Load transfer question
09-19-2005, 10:05 AM
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Load transfer question
Load transfer question
For arguments sake let’s assume the following:
1) Total rear roll resistance of 600 lbs/inch of rear suspension travel.
2) The static weight on each rear tire is 400 lbs.
3) The car’s rear suspension compresses 1 inch when cornering at the limit. Thus there is 600lbs of load transfer onto the outside rear tire.
This car starts to corner and 400 lbs of load is transferred from the inside rear tire to the outside rear tire. This leaves zero load on the outside rear tire. The car continues to speed up in the turn reaching the limit of adhesion and now there is 600 lbs of load on the outside rear tire. Were does this additional 200lbs of load come from? Does it all come off the inside front tire? Also if you have a rear anti-waybar it can actually push the inside rear tire up into the tire well. I guess this would be a negative load on the inside rear tire?
For arguments sake let’s assume the following:
1) Total rear roll resistance of 600 lbs/inch of rear suspension travel.
2) The static weight on each rear tire is 400 lbs.
3) The car’s rear suspension compresses 1 inch when cornering at the limit. Thus there is 600lbs of load transfer onto the outside rear tire.
This car starts to corner and 400 lbs of load is transferred from the inside rear tire to the outside rear tire. This leaves zero load on the outside rear tire. The car continues to speed up in the turn reaching the limit of adhesion and now there is 600 lbs of load on the outside rear tire. Were does this additional 200lbs of load come from? Does it all come off the inside front tire? Also if you have a rear anti-waybar it can actually push the inside rear tire up into the tire well. I guess this would be a negative load on the inside rear tire?
09-19-2005, 10:16 AM
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Re: Load transfer question (577HondaPrelude)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 577HondaPrelude »</TD></TR><TR><TD CLASS="quote">... Were does this additional 200lbs of load come from? </TD></TR></TABLE>
It's rather obvious don't you think?
From the Preload.
Scott, who says the answer to your question is in the error in the question - 400 transfers from inside to outside, you lift, and that's it, the outside rear is done - unless you run it over a hole or a bump...or accelerate/decelerate longitudinally...
It's rather obvious don't you think?
From the Preload.
Scott, who says the answer to your question is in the error in the question - 400 transfers from inside to outside, you lift, and that's it, the outside rear is done - unless you run it over a hole or a bump...or accelerate/decelerate longitudinally...
09-19-2005, 10:28 AM
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Re: Load transfer question (RR98ITR)
So then what happens if your at the point were you have transferred 400lbs from the inside rear to the outside rear, then the car speeds up in the same radius turn?
09-19-2005, 10:35 AM
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Re: Load transfer question (577HondaPrelude)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 577HondaPrelude »</TD></TR><TR><TD CLASS="quote">So then what happens if your at the point were you have transferred 400lbs from the inside rear to the outside rear, then the car speeds up in the same radius turn? </TD></TR></TABLE>
Then some load will transfer from the front to the rear.
Where exactly is goes depends.
That inside rear lift is due to the weight transferred (post lift) from the inside front to the outside front (picture the chassis rotating about a diagonal running from the outside rear to the inside front).
If you got alot of lift and you're transferring just a little rearward it'll land on the outside rear. Just a little lift and some of it may wind up on the inside rear.
Scott, who has transferred all of his load onto the jack pads...
Then some load will transfer from the front to the rear.
Where exactly is goes depends.
That inside rear lift is due to the weight transferred (post lift) from the inside front to the outside front (picture the chassis rotating about a diagonal running from the outside rear to the inside front).
If you got alot of lift and you're transferring just a little rearward it'll land on the outside rear. Just a little lift and some of it may wind up on the inside rear.
Scott, who has transferred all of his load onto the jack pads...
