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04-02-2008, 09:41 AM

#21

hustler

Tour de Franzia

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I looked in the audi trailer at ALMS a decade ago and saw them aligning an r8 on a rack in the trailer. I need a $50k alignment rack on a trailer.

04-08-2008, 03:01 AM

#22

grippgoat

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Quote:

Originally Posted by grippgoat

I thought of a way to measure camber that's indifferent to floor level-ness, as long as the floor is flat. Level floor doesn't really make a difference for toe, I don't think, unless it's way, way off.

Anyway, get a framing square (I think that's what it's called). Long leg needs to reach from the floor to the top of your rim. Set the short leg on the floor, pointing away from the tire. The long leg should now be perpendicular to the floor. Then measure to the bottom of your rim lip to the square, shooting for something fairly close, but not touching the tire, like maybe 1 inch. Call this B. Then do the same to the top lip of your rim, and call this T. Then, measure the vertical distance between the two points you measured, and call this D. Now just do some trig:

camber = DEGREES( ASIN( (T-B)/D ) )

For example, if B is 1.0" and T is 1.5", and D is 16", then camber is 1.79 degrees (well, it's negative, but you know that because the tire is tilted in). Given desired camber, and constant B and D measurements, you can even solve for the T measurement.

T = D * SIN(RADIANS(camber)) + B

So if you wanted 3 degrees, you'd get
1.837 = 16 * SIN(RADIANTS(3.0)) + 1

I'm too lazy to actually try it (Firestone lifetime alignment), but I tested the measurement technique after getting an alignment, and the numbers came out right. It may not be perfect, but it should be able to get you within a tenth or two of a degree.

Also note that if your tires are hella stretched so that you can butt the square right up against the rim, then your B measurement can always be 0, and the math just got easier.

-Mike

Just a quick update on this.... I tried this technique after installing my new FCM bumpstops and dust boots. It worked rather well. Having a ruler that measures in 1/64" was nice, but not really necessary. On a 16" rim-to-rim wheel (my 15" heliums are 16" between lips where I measure), 1mm is 0.14 degrees. 1/64" is 0.06 degrees.

Here's the overall workflow I did:
0) Fire up excel to figure out what the delta between T and B needs to be for your desired camber. I was shooting for about -1.3, or 24/64".
1) get the car on the ground and settled.
2) Position the square so that B is either 1" or 2". With 0 camber, the square would hit the fender at B = 1"
3) Measure T, and subtract B from it.
4) Now figure how how much you need to change T in order to get your desired camber. In my case, B was 2" and T was 2-2/64", so T-B was 2/64. I needed to move it by about 22/64"
5) raise up the corner of the car, so that the top of the rim is up at the top of the square, and you can get at the camber adjustment bolt
6) re-measure with B at 1" or 2", and figure out T. Take the delta you need from step 4, and figure out what your target T is with the car up in the air. As it happened, with the car in the air and B at 1", T was at 1-50c/64. Since I needed to move 22/64", that meant my target T was 2-8/64".
7) Adjust camber and re-measure with the car in the air until you hit your target T.
8) Put the car back down, re-settle it, and double check. Should be within 1/64" or 2.

I think doing the rear would be a bitch, though, because you'd have to adjust both bolts equally. In the front, camber doesn't change too much with caster.

I also stringed up the car and discovered that I'm pretty good at eyeballing front toe.

I also found that the overall front and rear toe is close enough to get me to the alignment shop.

-Mike