4aSong wrote:
From all the readings on weight distribution hitch setup my understanding is that the tow vehicles front axle should measure the same as or less than the unloaded (dry) height of the tow vehicle. My understanding is that it is better to be a little heavy (1/4" drop) on the front to eliminate the "float" or light steering of the front end.
Mike, my usual response to the question of restoring load to the front axle is:
Using a WDH to transfer too much load to the front axle can lead to undesirable TV oversteer. Some TV and WDH manufacturers, in the past few years, have changed their WDH adjustment recommendations.
I think the reason Ford, Chevrolet, Toyota, Equal-i-zer, and others have changed their weight distribution specifications is pretty well summed up in this
Letter to Editor by Richard H Klein, P E printed in TRAILER BODY BUILDERS Magazine. The comment which specifically addresses front axle load is:
QUOTE
2. The statement โtoo much tongue weight can force the truck down in the back, causing the front wheels to lift to the point where steering response and braking can be severely decreasedโ is not the real issue with heavy tongue weights. The real problem is that the tow vehicle's yaw stability, as measured by โundersteer gradientโ, is severely decreased. This increases the propensity of the tow vehicle to jackknife in turning maneuvers. Specifically, recent full scale testing conducted by the SAE Tow Vehicle Trailer Rating Committee (and now published in SAE J2807), determined that the use of weight distributing hitch torque should be minimized. In fact they recommend that the Front Axle Load Restoration (FALR) not exceed 100% (100% means that the front axle weight is brought back, via weight distribution, to a weight equal to its โno trailerโ condition).
UNQUOTE
A related explanation from a representative of the company which manufactures the Equal-i-zer hitch was first posted
here. It says:
QUOTE
In the past we had suggested that you should see a small drop on the front suspension. We are always trying to improve things here at Progress โ our motto is โSafe and Happy Customers,โ and so we are always reviewing our instructions and installation process. Recently, as part of this constant effort our engineers looked more deeply into this aspect of installation. We had always felt that a small drop was a sign that the trailerโs weight was being transferred to the front axle, and that this was essentially a good thing.
As our engineers reviewed the instructions for the last round of renewal of our instructions, the found research results that contradicted our prior thinking. There has been a substantial amount of testing conducted by experts from SAE and the RV Industry Association to find out what will produce the best stability when towing. This towing suggests that you want your front axleโs compression to be close to, but not lower than your free-standing height.
(Underline added for emphasis.)
UNQUOTE
Ford says the Front Axle Load Restoration should be approximately 50%.
Chevrolet/GMC says the FALR should be 100%, 50% or 0% depending on TV model and TT weight.
Equal-i-zer says the Front Axle Load Restoration should be between 50% and 100%.
Equal-i-zer's revised instructions specifically state:
Good adjustment:
You have most likely achieved good weight distribution adjustment if your measurements show the following with the trailer coupled and the weight distribution engaged:
1. From the coupled without weight distribution measurement, the front wheel well measurement is at least halfway back to the original uncoupled measurement. See line C on Front Wheel Well Measure Chart.
2. The rear wheel well measurement is somewhere between the uncoupled height, and the coupled with no weight distribution height. It should NEVER be higher than the uncoupled height. See line C on Rear Wheel Well Measure Chart. See Figure 19.
Ron