09-19-2005, 10:43 AM
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Re: Load transfer question (RR98ITR)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote »</TD></TR><TR><TD CLASS="quote">Scott, who says the answer to your question is in the error in the question - 400 transfers from inside to outside, you lift, and that's it, the outside rear is done - unless you run it over a hole or a bump...or accelerate/decelerate longitudinally... </TD></TR></TABLE>
then what you said here is not true, the outside rear is not done, it can in fact have more load transferred to it. This load comes off the inside front tire only right?
if all the additional load (post lift) was to go from the inside front to the outside front only then the front suspension would compress more while the rear suspension would not compress any farther. If this was true it would make the car pitch forward from a force acting on the center of gravity, and I don't think that's possible....or maybe it is and that's the problem with my thinking.
Modified by 577HondaPrelude at 2:55 PM 9/19/2005
then what you said here is not true, the outside rear is not done, it can in fact have more load transferred to it. This load comes off the inside front tire only right?
if all the additional load (post lift) was to go from the inside front to the outside front only then the front suspension would compress more while the rear suspension would not compress any farther. If this was true it would make the car pitch forward from a force acting on the center of gravity, and I don't think that's possible....or maybe it is and that's the problem with my thinking.
Modified by 577HondaPrelude at 2:55 PM 9/19/2005
09-19-2005, 11:05 AM
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Re: Load transfer question (577HondaPrelude)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 577HondaPrelude »</TD></TR><TR><TD CLASS="quote">
then what you said here is not true, the outside rear is not done, it can in fact have more load transferred to it. This load comes off the inside front tire only right?</TD></TR></TABLE>
You haven't mentioned anything about front roll stiffness. The distribution front/rear will help determine whether load will transfer from the inside front to the outside rear or visa versa. If you don't give info about the whole car then we have to assume were looking at a single axle. In that case, the rear won't compress 1".
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote »</TD></TR><TR><TD CLASS="quote">if additional load (post lift) was to go from the inside front to the outside front only then the front suspension would compress more while the rear suspension would not compress any farther. If this was true it would make the car pitch forward from a force acting on the center of gravity, and I don't think that's possible....or maybe it is and that's the problem with my thinking.</TD></TR></TABLE>
This car most likely has an inclined roll axis, which determines the direction of rotation. A car with a forward inclined axis will transfer load longitudinally and also pitch under a purely lateral acceleration.
then what you said here is not true, the outside rear is not done, it can in fact have more load transferred to it. This load comes off the inside front tire only right?</TD></TR></TABLE>
You haven't mentioned anything about front roll stiffness. The distribution front/rear will help determine whether load will transfer from the inside front to the outside rear or visa versa. If you don't give info about the whole car then we have to assume were looking at a single axle. In that case, the rear won't compress 1".
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote »</TD></TR><TR><TD CLASS="quote">if additional load (post lift) was to go from the inside front to the outside front only then the front suspension would compress more while the rear suspension would not compress any farther. If this was true it would make the car pitch forward from a force acting on the center of gravity, and I don't think that's possible....or maybe it is and that's the problem with my thinking.</TD></TR></TABLE>
This car most likely has an inclined roll axis, which determines the direction of rotation. A car with a forward inclined axis will transfer load longitudinally and also pitch under a purely lateral acceleration.
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09-19-2005, 11:08 AM
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Re: Load transfer question (577HondaPrelude)
I was just thinking roll stiffness to be much less in the front...
ok, after thinking some more about it. A side force can in fact make the car tilt to the front and the load can mostly go from the inside front to the outside front post lift. It's starting to come clear to me now... thanks!
Modified by 577HondaPrelude at 3:22 PM 9/19/2005
ok, after thinking some more about it. A side force can in fact make the car tilt to the front and the load can mostly go from the inside front to the outside front post lift. It's starting to come clear to me now... thanks!
Modified by 577HondaPrelude at 3:22 PM 9/19/2005
09-19-2005, 11:09 AM
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Re: Load transfer question (577HondaPrelude)
What I said is true.
When you turn load moves laterally.
When you use gas or brakes it moves between front and rear.
In pure roll once the inside rear lifts, all remaining load transfer takes place between the two front wheels.
And if you were to add acceleration then you'd transfer some weight from front to rear - very likely off of both front wheels.
