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Old 10-18-2005, 04:24 PM   #41
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Kp you are correct on the binding issue. This is the reason that I use a adjuster top and bottom. As long as you turn both top and bottom any time you adjust the bolt centerline stays the same.

I agree J-Rod. What I was saying is if the car is correct in the rear suspension then the car will not squat from a 4 link adjustment. If you watch a Prostock car leave you will see the rear looks like it is coming down. Actually the tire is being slammed into the pavement and the body is kept from separating from the rearend with the shocks.
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Old 10-18-2005, 05:30 PM   #42
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aha, so now I see why adjustable drag shocks become important, to tune the "planting" impact of the rear and adjust how quickly the suspension reacts, I believe

Thanks J Rod for all the excellent info. I have been looking for some good theory stuff like that.
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Old 10-18-2005, 05:43 PM   #43
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Well I learned just about everything about rear suspension from reading stuff in this thread. Very informative!
I was one of the people who thought it was good for the rear to squat a little on launch (for weight transfer), but although this may transfer a little weight it is horrible for traction, which was my problem. I now understand how the goal is to actually push the rear down away from the body on the launch.

I also realized how much my bad LCA angle is affecting my launch, and Im going to definitely get relocation brackets asap.
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Old 10-18-2005, 07:36 PM   #44
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Just wanted to add this, I read that with a M6 car, the car will "hit" the tires fairly hard on the launch when you drop the clutch and when you shift, while an auto will not hit as hard. I guess this means when setting up for how much "planting" you want the rear suspension to do, manual cars will need less than autos.

this was in http://www.baselinesuspensions.com/i...A_Drag_Car.htm
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Old 10-22-2005, 04:14 PM   #45
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Here's a stupid question, say you where to "do away" with shocks and spings and went with coilovers instead how would this affect you I/C?

Also what would be the optimal angle for the coilovers to be mounted? Or does the angle in which the coilovers are mounted really matter?
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Old 10-22-2005, 06:14 PM   #46
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Quote:
Originally Posted by MADMAN
I have been asked about what instant center is so here we go.

The instant center of a T/A car is the line you draw from the lower control arm mounting point on the housing through the front mounting point of the lcas. Then draw a line down the center of your T/A from the rearend to the front of the car. Where these lines cross is your instant center.

No offense, but in a stock Camaro rear suspension with a fore/aft sliding front mount of the torque arm, the side view IC is a little different and is found as follows:

Extend a line from the rear pivot of the lower control arm (LCA)thru the front pivot forward past the transmission mount. Next a line is drawn perpendicular to the front end of the torque beam where it is attached at its rubber slider joint. This is basically a vertical line with the car at normal ride height. Where this vertical line crosses the line of the lower control arms is the side view Instant Center.

This is quoted from Terry Satchell, a GM suspension engineer very familiar with this subject.

Here's the diagram from the textbook:

http://www.jonaadland.com/Ta.jpg

Note that you can easily raise the IC by dropping the rear pivot height of the LCA. Note also that different ride heights (lowered or raised car) change the IC height. Note that lowering the rear drops the IC, and therefore reduces the anti-squat unless LCA pivots are relocated.

My thanks to Jon Aadland for the picture.

Last edited by Old SStroker; 10-22-2005 at 06:33 PM.
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Old 10-23-2005, 08:53 PM   #47
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So what happens if you rigged mount the front of the torque arm? What is the correct lower control arm angle?
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Old 10-24-2005, 07:12 AM   #48
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Quote:
Originally Posted by GIZMO
So what happens if you rigged mount the front of the torque arm? What is the correct lower control arm angle?
On the Camaro if you put a rigid mount on the front of the torque arm the suspension would try to bind up. It wouldn't become a "3-link" because the rear of the torque arm doesn't pivot.

