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 Post Posted: Fri Jul 30, 2010 6:26 pm 
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ky mustang wrote:
Shrinker, I know I said I would back out of this =; , but when you start lengthening your link bars you add leverage as far as the upward lift of the link bar. It gives less weight an advantage over the housing in your hypothetical example. No different than fetching a longer breaker bar out of the tool box to turn a bolt torqued to a certain amount except exactly backwards from where the work is coming from .

Hi ky mustang, the bar has a swivel joint at both ends so it cant supply a bending force all it can do is thrust straight down the bar and Billy has correctly pointed out that a force can be
BillyShope wrote:
placed anywhere along its line of action without changing the effect
. In my hypothetical the bar is just placing the start of that force at the extended end point of the bar. Perhaps I didn't explain myself correctly, its an imaginary car where the top and bottom bar are on there original respective angles going forward from the diff but they are maybe 50" long and mounted to the chassis at their intersection point. It's a ladder bar, I just didn't say it.
BillyShope wrote:
The force acting on a line of action which passes through the rear tire patch and the instant center can be considered to act at any one of the infinite number of points which constitutes the line. So, the vertical and horizontal components of that force can be applied anywhere along that line without effecting a change.
We are obviously starting to reach an impasse with our discussion however consider this, We build a special tool to apply torque to just the axle housing so that we can simulate the torque reaction component and we attach a ladder bar to the axle housing for simplicity. When we apply torque in the direction the axle housing experiences, the ladder bar will lift the body at the front swivel. If we move that front swivel to different places it will lift the body from different places. If the ladder bar is long the lift will be less than if it was short. I don't think anyone will disagree with that. Its a simple torque arm length thing.
So now we cut the ladder bar and convert it into a 4 link and you say the lines of force action intersect and we call that point the IC. Its the same point still as when we had it as a ladder bar with a defined point. Ok, so when we torque the axle housing, forces intersect at the IC and its a lift force to hold the torque, same as with the ladder bar deal. No problem so far. Now we add forward acceleration. The forward acceleration is a constant force that occurs at the IC irrespective of the length of the torque arm used to resist the torque. Lets go back to the ladder bar idea, the front heim gets shoved forward with eg 1000lbs force but its being shoved upward with maybe 500 lbs force due to it length of torque arm. If I move the ladder bar front heim back closer to the diff the lift force to resist the torque gets greater but the forward force due to acceleration is still the same. That means the vector is a different angle and a different force value. The car reacts different.
I will say something else to clear something up as well. The thing that pushes the car forward is the Axle bearing housing. Yes the force is applied at the ground, but the force at the ground reacts into the earths mass, the equal and opposite reaction to that is at the axle centerline. That is why there is a torque reaction at the axle housing. But the forward thrust is a horizontal component at the height of the axle bearing and that height has an effect upon the vector at the IC. So if you put gokart wheels on your car the forward force is only 4" above the ground. If you put monster truck wheels on your car the forward force is way up there. To run gokart wheels or monster truck wheels you would need a different gear ratio in the diff so the torque you have to react against would be different. Even though the forward force and acceleration can be made the same you are going to have a different torque reaction lift force so your going to have a different vector etc.
To place the IC anywhere along this 100% line you would need different 4 link geometry and if you place the IC a long way forward and quite high but still on the line, the link bars will both be pointing up. When you launch that setup the acceleration force will convert both bars into pushing the body up with some force value. So now you have a situation where the forward force is creating antisquat but you have lost the torque antisquat. You could use parallel arms pointing upward to an infinite point on the 100% line, then there would be zero torque lift and only forward acceleration lift.

Basically what I'm getting at is you relate the vector at the IC and how it performs anti-squat to the position of the front axle and I say the reaction that is anti-squat is related to the CG because thats the inertia point. I dont know how to explain my point any other way so if we agree to disagree at this stage once again then so be it. It's fun.


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 Post Posted: Fri Jul 30, 2010 8:29 pm 
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This is a good read!!!!!!

http://afcoracing.com/tech_pages/dragshock.shtml

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 Post Posted: Fri Jul 30, 2010 11:41 pm 
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I have a question for Shrinker. We know we can set an IC, or Ladder bar low enough to create compression in the rear. Where did the lift in these bars go then? It had to be overcome by just front to rear weight transfer. Right?