As you roll (post lift) the inside front rises and the outside front compresses.
Keep thinking about it.
Scott, who's kaa is subjected to a steady 1.0 g vertical load...
When you turn load moves laterally.
When you use gas or brakes it moves between front and rear.
In pure roll once the inside rear lifts, all remaining load transfer takes place between the two front wheels.
And if you were to add acceleration then you'd transfer some weight from front to rear - very likely off of both front wheels.
As you roll (post lift) the inside front rises and the outside front compresses.
Keep thinking about it.
Scott, who's kaa is subjected to a steady 1.0 g vertical load...
09-19-2005, 11:31 AM
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Re: Load transfer question (RR98ITR)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RR98ITR »</TD></TR><TR><TD CLASS="quote">What I said is true.
When you turn load moves laterally.
When you use gas or brakes it moves between front and rear.
In pure roll once the inside rear lifts, all remaining load transfer takes place between the two front wheels.
And if you were to add acceleration then you'd transfer some weight from front to rear - very likely off of both front wheels.
As you roll (post lift) the inside front rises and the outside front compresses.
Keep thinking about it.
Scott, who's kaa is subjected to a steady 1.0 g vertical load...</TD></TR></TABLE>
Load can transfer longitudinally under pure roll, too.
Chris - who is leaving to vertically transfer a load, but will be back in 15-20 minutes.
When you turn load moves laterally.
When you use gas or brakes it moves between front and rear.
In pure roll once the inside rear lifts, all remaining load transfer takes place between the two front wheels.
And if you were to add acceleration then you'd transfer some weight from front to rear - very likely off of both front wheels.
As you roll (post lift) the inside front rises and the outside front compresses.
Keep thinking about it.
Scott, who's kaa is subjected to a steady 1.0 g vertical load...</TD></TR></TABLE>
Load can transfer longitudinally under pure roll, too.
Chris - who is leaving to vertically transfer a load, but will be back in 15-20 minutes.
09-19-2005, 11:36 AM
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Re: Load transfer question (GSpeedR)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by GSpeedR »</TD></TR><TR><TD CLASS="quote">
Load can transfer longitudinally under pure roll, too.
</TD></TR></TABLE>
Tell us about it.
Scott, who is all about being open minded...just don't talk to me about reactive kinematics tm...
Load can transfer longitudinally under pure roll, too.
</TD></TR></TABLE>
Tell us about it.
Scott, who is all about being open minded...just don't talk to me about reactive kinematics tm...
09-19-2005, 11:36 AM
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Re: Load transfer question (RR98ITR)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RR98ITR »</TD></TR><TR><TD CLASS="quote">What I said is true.
When you turn load moves laterally.
When you use gas or brakes it moves between front and rear.
In pure roll once the inside rear lifts, all remaining load transfer takes place between the two front wheels.</TD></TR></TABLE>
in your "pure roll" example, why wouldnt the outside rear wheel share part of the load transfer from the inside front tire? surely, the NET roll transfer from left to right is equal, but not solely on the outside FRONT wheel just because the inside rear wheel is lifted.
so then there still is a front/back load transfer, even if the rear inside wheel is lifted.
tyson, who just got sucked into another useless suspension theory thread.
When you turn load moves laterally.
When you use gas or brakes it moves between front and rear.
In pure roll once the inside rear lifts, all remaining load transfer takes place between the two front wheels.</TD></TR></TABLE>
in your "pure roll" example, why wouldnt the outside rear wheel share part of the load transfer from the inside front tire? surely, the NET roll transfer from left to right is equal, but not solely on the outside FRONT wheel just because the inside rear wheel is lifted.
so then there still is a front/back load transfer, even if the rear inside wheel is lifted.
tyson, who just got sucked into another useless suspension theory thread.
09-19-2005, 11:39 AM
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Re: Load transfer question (Tyson)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Tyson »</TD></TR><TR><TD CLASS="quote">
in your "pure roll" example, why wouldnt the outside rear wheel share part of the load transfer from the inside front tire? surely, the NET roll transfer from left to right is equal, but not solely on the outside FRONT wheel just because the inside rear wheel is lifted.
so then there still is a front/back load transfer, even if the rear inside wheel is lifted.</TD></TR></TABLE>
Let's let Chris 'splain that one too.
