Rear suspension set up

[jpwalt1987]

I was looking at baseline suspensions website and their IC calculator the other day and did some measuring on my car. The one thing I didn't understand was the projected length of the control arms. How is that determined? I measured what I could but I don't have access to scales. The car doesn't hook up. Here are the dimensions I came up with.

Lower control arm.
Front bolt 10.25
Rear bolt 9.5

Upper control arm.
Front bolt 19
Rear bolt 18.375

These measurements are from the ground up to the center of the bolt. The car weighs 3680 with me in it. I have UMI control arms. The uppers are double adjustable. The coil springs are Kirbans variable rate springs, about 10 years old. Any advice or suggestions are welcome. Thanks, Jeremy

 

[TRICKSIXPA]

It's best to check the angle. Go to the hardware store and get a magnetic degree finder. Your car on a level surface put it on the flat area on the differential and check it on the drivershaft. Should be about 3 degrees. What are you using for rear sway bar, shocks and tires???

 

[jpwalt1987]

It's best to check the angle. Go to the hardware store and get a magnetic degree finder. Your car on a level surface put it on the flat area on the differential and check it on the drivershaft. Should be about 3 degrees. What are you using for rear sway bar, shocks and tires???

I am not talking about pinion angle. I am referring to the Instant Center location that is determined by the position of the control arms and where they theoretically intersect. I have the stock sway bar and some old Gabriel pro Ryder shocks along with 275/60 MT drag radials. I had some airbags but the developed some leaks. Even at about 45-50 they go up in smoke. I know the track is where I need to test at but I can't ever seem to make it there.

 

[83hurstguy]

When I did mine, I taped a big piece of construction paper to the floor, and used a plumb bob to drop the points down to the ground and marked with a sharpie. From there you can find centerline of the car drawing on the paper, and project your side view lengths. Looks like my car is sitting a bit lower than yours, so the heights won't impact you, but here's what I used as input. Edit: I have Currectrac lowers, and UMI adjustable uppers, so that may impact the projected lengths as well.

Projected LCA length = 18.25" (another G-body suspension guru had 18" on his calculator so I feel close enough)
Projected UCA length = 7.875"
FUCA height: 16" RUCA Height: 17.25"
FLCA height: 8.375" RLCA Height: 8.5"

My rear suspension isn't bad on paper (76% A-S), but due to the Eibach springs and shocks set for handling, I don't get nearly enough weight transfer to get the car to hook. I'm planning to put on the LCA relocation brackets to drop the lower arm 2" and see what the increased A-S does. It puts me up into the 144% A-S range, which is probably a bit excessive, but it's an easy change to go back to stock LCA position for autocrossing if I prefer it (though the LCA brackets do help roll steer as well). The baseline suspensions kit would have raised my A-S significantly (plugging in estimated numbers for how much the UCA angle would change), and I'd have a really short SVSA length, which wouldn't be good for getting on the brakes hard autocrossing.

Probably more information than you wanted... good luck with your project.

 

[jpwalt1987]

Probably more information than you wanted... good luck with your project.

That's exactly what I was looking for!!! But where did you get the projected length? Isn't that supposed to include the imaginary length until the upper and lower controls arms intersect?

 

[83hurstguy]

The projected length is just the length of the control arms as viewed from the side of the car.

For example, if you drop the points onto the ground from a top view, the lower arms are angled towards the front center of the car, and from a side view of the car they angle up or down depending on ride height. Ignore the angles. Side view projected length is simply the longitudinal distance between the front mount point and rear mount point on a plane parallel to the ground.

The imaginary length of the rear suspension instant center (SVSA - side view swing arm) is calculated by the software after you put in the points.

 

[jpwalt1987]

Gotcha!! So the control arm actual length minus the distance it moves towards the center of the car is the projected length. The projected length will be shorted than actual length because they are at an angle. The uppers being at a greater angle towards the center of the car than the lowers. I understand the use of the cardboard and plumb bob now. Thanks.

 

[83hurstguy]

Pretty much. It's really the pythagorean theorem relationship... length of the control arm is the hypotenuse of the triangle, the projected length is one of the triangle legs (so it's not directly additive), and the distance to the center of the car is the other leg of the right triangle.