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 Post Posted: Sat Jul 31, 2010 1:58 am 
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Bubstr wrote:
We know we can set an IC, or Ladder bar low enough to create compression in the rear. Where did the lift in these bars go then? It had to be overcome by just front to rear weight transfer. Right?
Thats partly right. Your on the right track. Its overcome by the CG inertia. Its the CG inertia that compresses the springs. The lower you go with the IC the more the diff 'drives' over the top of it. The acceleration force counteracts the lift force when the IC is below the diff, thats why a low IC squats. When the IC is so low that both bars are pointing downward the forward force component in the bars is dramatically directed downward thus reducing the total upward force, reducing the anti-squat. The angle of the bottom bar is most critical. The bottom bar is the dominant force provider. It's the one with massive force in it, if the bottom bar is angled down the force pushes the body down, thats seen as spring compression.


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 Post Posted: Sat Jul 31, 2010 6:31 am 
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Elkyman wrote:
I have not red anywhere that it can be done any other way.

Here's another way:
http://www.racetec.cc/shope/tim.38.htm

This is a manual version of how it would be done in a CAD program. The accuracy is dependent upon the time you put into it.


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 Post Posted: Sat Jul 31, 2010 3:17 pm 
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Okay, the following images are terrible, but your hands will shake when you're 74, too. I had pretty pictures almost completed in CAD when my software developed a hiccup. So, these will have to do:

Image
Above, we have a nice symmetrical car accelerating, to the right, at 2 Gs. Statically, there were 1500 pounds on the rear tires. An extra 1200 is transferred during acceleration. Note that there is a horizontal force balance and a vertical force balance. There is also a moment balance. If you take the moments about the rear tire patch, with counterclockwise moments positive, 20(6000) + 100(1500) - 100(1200) - 50(3000) = zero.
Image
Above is shrinker's suggestion, with an additional wheelbase length of 500 weightless inches. Initially, there are 2750 pounds on the rear wheels, with an additional 200 pounds added during acceleration. Again, vertical and horizontal forces are balanced. As for the moment balance, 20(6000) + 600(250) - 600(200) - 50(3000) = zero.
Image
This last image shows the forces on the rear axle assembly of the 600 inch wheelbase car during launch. Since the instant center can be located anywhere along the line of constant percent antisquat, I have arbitrarily placed it 40 out and 8 up. For a moment balance, 8(6000) - 40(1200) = zero. The 2750 and 200 pound vertical loads are acting at the tire patch as in the previous picture. The additional 2750 pounds, with opposite sense, represents the static load being carried through the suspension springs.

Now, what about that extra 1000 pounds? Note that it's essential for a vertical force balance, but where does it come from? It comes from the fact that the rear of the car has been elevated, causing a force reversal in the suspension springs.

That force...and the separation involved...can only be eliminated by placing the instant center on the new 100% antisquat line. This line has a slope of 20 divided by 600. This reduces the vertical component from 1200 pounds to 200 and that extra force from the springs is no longer needed.

This is what I've been trying to explain by waving my arms. The pictures, crude as they are, should have cleared the matter up.
http://www.racetec.cc/shope


Last edited by BillyShope on Sun Aug 01, 2010 7:54 am, edited 3 times in total.

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 Post Posted: Sat Jul 31, 2010 4:43 pm 
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shrinker wrote:
Bubstr wrote:
We know we can set an IC, or Ladder bar low enough to create compression in the rear. Where did the lift in these bars go then? It had to be overcome by just front to rear weight transfer. Right?
Thats partly right. Your on the right track. Its overcome by the CG inertia. Its the CG inertia that compresses the springs. The lower you go with the IC the more the diff 'drives' over the top of it. The acceleration force counteracts the lift force when the IC is below the diff, thats why a low IC squats. When the IC is so low that both bars are pointing downward the forward force component in the bars is dramatically directed downward thus reducing the total upward force, reducing the anti-squat. The angle of the bottom bar is most critical. The bottom bar is the dominant force provider. It's the one with massive force in it, if the bottom bar is angled down the force pushes the body down, thats seen as spring compression.