Scott, who is will get lunch and come back for some readin'...
in your "pure roll" example, why wouldnt the outside rear wheel share part of the load transfer from the inside front tire? surely, the NET roll transfer from left to right is equal, but not solely on the outside FRONT wheel just because the inside rear wheel is lifted.
so then there still is a front/back load transfer, even if the rear inside wheel is lifted.</TD></TR></TABLE>
Let's let Chris 'splain that one too.
Scott, who is will get lunch and come back for some readin'...
09-20-2005, 07:34 AM
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Re: Load transfer question (RR98ITR)
Here's my thoughts (which I am less confident of than I was yesterday):
When you incline the roll-axis with respect to the inertial axes of the vehicle, you are coupling the effects of roll and yaw (roll-yaw coupling). If you inclined the roll axis 90 degrees it would be parallel to the yaw axis, so this is true. However, this by itself doesn't cause longitudinal load transfer. For the car to transfer load longitudinally (and pitch) it must have a rotational acceleration about the pitch axis (which is a horizontal line going left to right). I believe SAE locates it at the CG, but a vehicle doesn't pitch about its CG when the tires are on the ground. The pitch axis is located fore or aft of the CG depending on the suspension (production cars are usually in front of the CG).
So for the car to pitch under pure roll, there must be a longitudinal or vertical force from the tires to cause a moment about the pitch axis. You won't get this from the rolling acceleration. However, the yawing moment is reacted only by the tire contact patches on the ground (yaw inertia nonwithstanding). If there is a longitudinal tire force (with respect to the vehicle inertial axes) then the vehicle will accelerate about the pitch axis. I don't have access to my tire data right now, and I don't remember if the "lateral" force produced by the tire due to a slip angle is perpendicular to the wheel or to the contact patch direction. If it's the latter then there is a longitudinal force component perpendicular to the pitch axis which will cause a rotational acceleration and hence pitch.
When you incline the roll-axis with respect to the inertial axes of the vehicle, you are coupling the effects of roll and yaw (roll-yaw coupling). If you inclined the roll axis 90 degrees it would be parallel to the yaw axis, so this is true. However, this by itself doesn't cause longitudinal load transfer. For the car to transfer load longitudinally (and pitch) it must have a rotational acceleration about the pitch axis (which is a horizontal line going left to right). I believe SAE locates it at the CG, but a vehicle doesn't pitch about its CG when the tires are on the ground. The pitch axis is located fore or aft of the CG depending on the suspension (production cars are usually in front of the CG).
So for the car to pitch under pure roll, there must be a longitudinal or vertical force from the tires to cause a moment about the pitch axis. You won't get this from the rolling acceleration. However, the yawing moment is reacted only by the tire contact patches on the ground (yaw inertia nonwithstanding). If there is a longitudinal tire force (with respect to the vehicle inertial axes) then the vehicle will accelerate about the pitch axis. I don't have access to my tire data right now, and I don't remember if the "lateral" force produced by the tire due to a slip angle is perpendicular to the wheel or to the contact patch direction. If it's the latter then there is a longitudinal force component perpendicular to the pitch axis which will cause a rotational acceleration and hence pitch.
09-20-2005, 07:40 AM
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Re: Load transfer question (GSpeedR)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by GSpeedR »</TD></TR><TR><TD CLASS="quote">... If it's the latter then there is a longitudinal force component perpendicular to the pitch axis which will cause a rotational acceleration and hence pitch. </TD></TR></TABLE>
Pure roll - you've got a throttle setting providing an equal and opposite longitudinal force at the contact patches.
Scott, who knows that in actual practice we've usually got more throttle on than that...but this is an academic exploration...
Pure roll - you've got a throttle setting providing an equal and opposite longitudinal force at the contact patches.
