alignment math, all you numbers guys check my math!! Options

[jaybird840]

OK,

I'm working on a home alignment on my teener, and am trying to calculate my camber adjustments. I can't use the bird board measurements because I'm running 18" wheels. So, in order to get an adjustment measurement, I calculated the circumference of my wheels--outer lip to outer lip (this is where I take my measurements). C=diameter x pi--right? So if my wheels measure 19.5", then the circumference = 19.5 x 3.14159 which gives a circumference of 61.26". If you divide the circumference by 360, then 1 degree = .17". In order to run 30" of negative camber, I divide by three again to give me .05" or 1.43mm. Now, in order to achieve that number, I must multipy by two to get the actual measurement from the bottom of the rim to the top of the rim, right? Long story short, my measurement needs to be 2.86 (call it 3mm) greater at the top of the rim than the bottom of the rim, right? I'm a cop, not a math genius, so you engineers feel free to chime in.... thanks tons!!!!!

While on the subject of alignments.... What should the toe in measurements be in degrees? Am I right that a 32nd on 15's is different than a 32nd on 18's?

--jaybird

[byndbad914]

how funny... I just put 3deg neg camber and 1/8" toe in the rear yesterday with a laser pointer and a tape measure/simple angle finder. It works just as well as any camber gauge I have ever used frankly and cost me less than $20 IIRC. Key is to have a level floor when you do this stuff.

I set the camber to where I want it with the angle finder and a flat sheet of alum across the tire. Then when I want to set the toe, I use a laser. I shoot the plane with the laser and with a tape measure I get the plane parallel to the chassis of the car. Then I simply measure the front and rear of the tire 13" up from the ground to get toe. I set the rear at 1/8" toe-in by setting one tire to 1/16" with the laser, then use toe plates to set the other side cuz it is easier to match them to each other than futz with the laser a second time.

It is important to either go thru all the pain of strings or just use a laser on at least one side (I can have that laser set up in under 15 minutes) to get one side square to the car itself. The other side just needs to be toed relative to the other side.

If you try to set camber with a tape measure against the tire, you need to understand the bottom of the tire bulges out under the weight of the car, so your measurement will be bogus and you will have less camber than you thought because you measured the bottom out further than it really is.