I Beam bump steer..

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Staff member
Sep 26, 2014
new zealand
not too sure how many of you saw this one, i suspect you clever ones will know this ,, so here goes..

Ever wonder why you hot rod goes right when you hit a bump? Ever wonder why it feels nervous as it goes down the road?
Spend some time looking at this, and all will be revealed!

For those of us running side steer and hairpins or split wishbones, this is how correct steering geometry looks. Notice that with the Pitman arm pointed down, and in line with the Heim or tie rod end that the wishbone or hairpin hinges on, that the arc of the suspension's up and down movement, closely matches the drag link's arc during it's up and down movement.

That area, where the arcs are right on top of each other, from suspension ride height to 2" compressed, and say 2" rebounded, is EXACTLY where it should be! When the arcs are right on top of each other, there is no difference to move the steering arm on the spindle fore or aft, which is by it's very definition, "bump steer".

If you are wondering about your current set up, here's the way to learn what's up.

First go out to Costco, and grab a sheet of the cardboard they use between the courses on the pallets of toilet paper! The best pattern and "workin' it out paper ever, and they throw away tons each day.

Next, measure how long the wishbones or hair pins are, from the perch pin, to the Heim or tie rod end. Next, measure how long your drag link is, and how far down your pitman arm hangs. Convert these measurements into 1/4" scale, by turning the 1"measurements into 1/4" measurements, and draw the whole thing on your sheet from Costco. Once you've done that,plot the arc the drag link makes, and the arc the suspension makes, and see how close they come to laying over the top of each other. If they don't match fairly well, you just found the reason for the car darting left when you hit a bump! Or, turning right when the suspension unloads!

See? Geometry doesn't have to be dry and boring, when there is a reason to figure it out!


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*Go VW beam...
Dr. Porsche designs can run the baja with tortion bars jiggleing
like topless dancers hanging off a pole!

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