Buggy Suspenion Question

[DEZFAN]

I am currently designing an unequal length a-arm front suspension for a buggy. I was thinking about moving the inner upper arm pivot location down more than outer spindle location. Creating what I guess is refered to as your "swing arm length" . It looks to produce more camber gain from parallel to full bump, and less camber gain from parallel to full droop. This seems handy, but a lot of the buggies out there seem to not use this. What are your opinions?

[ntsqd]

Herb Adams has a fair amount to say about Virtual Swing Arm length in his book. Might look that up and how it fits what you want to do.

[DEZFAN]

Yes, I have his book, and it has a lot of good information. But what I quest is more knowledge on offroad suspensions.

[Scott_F]

You are correct about the camber gain. When your lower arm is parallel to the ground, how much lower is your upper arm pivot compared to the upper ball joint? As your arms go down from this point, the camber goes slightly positive until the upper arm passes horizontal.

[Gordon]

One school of thought is that you want the camber gain in droop as well because it minimizes the scrub as the suspension cycles. if the track width at the contact patch changes as the suspension cycles, the tires have to slide sideways. Of course excesive camber is bad too so it is a balancing act.

[DEZFAN]

Scott, I set the upper inner pivot 1" lower, with 2 degrees of built in camber on the spindle the camber doesn't reach positive when the upper arm is parrallel. At full bump I get -6 degrees and at full droop I get -2 degrees with 25" of travel. Although as Gordon said, scrub is now a problem it shows 3" of scrub movement. What would be a safe number for the scrub distance. If I left the arms parallel I would get -3 degrees at bump and -7 at droop at 25" of travel and my scub is 1.2".

[FABRICATOR]

Spare the scrub and spoil the camber.

[Scott_F]

Like FAB said, spare the tie rod, and spoil the bump steer, or something like that.

Camber gain at bump is what is important. That affects cornering, by keeping the tire flatter to the ground as the body rolls. Camber gain at droop helps minimize the side scrub. Reducing scrub is worthwhile, just not at the expense of the other parameters. If you cycle the suspension while the car is stationary, the tires will slide sideways. When the car is rolling, the scrub is spread out over the time/distance it takes to compress the suspension.

[DEZFAN]

Thanks for the input guys. Although Fabricator stumped me on the spare and spoil?

[FABRICATOR]

Take care of the camber. Side scrub is not very relavent.

[Scott_F]

FAB was paraphrasing an old saying: "spare the rod, spoil the child", which means if you don't spank your kids, they will turn into spoiled brats. The rod would be a switch, whip or belt. Nowadays, spank your kids, go to jail.

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