Visit The Dirt Forum for More Information

Author Topic:   upper control arm length
racing north
Member
posted December 31, 2003 02:59 PM
I just finished tacking in the upper control arm mounts. I placed them as far in as the frame would allow. Looking back at them and with a steering gear in place, I will not be able to put a steering shaft on. So the question is, Is the there any benefit to have the left side shorter than the right? I have to move the left but would be nice only to move have the project. Thanks for the input.


racing north
Member
posted January 01, 2004 01:46 PM
BTT, Come on one of you guys must have played with this before.

AKA SS#4

[This message has been edited by racing north (edited January 01, 2004).]

CUSTOMPERFORMANCE
Member
posted January 01, 2004 10:04 PM
Camber change will be faster on the left with the shorter upper. A book i have says you want to keep your upper a arm length around 60% of the lower.


CUSTOMPERFORMANCE
Member
posted January 01, 2004 10:06 PM
When I do Harris style chevelle stubs with the plate mount for the uppers and mount them at the same angle as the lowers the left upper mount has to be notched for the steering shaft to run through it.


ss#4
Member
posted January 02, 2004 07:46 AM
I am using the adjustable uppers. Inorder to clear the shaft I had to shorten the front arm position by 2 inches. Yes I am trying to keep the upper mounts parrallel to the lowers. Any chance you have any photos looking down how these should look. my email address is reckow.d@duraauto.com
thanks

aka "racingnorth"

racing north
Member
posted January 02, 2004 08:10 PM
I can also be reached at reckow66@hotmail.com.


Elwood
Member
posted January 07, 2004 08:54 AM
Ok I can always come here and find a topic in the same area that I am having trouble with.

2002 Larkins 73-77 chevelle stub. My upper mounts are not parallel. the forward mounts are at about a 45 degree angle to the outside of the car. The rear mounts are I would guess about on a 20-30 degree aimed to the inside of the car.

Now with that being said the rear arm is about 1" longer than the forward arm (5"). Reading the Steve Smith book as a guide line saying that those mounts should be parallel puts me in my pickle. If I were to move the mounts to a parallel angle, I would shorten both arms by about 2". How would this affect the handling and bump steer...etc...

Is that angle critical to the ultimate handling of the car or would it be only a minor improvment. Basically asking should I take the time and effort to change it or leave it as is. Note the car is fast now and handles very well.

Iowamod20
Member
posted January 07, 2004 11:26 AM
Haveing the uppers exactly parallel with the lowers is not absolutely necessary. If you have angle in your lowers, you should have angle in the uppers. If the lowers are parallel with centerline, than run your uppers that way as well, i.e. older ford stubs and latemodels.

If anything, run more angle in the uppers than your lowers. However this is difficult to do, depending on your packaging constraints.

NJantz
Member
posted January 07, 2004 12:14 PM
quote:
Originally posted by racing north:
I just finished tacking in the upper control arm mounts. I placed them as far in as the frame would allow. Looking back at them and with a steering gear in place, I will not be able to put a steering shaft on. So the question is, Is the there any benefit to have the left side shorter than the right? I have to move the left but would be nice only to move have the project. Thanks for the input.

Your left a-arm will have 7deg. more angle in it than your right producing a sharper camber curve. I agree with what Custom said about the length being 60% of what the other arm is. All the books I've read say a motion ratio of .6 or 60% works best. They've tried it all.

I've never heard of anyone doing what you want to do or even read anything. Your roll center will definitely be different. The car will technically have two different roll centers in theory. The left will a little more than 2" higher than the right. I'm not sure how you combine two front roll centers into one??? But I imagine they'll act through a common point.

Your wheel rate on the left side will not be equal to the right side due to the motion ratios being different on both sides. This is not that big of a deal, you'll probably just not run the same spring you used to run there. A softer one will be needed due to a smaller motion ratio.

Wheel Rate = Spring Rate x Motion Ratio

I say give it a try and see what happens you might find the next hot setup.

[This message has been edited by NJantz (edited January 07, 2004).]

[This message has been edited by NJantz (edited January 07, 2004).]

NJantz
Member
posted January 07, 2004 12:24 PM
racing north- did you get my email I sent to you a while back when you were asking about this stuff? I never heard back from you.


NJantz
Member
posted January 08, 2004 02:01 PM
I've figured out where you'll roll center will move to!

Instead of being at the centerline of the car, it will move several inches to the left of centerline.

Think of it as a teeter totter. Instead of the fulcrum (pivot) point being centered, it will move towards the leftside. This will create a longer right side lever arm requiring a stiffer spring than if it was perfectly centered.


Back to the Archives