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2G: Rear camber adjusting (Math guru needed)

2K views 5 replies 4 participants last post by  kronus 
#1 ·
After getting new tires and replacing nearly control arm on the car I decided to take it for an alignment. Took it to a buddy's shop and he got everything within spec pretty easily, except for the rear camber. Factory calls for -.8* to -1.8*, and he got...

LEFT = -.6*
RIGHT = -1.1*

Right now I have the DIY fender washer mod. 4 washers in each with longer bolts. He told me to re-adjust the best I can and take it back and he'll check it out again. My question is this.... Besides trial and error how do I figure out how much to move that upper control arm to get the rear within spec?

I found one math equation online that read as followed...

Tire Diameter(24.875) x Pi(3.14) / 360 = .217" = 1*

Does that seem correct? I also included a quick sketch if it helps at all.
 

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#2 · (Edited)
2 x pi x r = pi x D = circumference of a circle. So in your case, that is:
24.875 x pi . If you divide that by 360, you get the angular length (not sure if that's the correct term) of one degree around your tire. In other words, if you bend a tape measure around your tire, every .217" on the tape is equal to one degree of the circle. I'm not sure how that helps you adjust your camber.

What you need to figure out is how far to push or pull the top of the tire, right? So you're trying to get more negative camber on your left tire, which means you need to pull in the top. If I'm understanding everything, you need to remove washers to do that.

Let's build a triangle. The hypotenuse will be the length of the tire, or 24.875. Take a level and make it plumb to the bottom of the tire. Measure the distance from the floor to the top of the tire and the side of the tire. That's the legs of the triangle.

Plug those numbers into here: http://www.calculatorsoup.com/calculators/geometry-plane/triangle-theorems.php . Change the drop-down to SSS. This will give you the camber angle. Change the calculator to ASA. Use the length of the tire for the side (24.875), 90 for one angle, and calculate your camber angle. This should let you figure out how many washers to take out.

At this point, I've either thoroughly confused you, or you should be able to figure it out from there. Let me know. I'm a little tired and it's a little hard to explain without pictures.
 
#3 ·
I haven't adjusted mine in forever ... long time ago I tried the washer method and could never get it just right ... I finally spent the money on an ingalls kit and haven't had to have it looked at again ... it's probably been close to 7 years. Just a thought.
 
#4 ·
I made some adjustments and Ill be going back tomorrow to see the results. I will post them up.
 
#5 ·
Sorry for the late reply.

So I basically found out that a metric fender washer with a thickness of .098"(2.5mm) will add or subtract ~0.3* rear camber and a standard fender washer with a thickness of .062" will add or subtract ~0.2* rear camber.

After making needed adjustments my rear camber came out to be -1.3* on the left and -1.4* on the right.
 
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