 

[KEVINS]

The baseline suspensions kit would have raised my A-S significantly (plugging in estimated numbers for how much the UCA angle would change), and I'd have a really short SVSA length, which wouldn't be good for getting on the brakes hard autocrossing.

Hey Luke,
You won't be able to calculate what the geometry "would be" on a Gbody using those calculators so that AS value that you think you would get with the Buckets is not correct. That "would be" calculator was designed for the Ford suspension package only. There is a general calc. for stock suspension cars that will give you what your current geometry looks like but that's it.

Gotcha!! So the control arm actual length minus the distance it moves towards the center of the car is the projected length. The projected length will be shorted than actual length because they are at an angle. The uppers being at a greater angle towards the center of the car than the lowers. I understand the use of the cardboard and plumb bob now. Thanks.

Yep, that's correct. You do not use the actual length of the control arms b/c they are at an angle pointing outward. The length that is used will be shorter than the actual length.

Kevin

 

[83hurstguy]

Hey Luke,
You won't be able to calculate what the geometry "would be" on a Gbody using those calculators so that AS value that you think you would get with the Buckets is not correct. That "would be" calculator was designed for the Ford suspension package only. There is a general calc. for stock suspension cars that will give you what your current geometry looks like but that's it.

Kevin

Kevin, I figured that out after a few data runs on your site, so we ran mine through a separate spreadsheet that a G-body suspension guru made for his own car (I played with moving the mounting point down about 1.5" and back about 1.5" guessing off your pictures). Unfortunately, the shorter UCA length made the angle change occur a lot faster that I wanted it to for handling purposes. I should have quantified "significantly" above... if I remember correctly (did this 3-4 months ago), your kit had the A-S value within 10% of where I would end up with the 2" LCA drop using the relocation values I showed above, so it wasn't a huge increase. It was a good targeted value, especially for drag racing... sorry if my verbiage misconstrued that above. You have a nice product out there, and if I was dedicated straight line I'd definitely consider it. One general comment (if you don't mind me providing feedback) is that it would be nice to have an option for a UCA without a rod end, utilizing a swivel joint or something similar for use on the street. I had rod ends previously, they worked great for about 2k miles (though they do transmit a fair amount of noise into the chassis), then started buzzing.

 

[KEVINS]

Kevin, I figured that out after a few data runs on your site, so we ran mine through a separate spreadsheet that a G-body suspension guru made for his own car (I played with moving the mounting point down about 1.5" and back about 1.5" guessing off your pictures). Unfortunately, the shorter UCA length made the angle change occur a lot faster that I wanted it to for handling purposes. I should have quantified "significantly" above... if I remember correctly (did this 3-4 months ago), your kit had the A-S value within 10% of where I would end up with the 2" LCA drop using the relocation values I showed above, so it wasn't a huge increase. It was a good targeted value, especially for drag racing... sorry if my verbiage misconstrued that above. You have a nice product out there, and if I was dedicated straight line I'd definitely consider it. One general comment (if you don't mind me providing feedback) is that it would be nice to have an option for a UCA without a rod end, utilizing a swivel joint or something similar for use on the street. I had rod ends previously, they worked great for about 2k miles (though they do transmit a fair amount of noise into the chassis), then started buzzing.

That's good and it's clear that you know what you're needing to do. I was worried that the numbers you were coming up with would lead you in the wrong direction that could really mess things up for ya..

You did mention that:
"your kit had the A-S value within 10% of where I would end up with the 2" LCA drop using the relocation values I showed above, so it wasn't a huge increase."
Keep in mind that just b/c the AS values are simliar that the suspension in each of these two sceneros will act totally different b/c the control arm angles push/pull on the chassis at different angles. A 2" drop on the rear LCA will really cause the chassis to react differently dynamically than if it was parallel or ??. So if anyone is reading this, a note to ones self is: do not just go off of the AS values. The actual control arm angles can be more/equally important.

I love feed back.. I personally do not like rod ends for street use b/c poly bushings can run really hard. I have a bucket kit on my car but I modified a Mustang poly bushing to use instead of the rod ends on the chassis side. I don't sell much to the Buick crowd b/c most don't push the suspension hard compared to the Mustang crowd but if there was enough interest and there was a better way to do a quieter bushing combo I'd consider it. If you have an idea PM me!