Ok we agree that the force of the Rear directed threw the links is dependent on where the links converge, (the IC). Taking springs and shocks out of the picture, if lower than real Instant center line, it will cause separation. If higher than IC line it will cause Separation.

We could say it is a relationship of the IC to the center of gravity that is important. If we make a neutral line, This would be the balance point of that relationship. As for the rising height of the COG, the forward points of your links rise and your front axle will rise all keeping the same IC neutral line. As for the axle bearings in the rear being the starting point of forward force, the wheel and tire are an extension and you can get no force till you have something to push off of. That is the track. This is the easy part. The hard part is how much weight do you want carried by the links and how much do you want to be carried by the springs and shocks.

In circle track applications, weight carried by your links is called being on the bar, any other weight that would be applied to the contact patch would be carried on the spring. You see a lot of different combination's that work. If they work they are all right. If they don't work they are wrong. The thing is we need to know why. Any thing but physical law will not give us a good picture of how it works. I have like so many made up my own mythical physical laws jut to find flaws in them. Only one set. If you look hard enough, you will find what you know works and why in the real physics. It gives you direction if you need to make changes or experiment.

Billy talks over my head a lot but I know his Physical law and mine are the same. Its a good spot to start looking at what you know works and why.

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 Post Posted: Sat Jul 31, 2010 11:18 pm 
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Bubstr wrote:
We could say it is a relationship of the IC to the center of gravity that is important.

Yes that’s what I'm saying too. If you lifted your car up with a gantry crane hooked to the front crash bar and shoved it up until it balanced itself it would be balancing because of the CG being directly overhead of the center of contact on the ground. If you do that to either car in Billy’s drawing (both have the same CG location ahead of the rear axle) then both cars will balance at the same position. Both cars will have the same body angle etc for the balance point so therefore there is nothing different. If the force that provides acceleration comes from the contact patch then the mass that it pushes is the CG and it doesn’t matter where the front axle is. The balance point is the contact patch to the CG, that’s what matters.
Consider this experiment, you get a pendulum and hang it from the CG.
When you accelerate you move the angle that a pendulum would hang if it was inside the car accelerating with it. If we accelerate the car so that the pendulum points to the rear contact patch it means the car is about to balance all its weight on the rear contact patch. The thing that has caused that is the acceleration upon the CG not the position of the front axle. Not the line of force from the IC, not the 100% anti-squat line, it's just the CG inertia redirecting the CG force to the rear contact patch.

What happens with the IC is it lifts the body, which reduces the weight upon the springs so the springs extend, now the CG is higher than what it would have been without the 4 link lift. You have front to rear transfer due to acceleration etc as well, that compresses the rear springs but the IC lift is always there and it reduces the weight carried by the spring. The weight it reduces is carried by the triangle of the bars directly to the diff. Its not controlled by the shocker, it’s a direct application.
With the raised position of the CG the pendulum doesn’t have to have such a great angle on it to point to the rear patch. That means you reach the balance point at less acceleration. A car with a 4 link can put the front wheels in the air at a lower acceleration rate than one with a solid rear end.
The amount of spring extension measured as linear movement is due to whatever spring rate you have. If you have a 100lb per inch rate spring it will extend 1 inch if you lift 100 lbs off of it. If you have a 200lb spring it will extend 0.5”. The position of the IC in where it’s placed vertically and horizontally in relation to the torque and thrust source (the rear axle) determines how much weight it removes from the springs.

Billy is correct in working all this out as torque moments. He prefers to do it that way; I just break it down to smaller bits that’s all.
The CG creates a moment about the contact patch; the CG creates a moment about the IC. The forward thrust upon the CG creates a moment about the axle centerline. None of those things have anything to do with the position of the front axle and its determination of where this 100% anti-squat geometry point is. The 100% anti-squat position for the IC is not related to the front axle it’s related to where the CG is.

