Air suspension and front end alignment

[python357]

I tried to do a search on this and coulden't find anything so I figured I'd ask. I noticed that the alignment on the car changed as the air bags inflated while it was on the rack. Questioned the tech on it and he thought the air shocks were bad and I said it was normal. I had brought this up with the tech to see if he would align the front end with the ignition on to keep the shocks inflated he didn't.
So I guess my question is: Does the alignment procedure require full air shocks?
Just something to think about.:lol:

[Rider90]

We don't have front air shocks, just rear air bags...I'd find a different "Tech" next time :baaa:

[dlginnc]

Is ride height an important parameter in the pre-alignment checklist?

[mcb26]

I've wondered that too. Rear ride height does change front end geometry.

[Warpath]

Sorta. The change in rear ride height will primarily affect caster only. Camber and toe are not affected - maybe theoretically. Caster is the angle of the line between the upper and lower ball joints relative to a vertical line (perpendicular to the ground) when viewed from the side of the vehicle. As the rear ride height changes, the frame and suspension pivot about the front tire and move the ball joints fore and aft. Simple trigonometry (sp?) will tell you how much the rear suspension has to move to create a 0.1 deg caster change. The change in frame/body angle when viewed from the side is added or subtracted from caster.

Typical air suspensions will not keep the ride height in the exact same place. There is usually an acceptable range. The air suspension will not react until it is out of that range. Then, it will put it back somewhere in that range. I would expect it to shoot for the middle and the accuracy of the system will determine where it ends up. So, you could get one caster measurement one day and another one a different day since the air suspensions are at different heights. However, Hunter alignment machines calculate caster and don't measure it directly. The problem is that it usually isn't calculated correctly or consistently (within tenth of degrees).