I went to a few alignment shops around here and they all said that they will only do a 4w alignment, vs just TOE. Reason I only care about TOE is cause I need crazy negative camber to fit my wheels and caster is non-applicable on our DC's unless via spherical FLCA bearings or a traction bar. they were willing to set just the front for me why can't they do the same for the rear ? I have BWR adj toe arms and H/R RTAB's...


does the rear toe even matter that much if you have -6-7* of camber ?

 

On a vehicle with 4-wheel independent suspension, the fronts are dependent on the rears.

You do the toe on the rears, establish the thrust angle, then align the fronts according to the thrust angle of the rears.

 

The more camber you have, the more toe matters. Camber is exposing one edge to wear. More camber means the wearing edge is more concentrated. So if toe is the fastest wearing angle, and the camber is exposing a concentrated surface to wear, you see where I'm going.

Idk what the question is though. Set the car on the rack. Align all 4 wheels to whatever specs you want.

Are you under the impression that they only put sensors on 2 wheels to do a 2 wheel alignment? They put sensors on all 4 wheels regardless. That's the only way to do an alignment. For a 2 wheel alignment, they only adjust 2 wheels. They still get measurements from all 4.

If the back doesn't need adjustment or cannot be adjusted, they'll just adjust the front 2 wheels. That's a 2 wheel alignment.

 

And even then, those two front wheels will need to be adjusted relative to the thrust angle created by the rears in order for the vehicle to drive and steer true.

In theory, the thrust angle of a solid (live or dead) rear axle should be aligned dead-on with the centerline of the body of the car, but the alignment tech can't know one way or the other until he checks. Therefore, EVERY alignment is a 4-wheel job, even if only two wheels actually get adjusted.

 

Yes. The most simple way to explain it is that you need 4 points to make a rectangle.

 

ok fair enough we learn alignment next year so like emissions/HVAC I'm clueless.

thanks guys

 

See image below:


BOTH are valid alignment setups.

The diagram on the left shows a car with perfect alignment, where the thrust line (centerline) is perfectly perpendicular to the axle lines, and is also parallel to the car's own body centerline.

The diagram on the right shows a vehicle with a thrust line that is not perpendicular; most cars on the road are this way. (This diagram is heavily exaggerated for illustrative purposes.)

The rear wheels will be toed-in, intersecting at some point. You then bisect the resulting included angle. The bisecting line becomes the thrust line. Then you align the front wheels so they run parallel to the thrust line.

That's the starting point. Then the tech has to use his intuition and "feel" to tweak things until the vehicle drives and steers "properly".