What I disagree with, is the use of the front axle position to determine the correct height of an IC that’s say 50” forward. With 2 cars of identical CG location relative to the rear axle, but with different front axle locations the IC will do identical torque reaction lifting, if it’s in the identical place on both cars.
Both the example cars have a position that the IC should be in to counteract the acceleration weight transfer through the rear springs. If the counter action was perfect the rear springs would not change length under acceleration. If we wanted the body to remain at a constant height we would have to compensate for tire squash so we will need to extend the spring to allow the diff to go down with tire squash and to hold the body stable. The CG is where the inertia force comes from. So the IC point for both example cars to do either of those requirements is the same.
If we draw Billy’s 100% line for both cars, the long wheelbase one will have the 50” forward point for 100% closer to the ground. The 50” forward point is the length of the torque arm it determines the amount of upward force necessary to resist just the torque ft lbs.
If you adjusted the car with the further forward front axle so that its IC was lower but still 50” ahead of the rear axle then its not going to react the same is it. It’s got a different 4 link hasn’t it? All the reactions in a mass come from the inertia of the CG, not from where various parts or limbs of it happen to be. When we use the mass of the body to hold the torque reaction of the diff we use the CG to do it.
Billy has said that you can apply a force anywhere along its line of action and it will be the same. Yes I agree with that, but when you lower the height of the IC on the long wheelbase car you alter the position and vector of the force. If the CG is in the same position to the rear axle on both cars and the force is coming from the rear axle then why do you need to alter the IC just because the wheelbase is longer?
The balance point of the car is no different in the balance test we did at the start with the Gantry crane so the IC doesn’t need to be different either.

What happens in peoples cars is they have different designed 4 links. Some have long bottom bars and short top ones, all sorts of options are used. What happens once the car has force applied and how fast it’s applied and at what thrust value that force is applied and what geometry changes happen to the bars is that you have to tune. Couple that with your choice of springs and shock rates and that’s why everyone has different settings.

I would like to run our car with a higher CG so that I don’t have to use such a short IC but if I lift it 1.5” and move the bars down one set of holes the bars wont be the same length because the holes are not vertically arranged so the reactions across the range of suspension movement (and subsequent geometry changes) will be different. Pinion angle change will differ etc; will it screw the universal joints? There are a lot of questions to solve. I would have to work it all out again and do testing to figure out if raising the car was going to be beneficial. One day I hope to achieve that. Racing is just a series of problems that are patiently waiting to be solved.


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 Post Posted: Sun Aug 01, 2010 2:43 am 
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shrinker wrote:
Bubstr wrote:
We could say it is a relationship of the IC to the center of gravity that is important.

Yes that’s what I'm saying too. If you lifted your car up with a gantry crane hooked to the front crash bar and shoved it up until it balanced itself it would be balancing because of the CG being directly overhead of the center of contact on the ground. If you do that to either car in Billy’s drawing (both have the same CG location ahead of the rear axle) then both cars will balance at the same position. Both cars will have the same body angle etc for the balance point so therefore there is nothing different. If the force that provides acceleration comes from the contact patch then the mass that it pushes is the CG and it doesn’t matter where the front axle is. The balance point is the contact patch to the CG, that’s what matters.
Consider this experiment, you get a pendulum and hang it from the CG.
When you accelerate you move the angle that a pendulum would hang if it was inside the car accelerating with it. If we accelerate the car so that the pendulum points to the rear contact patch it means the car is about to balance all its weight on the rear contact patch. The thing that has caused that is the acceleration upon the CG not the position of the front axle. Not the line of force from the IC, not the 100% anti-squat line, it's just the CG inertia redirecting the CG force to the rear contact patch.

What happens with the IC is it lifts the body, which reduces the weight upon the springs so the springs extend, now the CG is higher than what it would have been without the 4 link lift. You have front to rear transfer due to acceleration etc as well, that compresses the rear springs but the IC lift is always there and it reduces the weight carried by the spring. The weight it reduces is carried by the triangle of the bars directly to the diff. Its not controlled by the shocker, it’s a direct application.
With the raised position of the CG the pendulum doesn’t have to have such a great angle on it to point to the rear patch. That means you reach the balance point at less acceleration. A car with a 4 link can put the front wheels in the air at a lower acceleration rate than one with a solid rear end.
The amount of spring extension measured as linear movement is due to whatever spring rate you have. If you have a 100lb per inch rate spring it will extend 1 inch if you lift 100 lbs off of it. If you have a 200lb spring it will extend 0.5”. The position of the IC in where it’s placed vertically and horizontally in relation to the torque and thrust source (the rear axle) determines how much weight it removes from the springs.

