Rear control arm geometry question?

[pdqwagon]

The rear of my car sits very low, my upper control arms are at a bad angle at ride height. I am relocating the front of the upper control arm up 2-3 inches to correct the angle. My question is, would I move the rear of the lower control arm down the same amount to keep the geometry the same or is there a different ratio that I need to know about.

 

[Supe]

Try to keep the lower control arm parallel to the ground.

 

[pdqwagon]

Try to keep the lower control arm parallel to the ground.

But is this always true no matter what angle the upper arms are at? If I move the upper arms up at the front and not move the lower arms the same amount wont my instant center be way off? I guess I should just adjust them both to the correct instant center to start with.

 

[MalibuMan1979]

go to one of our sponsors site. baseline suspensions. read baselining your suspension. really informed me..

 

[LS6 Tommy]

Keep in mind, raising the front mounting point of the upper arms will move the instant center forward & will basically make the front of the car want to rise on launch.

Tommy

 

[el meano]

thats a good thing isnt it??

 

[10secBu]

Have you plotted out the rear 4 link to see where the I/C and anti-squat is?

Why do you want to raise the front upper mount?

Seems backwards to me.

 

[LS6 Tommy]

thats a good thing isnt it??

If you like wheelstands. :lol: Ther's more to hooking the car up than just lifting the front. Antisquat comes into play, too. There's more to it than I really have a lot of background with. Where's Norm when I need him? :lol:

Tommy

 

[tiedyemike8]

But if the instant center is too far back, wouldn't the rear of the car try to jump off the ground at launch, throwing everything out of whack and probably resulting in a lot of wheelspin? Raising the front of the upper arms would move instant center forward again to a better point.
If you are going to relocate any mounting points, I would make several sets of holes on the bracket to work with, and test things out at the track. That way, you can do a bit of tuning to the suspension on the spot.

 

[LS6 Tommy]

But if the instant center is too far back, wouldn't the rear of the car try to jump off the ground at launch, throwing everything out of whack and probably resulting in a lot of wheelspin?

That's Antisquat.
I hope I get this right as I'm mostly going from memory, but here goes [-o<

Depending on the car, you can increase traction by increasing or decreasing antisquat. Too much AS hits the tires really hard, but only on lauch. Then as the suspension sets, the ires may spin. Not enough AS makes the rear droop on launch & unloads the suspension, also causing tire spin right off.

When you raise the front of the top you're increasing the IC, but not correctly. You're moving the IC up above the Center of Gravity, too. This increases Percentage of Rise.You have to move all 4 mounts, top & bottom to increase IC without changing the PR. more PR "hits" the tires harder, less PR hits softer.

I'm sure there's stuff to read & diagrams to help you visualize on the internet, but I don't have time to search here at work.

Tommy