Scott, who knows that in actual practice we've usually got more throttle on than that...but this is an academic exploration...
09-20-2005, 08:04 AM
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Re: Load transfer question (RR98ITR)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RR98ITR »</TD></TR><TR><TD CLASS="quote">Pure roll - you've got a throttle setting providing an equal and opposite longitudinal force at the contact patches.
</TD></TR></TABLE>
Longitudinally, I don't think the resulting tire forces would cancel each other out, even though there was no long. force initially. So we started with a throttle that gives us pure roll, but this pure roll leads us to potential longitudinal tire forces (maybe) and thus we need a different throttle input or else the car pitches: an iterative process of sorts.
</TD></TR></TABLE>
Longitudinally, I don't think the resulting tire forces would cancel each other out, even though there was no long. force initially. So we started with a throttle that gives us pure roll, but this pure roll leads us to potential longitudinal tire forces (maybe) and thus we need a different throttle input or else the car pitches: an iterative process of sorts.
09-20-2005, 08:36 AM
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Re: Load transfer question (GSpeedR)
We're getting down to a might thin hair splitting aren't we?
We did start with a large log's worth of lateral force input parsed into pitch didn't we?
Maybe Tyson's been working on it and is just about ready to drop the bomb?
Scott, who thinks maybe it could work with Hydrolics...
We did start with a large log's worth of lateral force input parsed into pitch didn't we?
Maybe Tyson's been working on it and is just about ready to drop the bomb?
Scott, who thinks maybe it could work with Hydrolics...
09-20-2005, 09:16 AM
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Re: Load transfer question (RR98ITR)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RR98ITR »</TD></TR><TR><TD CLASS="quote">We're getting down to a might thin hair splitting aren't we?
We did start with a large log's worth of lateral force input parsed into pitch didn't we?
Maybe Tyson's been working on it and is just about ready to drop the bomb?
Scott, who thinks maybe it could work with Hydrolics...</TD></TR></TABLE>
Yeah. I'm pretty sure you won't get 200lb of forward transfer from the above.
I think the issue in the case of rear wheel lift, is that the roll axis is now pivoting sideways as the rear roll center migrates a lot more than the front (roll-pitch coupling!!!!!11). Now there is a significant source of pitch acceleration under a roll acceleration. Maybe that is what Tyson is hinting at? Or maybe Tyson gave up and let the morons have the thread.
Chris - hair splitter and member of Team ThreadJack
We did start with a large log's worth of lateral force input parsed into pitch didn't we?
Maybe Tyson's been working on it and is just about ready to drop the bomb?
Scott, who thinks maybe it could work with Hydrolics...</TD></TR></TABLE>
Yeah. I'm pretty sure you won't get 200lb of forward transfer from the above.
I think the issue in the case of rear wheel lift, is that the roll axis is now pivoting sideways as the rear roll center migrates a lot more than the front (roll-pitch coupling!!!!!11). Now there is a significant source of pitch acceleration under a roll acceleration. Maybe that is what Tyson is hinting at? Or maybe Tyson gave up and let the morons have the thread.
Chris - hair splitter and member of Team ThreadJack
09-20-2005, 09:55 AM
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Re: Load transfer question (Tyson)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Tyson »</TD></TR><TR><TD CLASS="quote">what about droop?</TD></TR></TABLE>
What about it?
Scott, who takes it as a sign of encouragement that Tyson returned to the thread...get's Chris off the hook for now..
What about it?
Scott, who takes it as a sign of encouragement that Tyson returned to the thread...get's Chris off the hook for now..
09-20-2005, 10:08 AM
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Re: Load transfer question (RR98ITR)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RR98ITR »</TD></TR><TR><TD CLASS="quote">
Is it like pole vaulting...only around a corner?
</TD></TR></TABLE>
If one side's roll center moves laterally a lot more than the other (which is easy to think about if you got wheel lift), the roll axis pivots to the side so it's partly in the "pitch plane". Any roll motion will be a combined roll and pitch motion. You can use Eulerian/Lagrange dynamics to determine the actual motion in each direction. Now a lateral force at the CG causes lateral and longitudinal load transfers. Though the force is only lateral, the rigid body motions (and force reactions) are dependant on the contraints of the system (wheels on ground) and are transferred into lateral and longitudinal directions.