Billy is correct in working all this out as torque moments. He prefers to do it that way; I just break it down to smaller bits that’s all.
The CG creates a moment about the contact patch; the CG creates a moment about the IC. The forward thrust upon the CG creates a moment about the axle centerline. None of those things have anything to do with the position of the front axle and its determination of where this 100% anti-squat geometry point is. The 100% anti-squat position for the IC is not related to the front axle it’s related to where the CG is.

What I disagree with, is the use of the front axle position to determine the correct height of an IC that’s say 50” forward. With 2 cars of identical CG location relative to the rear axle, but with different front axle locations the IC will do identical torque reaction lifting, if it’s in the identical place on both cars.
Both the example cars have a position that the IC should be in to counteract the acceleration weight transfer through the rear springs. If the counter action was perfect the rear springs would not change length under acceleration. If we wanted the body to remain at a constant height we would have to compensate for tire squash so we will need to extend the spring to allow the diff to go down with tire squash and to hold the body stable. The CG is where the inertia force comes from. So the IC point for both example cars to do either of those requirements is the same.
If we draw Billy’s 100% line for both cars, the long wheelbase one will have the 50” forward point for 100% closer to the ground. The 50” forward point is the length of the torque arm it determines the amount of upward force necessary to resist just the torque ft lbs.
If you adjusted the car with the further forward front axle so that its IC was lower but still 50” ahead of the rear axle then its not going to react the same is it. It’s got a different 4 link hasn’t it? All the reactions in a mass come from the inertia of the CG, not from where various parts or limbs of it happen to be. When we use the mass of the body to hold the torque reaction of the diff we use the CG to do it.
Billy has said that you can apply a force anywhere along its line of action and it will be the same. Yes I agree with that, but when you lower the height of the IC on the long wheelbase car you alter the position and vector of the force. If the CG is in the same position to the rear axle on both cars and the force is coming from the rear axle then why do you need to alter the IC just because the wheelbase is longer?
The balance point of the car is no different in the balance test we did at the start with the Gantry crane so the IC doesn’t need to be different either.

What happens in peoples cars is they have different designed 4 links. Some have long bottom bars and short top ones, all sorts of options are used. What happens once the car has force applied and how fast it’s applied and at what thrust value that force is applied and what geometry changes happen to the bars is that you have to tune. Couple that with your choice of springs and shock rates and that’s why everyone has different settings.

I would like to run our car with a higher CG so that I don’t have to use such a short IC but if I lift it 1.5” and move the bars down one set of holes the bars wont be the same length because the holes are not vertically arranged so the reactions across the range of suspension movement (and subsequent geometry changes) will be different. Pinion angle change will differ etc; will it screw the universal joints? There are a lot of questions to solve. I would have to work it all out again and do testing to figure out if raising the car was going to be beneficial. One day I hope to achieve that. Racing is just a series of problems that are patiently waiting to be solved.


Ok If we lifted the car by a crane, anywhere on the car, the only thing we could be certain of is the Center of gravity would fall directly below the attachment point. We wouldn't know how far below, but if we move the lifting spot, we could get real close to pinpointing it by intersecting the angles, It would have nothing to do with any real or spot you want the IC to be, and would prove nothing, because there is no real force lifting the car other than forward force at the rear contact patch. I won't argue there is absolutely no rotational force from the rear axle. First it is not possible to exert any lifting force anywhere other that where there is a mechanical connection. This would be at the forward ends of our links. Although your bottom bar would be pushing and your top bar would seem to be pulling, the overall forward push on both bars pretty much makes this a minimal lift. If it lifts at all, it is at the links front mounting point.

Why it makes sense to me to use the front axle center line at center of gravity height to mark the forward point of the 100% anti squat line is, because that is the forward point that you can get any force input or reaction to the car. The contact patches front and rear are the only place we can get force applied or apply force threw. A car dangling in the air will go nowhere. You have to have a physical connection to apply force. Now on the rear contact patch, your right, It should be below ground level by an inch or so. No one figures that.

