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Author Topic:   which upper A-arms
ss#4
Member
posted November 19, 2003 08:12 AM
I am setting up my small metric chassis to use Nova lowers. Which Afco tubular A-arms should I use? Or what is the best way to measure for them?

Thanks

KnightRider6
Member
posted November 20, 2003 06:19 AM
TTT


NJantz
Member
posted November 20, 2003 08:31 AM
Njantz, thanks for the reply. I have the distance of the Nova lower from front frame mount to ball joint, but I don't have a set of metrics to measure. On the upper I have always understood that the upper mounts should be parallel to the lowers. Is this correct? Aligning them reduces the camber change curve.

What would be the "correct" upper arm if I were using metric lowers and still aligning the mounting points?

mod2ace
Member
posted November 20, 2003 02:30 PM
What year metric frame are you using?
What year nove lowers fit that frame?


ss#4
Member
posted November 20, 2003 02:55 PM
82 malibu small metric
Lowers early Nova with modifications

[This message has been edited by ss#4 (edited November 20, 2003).]

NJantz
Member
posted November 25, 2003 07:30 AM
"On the upper I have always understood that the upper mounts should be parallel to the lowers. Is this correct?"
.... I'm not sure if you are referring to "mounts" or arms. If you are referring to arms, then you want some angle on your upper a arm. Meaning you want the upper
a-arm angling downward to the center of the car. This is so you can get your roll center where it needs to be (around 4") If you ran the upper parallel to the lower, your roll center is at infinity. Infinity means the lines you project off your arms will intersect out in space some where but never in the real world. The more downward angle you put on the upper a-arm, the higher you put the roll center on the front end.

"Aligning them reduces the camber change curve." .....This is basically true, if a-arms are more parallel at static ride height, the wheel stays closer to the static camber during a minimal amount of compression and extension.

What would be the "correct" upper arm if I were using metric lowers and still aligning the mounting points?....This depends on where your upper a-arm mounting mounts are located off the centerline of the car. My upper a-arms on my Metric modified are 7.5"

The best way to figure all of this out is to take all the physical measurements of the parts involved and model them in a CAD software. You can model different lengths on the computer screen then you know exactly what you should do and you'll know what the results will be as far as roll center and camber curves go.

Some alternatives are to purchase some of the suspension analysis software out there. You basially input the dimensions the program asks for and it spits you out the important info.

A third alternative is to buy yourself some poster board and duplicate the linkage so you can see first hand what is going on as the wheel travels up and down.




NJantz
Member
posted November 25, 2003 07:41 AM
SS#4- Can I ask what is the reason you are wanting to change your front end in the first place? Are you wanting a different track width, camber curve, or different roll center? Or all of this?

I have my metric a-arms off the car currently, because I am making some roll center height changes so I'll take a picture and dimension it and send it to you. Feel free to call me.

-Nate



NJantz
Member
posted November 25, 2003 10:16 AM
I figured out a way to make the file into a jpeg.

Note, this sketch was not based on actual values, just approximations, but it still illustrates the point with going from a stock metric configuration to the Nova setup.

TOP PICTURE
The top view illustrates the travel path of the typical metric front suspension. The yellow line indicates the lower control arm, the yellow circle indicates the path that the lower ball joint will travel. The red line illustrates the upper control arm, and the red circle illustrates the path of the upper ball joint. The white lines illustrate the spindle.

The top short arm, long arm configuration allows the camber to remain pretty consistent during the first few inches of compression and rebound. As you get much past 2.5” of compression, positive camber develops.

BOTTOM PICTURE

The line colors represent the same things as the top picture. Except this view shows what would happen if you installed the longer Nova control arm without lengthening the upper a-arm. You’d have too much negative camber at the static ride height. Through out the travel path, it would stay pretty much negative.

CONCLUSION

[This message has been edited by NJantz (edited November 25, 2003).]

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