Which static alignment specs are directly adjustable on a stock 2wd 3rd-gen 4runner?

[foo]

SAI is the same measured points as Caster, only the angle is viewed from the front of the vehicle, as opposed to the left or right. This page has a good basic view.

Wheel Alignment Explained

I thank you for that wonderful hint that the SAI is just a different plane with the same endpoints as caster, where those two diagrams show that once you mentioned what I am to look for.

Your hint helps me base my thinking on a few concrete points of knowledge to reference.

If you hadn't mentioned that they're just two sides of the same cube (so to speak), I wouldn't have known what to look for.

It seems this suspension stuff takes about a score of little things that you have to take on faith, and when you add up those little things, they equal the big picture.

So please bear with me as I will be slow to uptake the equations because I can't take any equation on faith until I at least understand where they came from (it's a flaw of mine that I have to work on).

 

[foo]

Caster = (CamberA - CamberB)/(2*sin(A))

Where (CamberA - CamberB) is the algebraic difference of the two measured camber angles. E.g., if CamberA=+1.5 and CamberB=-1, (CamberA-CamberB)=(1.5-(-1))=2.5

I love that you posted this final (simplified, practical) equation as I can easily plug in the measured camber at 20 degrees inboard and outboard to derive caster.

I'm slow though - as I have to see that equation elsewhere to trust it and, when I look elsewhere (such as the Hunter explanation), I see different simplifications. I'm sure they're the same in the end - so I am just trying to make the Hunter equations match with yours above.

I'm not successful yet in deriving your equation above from the Hunter equations - but I'm working on it so please be patient with me as I'm slow on the uptake side because I take nothing on pure faith (unless there is no other option).

The Hunter equation (see below) that I *start* with is the following:
Caster = (180/pi)(CamberMeasuredInboard - CamberMeasuredOutboard)/(DegreesTurnedOutboard - DegreesTurnedInboard)

All I'm trying to do right now is get from that equation, to yours.

 

[RonJR]

The Hunter equation is another simplification, in that it drops the sin function in favor of the assumption that, for small angles, the sin (or tangent) of an angle is very nearly equal to the angle itself in radians.This works well for angles under 15 degrees (where the error is about 1.1%), but as the angle increases the error increases as well (~2% at 20 deg, 4.5% at 30 degrees, etc.) My equation does not make this simplification in the denominator, since the steering angles can be fairly large (20 deg or so)

However, I do make that simplification in the numerator, because the measured camber angles are indeed very small (<5 deg), so the error there is <.15%).

That gives you the final equation I posted,
Caster = (CamberA - CamberB)/(2*sin(A)), which is essentially the simplified Hunter equation but slightly more accurate.

 

[foo]

I do make that simplification in the numerator, because the measured camber angles are indeed very small (<5 deg), so the error there is <.15%).

That gives you the final equation I posted,

Thank you for explaining the simplifications of the Hunter equation and yours, where, I must admit, I wasn't able to figure it out on my own - so I very much appreciate that you did that for us.

The great news then, is twofold, in that measuring camber gets us caster, and plugging in the measured camber into either equation can be used to check the results, where they should agree within some reasonable amount.

1. Caster = (CamberA - CamberB)/(2*sin(A)), which is essentially the simplified Hunter equation but slightly more accurate.
2. Caster = (180/pi)(CamberDegreesMeasuredInboard - CamberDegreesMeasuredOutboard)/(WheelDegreesTurnedOutboard - WheelDegreesTurnedInboard) which is the Hunter equation which is best for steering toe angles less than 15 degrees