while in that turn.
In other words, without hanging off the lean angle of the bike is the same as the lean angle of you and the bike and when you are hanging off the lean angle of the bike itself is less than the lean angle of the combined bike and rider. What determines how fast you can go in a turn is the lean angle of the bike, not that of the combined bike and rider. |
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twc
Advanced Member
627 Posts
[Mentor]
Fort Collins, CO
USA
Harley-Davidson
Electra Glide Ultra
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Posted - 08/28/2007 : 2:02 PM
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quote:
Originally posted by James R. Davis
It is the lean angle of the combined motorcycle and rider that is determined by speed and radius, not that of just the bike...
That makes perfect sense. Thanks!
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onesportbikerider
Starting Member
4 Posts
Somewhere In, FL
USA
Kawasaki
ZZR600J
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Posted - 08/28/2007 : 2:09 PM
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James, I think you need to reread my post a little more carefully.
quote:
Originally posted by James R. DavisThe combined lean angle is determined, absolutely, by the speed of the vehicle and the radius of the turn it is in (discounting any crosswind effects.)
I mentioned nothing about the combined angle of the bike and rider changing because the rider does, or does not hang off the bike (the effective lean angle). This cannot be changed. As I have stated.
What can be changed is the angle of the motorcycle with respect to the road.
quote:
Originally posted by James R. Davis Yes, the height of the CG varies with rider position, but that does NOT change the angle.
You are correct in that the diagram is a bit confusing. However, what it is supposed to express as you have just stated, is that a higher CG requires greater bike lean angle to compensate for centripetal forces.
quote:
Originally posted by James R. DavisSimilarly, your discussion about traction is not accurate. Available traction while leaned over is USUALLY HIGHER than when riding vertical. This, because tire compounds, particularly for racing tires, are softer off center than they are mid track specifically to increase their performance (traction) while leaned over at the expense of tire life.
Umm, did you read my post. Or do you regularly just jump on your soapbox regardless of what anyone else said.
Did I make any mention towards the point that you have less traction at normal lean angles.
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Edited by - onesportbikerider on 03/10/2009 9:02 AM |
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James R. Davis
Administrator
14410 Posts
[Mentor]
Houston, TX
USA
Honda
GoldWing 1500
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Posted - 08/28/2007 : 2:19 PM
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We are certainly in agreement with what you said before you edited your post.
If I misread what you had to say, I apologize. But the thread has just now cleared up those issues for some people as a result of our messages. |
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Re: Hanging Off