Time to look at the force. The rear contact patch is pushing the car directly forward. Can't be pushing up or down because the moment of the tire is on the bottom 90 degrees from horizontal. If we get technical a little is less than and a little is more than, They even out. The COG is higher than the ground and wants to stay right where it is. The old things in motion want to stay in motion and things at rest want to stay at rest thing. The force on the COG is directly rearward. This is a direction that it can not go. It has to rotate on an axis centered at the rear contact patch. This and only this lifts the front. If you have wheelie problems look at these forces to solve your problem. Now the link settings only control the compression or separation in the rear. With a 100% anti squat line, any IC along this line, will be exerting force in the same direction. As if it was right at that forward point above the axle, not having more weight above or below it to cause compression or separation in the rear. Even if we pull a star gazer wheelie The car and all points rotate around that rear contact patch and nothing changes on your IC. If you where lower than 100% to start, you still are, if higher, you still are, and the only thing either will do is determine whether the links move up or down at the forward connecting points. You already have 100% of the weight on the rear, you can't get any more.

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 Post Posted: Sun Aug 01, 2010 6:24 am 
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shrinker wrote:
The 100% anti-squat position for the IC is not related to the front axle it’s related to where the CG is.

I had always heard that a picture is worth a thousand words. Evidently, this is no longer the case.

Shrinker, if your above statement is correct, all you have to do is supply a modification of my free body diagrams (hopefully, with a steadier hand) with the proper application of forces. Remember, there must always be a force and moment balance. It's not a matter of my preference; it's the way physical objects behave.

(If you're wondering what all the editing was about on the previous post: I was trying to replace my crude drawings with CAD pictures. Wasn't able to do it, so you're stuck with the wiggly lines.)
http://www.racetec.cc/shope


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 Post Posted: Sun Aug 01, 2010 9:07 am 
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Bubstr wrote:
Ok If we lifted the car by a crane
My analogy of the crane was to reveal that the CG is the point of balance. I was trying to point out generally throughout the post that when the inertia angle from the CG is at the rear tire patch the car is about to balance on its rear wheels only. I think we are saying the same thing differently.
Bubstr wrote:
It should be below ground level by an inch or so. No one figures that.
Do you care to explain that further?
Bubstr wrote:
The force on the COG is directly rearward. This is a direction that it can not go. It has to rotate on an axis centered at the rear contact patch. This and only this lifts the front.
When you place a car with a 4 link on a chassis dyno it lifts weight off the front springs. Its not going anywhere, its not accelerating so there is another force other than your one that is lifting the front of the car up. Its the torque reaction from the diff lifting the chassis. I have deliberately left out of my comments and my thoughts on where the 4 link forces activate and what values they are etc. That discussion would complicate things beyond belief and is unnecessary. But there is an experiment that I performed that disputes the explanations given in books etc. I do not wish to discuss it presently.
Bubstr wrote:
Even if we pull a star gazer wheelie The car and all points rotate around that rear contact patch and nothing changes on your IC.
"- and nothing changes on your IC-" Maybe your missing something there or didnt fully type out all you wanted to say. The IC changes position lots due to the relative movement from the Diff to the body. Suspension movement alters the 4 link geometry. Any amount of rear spring motion is evidence of 4 link geometry change. If the rear spring compresses or extends then the 4 link has different bar angles relative to the CG so the forces generated are in different directions. Its not a static problem its a dynamic one, the car moves, inertia happens and geometry changes. That change alters the force vector and you haven't got what you started out with.
BillyShope wrote:
Shrinker, if your above statement is correct, all you have to do is supply a modification of my free body diagrams (hopefully, with a steadier hand) with the proper application of forces. Remember, there must always be a force and moment balance. It's not a matter of my preference; it's the way physical objects behave.
I agree with that. My point is that the balance is around the CG not the arbitrary location of the front axle. The 100% point is the relationship of the forces exerted on the front link mounts to the CG not an imaginary point at the front axle.

Thankyou to everyone for their time.


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 Post Posted: Sun Aug 01, 2010 11:43 am 
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shrinker wrote:
I agree with that. My point is that the balance is around the CG not the arbitrary location of the front axle.

The moment balance must be valid about ANY arbitrary point. I chose to take it about the rear tire patch, but I could just as well have taken it about the front tire patch, the center of gravity, or any other point. It must ALWAYS go to null, regardless of the point chosen.

Anyway, I did get the CAD up and running and have included this discussion in another page at my site:
http://www.racetec.cc/shope/tim.48.htm


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 Post Posted: Sun Aug 01, 2010 4:04 pm 
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The thing about an inch or so under ground makes up for tire distortion. While the tire distorts the circular moment of inertia around rear axle does not . the force is still applied at average circumference. This is not that important.

