Originally Posted by Mike Magee
I do not believe that adding air to the rear suspension can shift weight to the tow vehicle's front tires
. The same weight is still in the same place on the ball and on the rear suspension; the air merely stiffens that suspension and helps it carry the weight. If weight has been off-loaded from the front axle
via leverage, that weight remains off-loaded even when air is added to the rear shocks.
Whether a WDH is "needed" or not can sometimes be a matter of personal opinion. Some folks are more averse to rear end squat than others! And some vehicles are more susceptible to it than others; for example, when Can-Am RV outfits a Jetta for towing, they always include WD to redistribute some weight to both the front axle
and the trailer axle. One factor is the tow vehicle's rear overhang length; the more of it you have, the more leverage is applied by the trailer and the more weight is shifted off the front axle (in the absence of WD).
Your statement is exactly correct.
This is why the VW Golf is rated better than the Wagen - more overhang!
In Europe many cars are equipped with HID lights
and they are required (as in the US) to have self leveling features, either the suspension or the lights
I chose the air bags to level and get the light
correct AND to keep the suspension alignment correct.
Another benefit of the air bags is the stiffening of the rear springs. This raises the resonant frequency of the back and helps prevent the oscillation inception.
When springs are loaded there is a frequency that the springs resonant, adding weight lowers that frequency. If this coincides with the frequency of the coupling of the trailer / car combination any deviation will tend to increase and not be damped. At this point the dreaded sway starts and increases.
The resonant frequency is increased with the square of the speed and at some point this frequency matches the resonant frequency of the tow vehicle.
The air bags let you selectively increase both the ride height and the resonant frequency of the rear end.
In other words the stiffer the better. (within reason).
The spring rate is measured in inches of deflection per lb of load.
Obviously if the spring has been raised 1 1/2" the rate has been increased. Also the bag adds damping with the friction between the bag and coils