The "correct" lower control arm (LCA) angle depends on what you want. LCA angle also determines rear roll steer, so if you change the angle very much you change the car's handling. If the arms angle up at the front you tend toward more roll oversteer (loose" in NASCAR-speak) which isn't a very good idea. Angling up a the front raises the IC and antisquat so it generally helps "forward bite", but at the expense of roll oversteer. Every suspension is a compromise.
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Old 10-29-2005, 06:35 PM   #49
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Quote:
Originally Posted by ibgoatin
Here's a stupid question, say you where to "do away" with shocks and spings and went with coilovers instead how would this affect you I/C?

Also what would be the optimal angle for the coilovers to be mounted? Or does the angle in which the coilovers are mounted really matter?
There's no such thing as a stupid question..if you don't know the answer.

Spring and shock location doesn't have any effect on the location of the IC, but ride height (how high the rear of the car sits) does, so if you adjusted the coilovers to raise the rear it would raise the IC.

If you angled the top (chassis) mounts of the coilovers toward or away from the center of the car it would decrease the spring rate or "soften" the spring. Same thing is you angled them fore or aft.

I'd mount the coilovers as nearly upright as practical and choose springs based on the axle mounting position and angle to get the spring rate at the wheel that I wanted.
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Old 06-07-2008, 09:58 AM   #50
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Back from the dead if you guys don't mind. This is the hardest and most important thing for an amateur drag racer to get his arms around.
According to the Jon Aadland drawing, the vertical ic line is drawn perpendicular to the torque arm through the front mount. So, if my premise is correct, raising and lowering the torque arm front mount (not moving it forward or back) simply changes the angle of the ic line (since the T/A is no longer parrallel to the ground and the ic line stays perpendicular to the T/A).

So if the above is correct and my lca line intersects the ic line higher than the t/a mount because of my relo brackets and I then raise the t/a mount, I've moved my ic back and slightly lower.
And if I moved my lca rear mount up so their c/l intersects the ic line below the t/a mount then raising the front t/a mount would move my ic forward.

Is that right?

Wat the hell would THAT do to my launch? joking
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Old 06-07-2008, 12:47 PM   #51
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Quote:
Originally Posted by troopercar View Post
Back from the dead if you guys don't mind. This is the hardest and most important thing for an amateur drag racer to get his arms around.
According to the Jon Aadland drawing, the vertical ic line is drawn perpendicular to the torque arm through the front mount. So, if my premise is correct, raising and lowering the torque arm front mount (not moving it forward or back) simply changes the angle of the ic line (since the T/A is no longer parrallel to the ground and the ic line stays perpendicular to the T/A).

So if the above is correct and my lca line intersects the ic line higher than the t/a mount because of my relo brackets and I then raise the t/a mount, I've moved my ic back and slightly lower.

And if I moved my lca rear mount up so their c/l intersects the ic line below the t/a mount then raising the front t/a mount would move my ic forward.

Is that right?

Wat the hell would THAT do to my launch? joking
I don't think you can physically get the extended LCA centerline to intersect above the TA front mount. My look at the geometry of the raised TA mount and relocation of the LCA mount at the axle raises the IC, with the majority of the change due to the relo brackets.

If you mean relocating the LCA axle mount higher that would be physically difficult and counter productive. It would drop the IC and decrease anti-squat. If you mean raising the chassis mount at the front of the LCA, this would be nearly impossible without butchering the floorpan in the area of the mount.

If you succeed in moving the IC forward without simultaneously raising it you decrease anti-squat, which isn't going to help your launch. That's the reason shorter TAs increase anti-squat...but that's another topic.

Last edited by Old SStroker; 06-07-2008 at 01:11 PM. Reason: Correct my thinking!
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Old 06-07-2008, 12:57 PM   #52
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No I wouldn't raise the lca axle mount any higher than stock, in fact my relo brackets have them quite a bit lower which dramatically increased anti-squat.
The question was am I understanding the way it works correctly? If so, then I am on the path to getting it adjusted properly.
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Old 06-07-2008, 01:06 PM   #53
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And by nature the instant center should be higher with the longer stock-length arm and lower with the shorter torque arms, right? Because farther out the ic vertical line has a better chance of being intersected high by the upward tilted lcas.

