Ford - Unhitched vs Hitched Fender Height

Bob Landry wrote:
Just got a new F250, so I have to redo my WD. I'm going to split the difference between the two heights because that's what Ford says to do, but I'm a little curious why you would not want to return the same amount of weight to the front axle.

From my research on this, part of the thought process has to deal with oversteer when towing.

http://en.wikipedia.org/wiki/Understeer

The concern is that with the mass of a trailer pushing the truck, if the front is heavy or extra heavy from more than unloaded weight, that the front wheels can bite in so to speak in a turn from a firm grip to the pavement and send the rig into jack knife from oversteer. This is a very negative thing.

SAE (Society of Automotive Engineers) have done tests on this in the last few years and are now recommending that when towing to try and avoid this oversteer condition. Equal-I-zer by Progress Mfg even changed their tune too. They use to recommend driving the front end down below unhitched. Now they too have changed theIr ways in light of the SAE findings.

This is not really a new thing, it was know long ago, just it is now coming to the forefront as a better method when towing. Back in the late 60's/early 70's an engineering firm was hired by the NHTSA to study the effect of towing trailers with certain vehicles. In this study this effect came up along with a lot of other things. If your really into this and want to read it, let me know I'll hunt it up. I have it printed out, about 1" thick and lots of detail. It is public information. Ron Gratz pointed me to this a long time ago.

On my 2005 F350 Ford or other SD's of the time, they allowed +/- 1/2" from unhitched height on the Front. In my case I found running the front about 75 to 100# lighter on the front created a more stable tow. This was not from the oversteer concern, but do to the F350 rear suspension. When I returned the front to unhitched height, the heavy TW camper rocked the back of the truck to a noticeable point.

When I backed off a little WD, the 1 ton helper springs (overloads) just kissed the frame brackets and created a global shift in left to right stability.

The F350 way up high in it's suspension when the truck is empty is fairly soft, when you load it, it then becomes more stiff.

The are objectives to meet when setting up WD, however there are also vehicle characteristics that one size fits all is not an absolute. My 2003 K2500 Suburban towed very well when just above front end unhitched.

Point in this, 1/2 ton, 3/4 ton and 1 ton PU suspensions are different. What you can do with a 3/4 or 1 ton is different than a 1/2 ton. Running the front end of a 1/2 ton real light and the rear close to max axle capacity is not good either. While oversteer will not be a concern, the trailer mass pushing the truck can affect front end steering. Not enough weight and you get understeer.

Good luck with your new truck.

Hope this helps

John