Measuring front suspension geometry

Billy_the_Kid

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I'm trying to plot and graph the front suspension on my CORR Stock Truck ('99 Chevy) but have a small dilema. The upper and lower a-arm chassis points are in stock location, which points them inward on the lower a-arm and outward on the upper a-arm, causing lots of caster gain in full bump. So my question is, when measuring for the location of the inner pivot points or the length of the upper and lower a-arms for front suspension geometry, which point on the chassis do you measure to? the shorter of the two? or the longer of the two? or the average/mean of the two? I've never tried to plot this type of suspension before. All of our circle track stuff had the a-arms in line front to rear. I've read two different methods, #1 measure to the longest point, #2 measure the average distance between the two.

So does anybody know for sure which it is? Thanks for the help.

#817 CORR Stock
 

Billy_the_Kid

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OK. After thinking about it some more I think I kind of answered my own question, but now have another.

Looking at the front suspension from the front, it kind of makes sense to use the inner most pivot point for the lateral location. But now the question is, how do I plot the elevation of that point. With the built in antidive, both the upper and lower chassis points are at different elevations front to rear. So which one of those do I use? higher? lower? average?

#817 CORR Stock
 

FABRICATOR

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IMHO, this cannot be done simply by knowing inner pivot points. It also depends on where the ball joint is on the lateral plane of the control arm. The effective length and pivot point of the control arm is where a line from the ball joint intersects perpendicular with the axis of the control arm.
 

Billy_the_Kid

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I know it can't be done just by knowing the inner pivot points. Finding the location of the ball joints is easy to figure out because there is only one point to measure to, that wasn't my question.

The effective length of a control arm is the length of a line perpendicular to the axis of said arm and ball joint. But I still need to know how to plot the elevation (y) of the inner pivot points? or point?

#817 CORR Stock
 

FABRICATOR

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Perhaps I misunderstood your question. The ball joint location has to do with more than just the effective length of the control arm. lt also will determine the elevation of the control arm pivot point. That intersection should be the elevation of the pivot point.
 

FABRICATOR

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That's just the way I understood it the first time and, and must reiterate the same answer.
 

Billy_the_Kid

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So, basically this is all about locating points of intersection that are perpendicular to the inner pivot point line, right?

To plot the effective inner pivot point in the FRONT VIEW of my diagram, I would have to use the "x" dimension from the perpendicular intersection in the TOP VIEW, and the "y" dimension from the perpendicular intersection in the SIDE VIEW. Is this correct? It makes sense because the "x" dimensions are common between the FRONT and TOP views, and the "y" dimensions are common between the FRONT and SIDE views.

Does this make sense to everyone? Anyone agree/disagree?

Fabricator, thanks for the help. You and I must have been talking/thinking in different languages when I first posted this question. That or I just didn't get it until now.

#817 CORR Stock
 

FABRICATOR

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I think you got it.
 

Billy_the_Kid

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Yeah, I think I just "made the connection". (Mr. Obvious)

But now it seems too simple. If people could see me right now I'm sitting here with two pens taped together in the shape of a T, twirling them around and trying to visualize all of this....
 
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