An Alignment Question

[Bob In Ct]

Because most snakes have a wider track in the back than the front I have wondered how the new alignment machines deal with this lack of "square".

Although I understand castor, camber and toe-in, I have trouble understanding how the modern alignment machines measure it. When the tech is hanging the whatevers on my wheels how do the gismos know that the track in the rear is greater than the track in the front? If the machine assumes the wheel base is square will I end up with a bad alignment?

Any ideas out there?

Bob

[speed220mph]

Bob,
See photo of a car you should be familiar with ERA 2002. The tech is setting up heads on each wheel . . . turn plates are under each wheel for four-wheel alignment.

The alignment machine shown is an older system using cables to each head that projects a light beam from the heads to a receiver. Newer machines such as those from Hunter use "targets" that reflect light projected from laser beams onto the targets and bounced back from each wheel to a receiver. Once "compensated" by rotating the wheels, lowering the vehicle, then rolling it out, each wheel is read individually for camber and toe. Steering is turned right and left, then centered to get a caster readings. Sure beats the old caster gauge, strings, level and chalk marks on the floor.

[Bob In Ct]

But how does the machine know that the back wheels are farther apart the the fronts? You can tell the machine that you have a 92 Mustang or 89 Vette, but how do you tell it that it's a 2000 SPF? Why wouldn't the head in the back think it's right behind the one in the front?

Bob

[speed220mph]

For the cable type, all you have to do is connect the cable to the specified corner. As for targets, the computer knows which corner you're working with when doing the compensation. As for front vs. rear tread, the computer either knows the car when you specify it, which has the stored data for that car or you just do a swag. Caster, camber and toe at either ends aren't affected by front vs. rear tread differences. Dog tracking is shown, though.