[Even though I argue that a "roll center" doesn't make sense when you lift a wheel, the vehicle still has a roll axis since it's a rigid body.]
Yeah, it's like pole vaulting around a corner.
Edit: for Tyson
Modified by GSpeedR at 2:19 PM 9/20/2005
Is it like pole vaulting...only around a corner?
</TD></TR></TABLE>
If one side's roll center moves laterally a lot more than the other (which is easy to think about if you got wheel lift), the roll axis pivots to the side so it's partly in the "pitch plane". Any roll motion will be a combined roll and pitch motion. You can use Eulerian/Lagrange dynamics to determine the actual motion in each direction. Now a lateral force at the CG causes lateral and longitudinal load transfers. Though the force is only lateral, the rigid body motions (and force reactions) are dependant on the contraints of the system (wheels on ground) and are transferred into lateral and longitudinal directions.
[Even though I argue that a "roll center" doesn't make sense when you lift a wheel, the vehicle still has a roll axis since it's a rigid body.]
Yeah, it's like pole vaulting around a corner.
Edit: for Tyson
Modified by GSpeedR at 2:19 PM 9/20/2005
09-20-2005, 10:25 AM
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Re: Load transfer question (GSpeedR)
So you're saying the outside rear gets heavier after the inside rear lifts as the remaining lateral forces are generated.
Because the dynamic roll axis (let's just say) runs from the outside rear contact patch to the front roll center which is migrating toward the inside.
It sounds pretty good. It also sounds pretty bad. If true it'd be an argument in favor of a front geometry that minimized lateral migration of the RC (if that matters in the new age) and roll stiffness bias that kept the inside rear in light contact so as to maintain a roll axis (if that has any meaning at all any more) closer to being parallel to the centerline of the car, and "may even raise questions with respect to zero droop which you'd never run on the front of an fwd anyway"...
Interesting - tell us more.
Scott, who still isn't 100% sure this isn't Road Runner Physics...
*Edited to add complexehensity.
Modified by RR98ITR at 11:59 AM 9/20/2005
Because the dynamic roll axis (let's just say) runs from the outside rear contact patch to the front roll center which is migrating toward the inside.
It sounds pretty good. It also sounds pretty bad. If true it'd be an argument in favor of a front geometry that minimized lateral migration of the RC (if that matters in the new age) and roll stiffness bias that kept the inside rear in light contact so as to maintain a roll axis (if that has any meaning at all any more) closer to being parallel to the centerline of the car, and "may even raise questions with respect to zero droop which you'd never run on the front of an fwd anyway"...
Interesting - tell us more.
Scott, who still isn't 100% sure this isn't Road Runner Physics...
*Edited to add complexehensity.
Modified by RR98ITR at 11:59 AM 9/20/2005
09-20-2005, 12:12 PM
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Re: Load transfer question (RR98ITR)
I've been trying to formulate some thought experiments for this, and here's the mess I've made of it...
Imagine a quite large turntable on which a car is parked facing a tangent to the circle. Now imagine that that turntable is rotating at some certain rotational speed and accelerating at a rate slow enough that any particular instant can be viewed as steady-state.
So as the steady state speed of the turntable increases (heh!), the centrifugal force increases (purely a lateral load due to the orientation of the car), and the car starts to lean. Eventually the car starts to lift its inside rear tire. Since we are talking purely about suspension theory, we can ignore the different slip angles of the front and rear tires, scrubbing of speed and all that (that occurs on the racetrack, but not on the turntable), correct?
At the instant before the rear inside tire lifts, we agree that the front/rear weight ratio determines the split of vertical load between the front and rear tire pair?
Now at the instant that inside rear tire starts to lift, some things change. If there is no further transfer of load to the outside rear tire, the suspension (a spring, F=k*x) will not compress any more, right? If so, and the car continues to increase in roll angle, then the center of the rear of the car will start jacking up, no?