I think I got it, but am asking more than saying.
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Old 06-07-2008, 01:23 PM   #54
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Quote:
Originally Posted by troopercar View Post
And by nature the instant center should be higher with the longer stock-length arm and lower with the shorter torque arms, right? Because farther out the ic vertical line has a better chance of being intersected high by the upward tilted lcas.

I think I got it, but am asking more than saying.
http://www.jonaadland.com/Ta.jpg

Draw a line from the center of the rear tire contact patch thru the IC in the side view shown in the link. The steeper the line the higher the anti-squat (AS) percent. You can see that you could have lots of IC locations along a given line. All would have the same AS percentage.

There is no free lunch. You can get into axle hop with too short of a "svsa" (Side View Swing Arm) length.
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Old 06-07-2008, 08:16 PM   #55
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I went to the garage and took some rough, quick measurements. They are not exact, but they are very close. The Aadland drawing is accurate but not to scale so you can't go by that. It shows the LCA being half the length of the T/A. Only on a short, tunnel mount arm, maybe. My stock length is about 54"+/-. My LCA is 19" bolt to bolt.
I made a drawing which is closer to scale (still wouldn't draw hard conclusions from it, just easier to visualize) and based on the actual measurements of the car.
I held a broomstick parrallel (with my finely calibrated eye) to my LCA and it extended way up the door above the T/A mount. hmmm My wife said it was too stupid to take a picture of or I would show you.

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Old 06-07-2008, 08:29 PM   #56
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The drawings in post #32 show the ic being the intersection of the upper and lower arms. If the arms are parrallel, is there no ic? Aadlands drawing shows it being the intersection of the LCA with a perpendicular line through the front T/A mount. Is that the difference between a torque arm and ladder bar setup? Or is someone wrong?
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Old 11-21-2010, 03:15 PM   #57
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Back from the dead. From what I've mesured the IC is the height that the lines from the rear control arms intersect the line dropped down from the torque arm. The torqure arm and the rear control arm lines won't intersect. They will run parallel to each other. So if the rear arms point down the IC will be some where below grade level. This is good for road racing. With LCA relocation brackets the IC will be some where along the door sill height. This can be changed by raising the LCA's or adjusting the height of the front TA mount.
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Old 11-22-2010, 02:57 PM   #58
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If the IC is in front of the CG then the front will tend to rise up. If the IC is behind the CG the rear will rise up. Can some one explain the PR (percentage of rise). When you draw the line from the tire contact point where does it intersect?
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Old 11-22-2010, 03:30 PM   #59
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Hi, 1lejohn..
Your line will travel from the tire contact point hrough the instant center point, and the percentage of rise is determined by the point at which this line intersects a vertical line you need to plot out.... this line is defined by the calculated (theoretical) center of gravity. Front to rear weight bias determines the CG's fore/aft position, and the roll center defines the height of the CG. Since roll center is very difficult to obtain, use the camshaft height as the CG height. Draw a line straight down from the newly plotted CG, and stop at the ground. For percentage of rise, find the intersection of the two lines you've drawn. Where this intersection is on your vertical line defines percentage of rise. The ground is 0%, the CG is 100% Having fun yet?
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Old 11-22-2010, 04:01 PM   #60
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Quote:
Originally Posted by aeicoo View Post
Hi, 1lejohn..
Your line will travel from the tire contact point hrough the instant center point, and the percentage of rise is determined by the point at which this line intersects a vertical line you need to plot out.... this line is defined by the calculated (theoretical) center of gravity. Front to rear weight bias determines the CG's fore/aft position, and the roll center defines the height of the CG. Since roll center is very difficult to obtain, use the camshaft height as the CG height. Draw a line straight down from the newly plotted CG, and stop at the ground. For percentage of rise, find the intersection of the two lines you've drawn. Where this intersection is on your vertical line defines percentage of rise. The ground is 0%, the CG is 100% Having fun yet?


Thank Goodness I have you on my team...All i have to do is drive, haahahaha.
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