Shrinker wrote ""When you place a car with a 4 link on a chassis dyno it lifts weight off the front springs. Its not going anywhere, its not accelerating so there is another force other than your one that is lifting the front of the car up. Its the torque reaction from the diff lifting the chassis. I have deliberately left out of my comments and my thoughts on where the 4 link forces activate and what values they are etc. That discussion would complicate things beyond belief and is unnecessary. But there is an experiment that I performed that disputes the explanations given in books etc. I do not wish to discuss it presently. ''

When you place any car on a chassis dyno it lifts front. This is just the force pulling the COG reaward. It can not go reaward so it rotates around rear contact patch. This makes the front rise. What the chassis dyno is for, is to replicate forces of acceleration while keeping car stationary. While it can not produce movement forward it will to a degree imput forward force. That is why you chain them.

Bubstr wrote:Even if we pull a star gazer wheelie The car and all points rotate around that rear contact patch and nothing changes on your IC.

"- and nothing changes on your IC-" Maybe your missing something there or didnt fully type out all you wanted to say. The IC changes position lots due to the relative movement from the Diff to the body. Suspension movement alters the 4 link geometry. Any amount of rear spring motion is evidence of 4 link geometry change. If the rear spring compresses or extends then the 4 link has different bar angles relative to the CG so the forces generated are in different directions. Its not a static problem its a dynamic one, the car moves, inertia happens and geometry changes. That change alters the force vector and you haven't got what you started out with.

Ok I should have added,'When you have 100% anti squat with no compression or separation in the rear. If you are inducing squat or separation with your link set up, you don't have to pull the front wheels to change IC. Any ride height change will change IC.

I think we are saying some of the things the same but in different language. Every car that moves has a COG, IC included. Very much more important is they have a balance point of COG Power and Traction. If these are not right the only thing an IC can do is give up traction to compensate. I hate giving anything.

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 Post Posted: Sun Aug 01, 2010 8:21 pm 
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Bubstr wrote:
The thing about an inch or so under ground makes up for tire distortion. While the tire distorts the circular moment of inertia around rear axle does not . the force is still applied at average circumference.
Yes I see how your saying it now. I do the same thing, I just work it out at the new axle height that’s all. What is apparent is that you guys work this out as a series of torque-moments whereas I do it as a series of individual force vectors. I do it that way because it identifies each component and enables breaking everything down into small parts. I have an Excel program I use to do it, it uses circular referencing to arrive at the balance of forces related to engine output. That way I can see what every part of the car is doing and what every point in time is doing. So I can understand if I get a more effective adjustment by going to a spring or shock or bar position etc. Its not a guessing game then its just a math exercise. My program can work it out backwards so that I ask the computer a question and it reveals the options and effectiveness of those options. Its very easy once you learn how to drive it.

Bubstr wrote:
I think we are saying some of the things the same but in different language.
Yes we are, its important to know how to adjust the suspension to effect changes that you understand. As long as we can achieve that understanding then its all OK. There is no doubt (as Berreta will testify =; ) that changing the 4 link results in differences. What is important to factor in is that the 4 link geometry can make the reactions violent or soft. But so can springs and shocks. If you want to get a violent lift at the very first event (hit of the throttle etc) then you need a short IC but if you dont want that effect to overcome everything then you need hard springs. And you use the shocker damping rate to control the time it takes to settle to the balance point of forces. That’s how I look at the problem. You can see that by watching the youtube video I listed earlier. The car does what I describe the four link geometry will do. The Data logger and the Excel program agree with one another. I have explained the reasons why I run the springs and shocks and 4link positions I do. Each car has a way of delivering its power and the job is to harness that.
I have analyzed other cars and they need different settings to match the power delivery technique. What you don’t see by only thinking about this 100% line is the interactions of the dynamics of torque application severity and how it relates to the inertia of the car. But as long as we all can tune to our satisfaction then what ever method we choose is valid.


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 Post Posted: Sun Aug 01, 2010 9:44 pm 
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shrinker wrote:
But as long as we all can tune to our satisfaction then what ever method we choose is valid.


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