(WAY AFTER THE FACT EDIT: The above paragraph about the spring not compressing anymore is wrong. I was not thinking properly about the loading of the spring, thinking the vertical load on the contact patch= load on the spring, which is not the case)
Either the pitch and roll axes are coupled (if those axes are defined by the original contact patches) at that point, or the front also starts equally jacking up. Since I don't see anything on the front end that would cause it to want to jack up yet, I'd expect the case to be the former... but does that mean anything for weight transfer?
Assuming the tires have enough grip and the turntable "steady-state velocity acceleration" (heh!) process continues, eventually the inside front tire also lifts. At this point the car is kinda like a motorcycle, and once again I believe we all agree that the front/rear weight ratio determines the split of the vertical load between the front and the rear, no? Of course, the front of the car has drooped in relation to the rear due to the fact that the front needs more "x" out of F=k*x to get the F it needs, but that shouldn't be of worry, should it?
So, I imagine we agree that there is nothing going on when the car has 4 wheels on the ground in terms of front-rear weight transfer, and there is nothing going on when the car has 2 wheels on the ground. If there is front-rear weight transfer during the 3-wheeling phase, it would be interesting to see what the plots look like in terms of longitudinal weight transfer per degree roll angle.
I have too much of a headache right now (from other things), so I'd appreciate someone shoot holes in whatever parts of the example I've put up so far that they feel are invalid.
blah..
edit: clarification
Modified by MechE00 at 11:01 AM 9/30/2005
Imagine a quite large turntable on which a car is parked facing a tangent to the circle. Now imagine that that turntable is rotating at some certain rotational speed and accelerating at a rate slow enough that any particular instant can be viewed as steady-state.
So as the steady state speed of the turntable increases (heh!), the centrifugal force increases (purely a lateral load due to the orientation of the car), and the car starts to lean. Eventually the car starts to lift its inside rear tire. Since we are talking purely about suspension theory, we can ignore the different slip angles of the front and rear tires, scrubbing of speed and all that (that occurs on the racetrack, but not on the turntable), correct?
At the instant before the rear inside tire lifts, we agree that the front/rear weight ratio determines the split of vertical load between the front and rear tire pair?
Now at the instant that inside rear tire starts to lift, some things change. If there is no further transfer of load to the outside rear tire, the suspension (a spring, F=k*x) will not compress any more, right? If so, and the car continues to increase in roll angle, then the center of the rear of the car will start jacking up, no?
(WAY AFTER THE FACT EDIT: The above paragraph about the spring not compressing anymore is wrong. I was not thinking properly about the loading of the spring, thinking the vertical load on the contact patch= load on the spring, which is not the case)
Either the pitch and roll axes are coupled (if those axes are defined by the original contact patches) at that point, or the front also starts equally jacking up. Since I don't see anything on the front end that would cause it to want to jack up yet, I'd expect the case to be the former... but does that mean anything for weight transfer?
Assuming the tires have enough grip and the turntable "steady-state velocity acceleration" (heh!) process continues, eventually the inside front tire also lifts. At this point the car is kinda like a motorcycle, and once again I believe we all agree that the front/rear weight ratio determines the split of the vertical load between the front and the rear, no? Of course, the front of the car has drooped in relation to the rear due to the fact that the front needs more "x" out of F=k*x to get the F it needs, but that shouldn't be of worry, should it?
So, I imagine we agree that there is nothing going on when the car has 4 wheels on the ground in terms of front-rear weight transfer, and there is nothing going on when the car has 2 wheels on the ground. If there is front-rear weight transfer during the 3-wheeling phase, it would be interesting to see what the plots look like in terms of longitudinal weight transfer per degree roll angle.
I have too much of a headache right now (from other things), so I'd appreciate someone shoot holes in whatever parts of the example I've put up so far that they feel are invalid.
blah..
edit: clarification
Modified by MechE00 at 11:01 AM 9/30/2005