KS

 

[83hurstguy]

You did mention that:
"your kit had the A-S value within 10% of where I would end up with the 2" LCA drop using the relocation values I showed above, so it wasn't a huge increase."
Keep in mind that just b/c the AS values are simliar that the suspension in each of these two sceneros will act totally different b/c the control arm angles push/pull on the chassis at different angles. A 2" drop on the rear LCA will really cause the chassis to react differently dynamically than if it was parallel or ??. So if anyone is reading this, a note to ones self is: do not just go off of the AS values. The actual control arm angles can be more/equally important.

I love feed back.. I personally do not like rod ends for street use b/c poly bushings can run really hard. I have a bucket kit on my car but I modified a Mustang poly bushing to use instead of the rod ends on the chassis side. I don't sell much to the Buick crowd b/c most don't push the suspension hard compared to the Mustang crowd but if there was enough interest and there was a better way to do a quieter bushing combo I'd consider it. If you have an idea PM me!

KS

I agree with your first paragraph. Keeping the LCA's parallel to ground is a better way to go in many situations.

Is there any chance you use the same thread as UMI/Spohn/Currie and could put a roto-joint/johnny joint type bushing on the end? You'd get the poly isolation with rod end rotation benefits.

 

[KEVINS]

I agree with your first paragraph. Keeping the LCA's parallel to ground is a better way to go in many situations.

Is there any chance you use the same thread as UMI/Spohn/Currie and could put a roto-joint/johnny joint type bushing on the end? You'd get the poly isolation with rod end rotation benefits.

I don't know what thread they use but I've always been skeptical of those joints in being quieter b/c I think they still use a sherical type bearing which is still metal against metal and I can't believe this would isolate much noise at all.

ks

 

[83hurstguy]

I have them on mine, uppers and lowers frame side. Really quiet. They aren't metal to metal... it's a polyurethane race with the ball in the middle. UMI uses delrin races instead, which I have on the uppers, but they are quieter than my rod ends were.

 

[Black Air]

That's good and it's clear that you know what you're needing to do. I was worried that the numbers you were coming up with would lead you in the wrong direction that could really mess things up for ya..

You did mention that:
"your kit had the A-S value within 10% of where I would end up with the 2" LCA drop using the relocation values I showed above, so it wasn't a huge increase."
Keep in mind that just b/c the AS values are simliar that the suspension in each of these two sceneros will act totally different b/c the control arm angles push/pull on the chassis at different angles. A 2" drop on the rear LCA will really cause the chassis to react differently dynamically than if it was parallel or ??. So if anyone is reading this, a note to ones self is: do not just go off of the AS values. The actual control arm angles can be more/equally important.

I love feed back.. I personally do not like rod ends for street use b/c poly bushings can run really hard. I have a bucket kit on my car but I modified a Mustang poly bushing to use instead of the rod ends on the chassis side. I don't sell much to the Buick crowd b/c most don't push the suspension hard compared to the Mustang crowd but if there was enough interest and there was a better way to do a quieter bushing combo I'd consider it. If you have an idea PM me!

KS

Hi Kevin,

I hope I didn't make a big mistake here but I recently bought your Pro gold kit UCA for the Buick GN.
The reason I say this is I already have LCA from Metco with their 2 inch drop brackets in the rear and just noticed it tonight that the brackets were not factory. I noticed they were "welded" in place. And wonder where my AS value will be now, yikes! Is there a way to still make this work in my favor? I have the front UCA in the top position. I'm thinking it will load and unload quickly ..... =(
I also didn't know that these would be noisy =(

 

[KEVINS]

Those dropdown brackets may not be good.
Take some measurements and I'll plot the geometry out and see what it will look like but as you may know these UCA kits are designed to have the LCA's
horizontal with the ground.

Measure from the ground to the axle centerline.
Measure from the ground to the front and rear bolts on the Metco LCA's.
Measure from the ground to the LCA factory mounting hole on the rearend.
Unfortunately any kit that uses rodends will be noisy. It's difficult to design suspension kits that can handle a lot of power and be really quiet. I have the same issues on my GN..


KS