Vehicle "rise" while towing.
Have towed for years with various vehicles. And have always followed the general rule of levelling the tow vehicle front, back to pre-tow hookup. In fact, I just read through most of the Sticky at the...
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I'll add some to what I learned along the way on why "now" the automakers are recommending the front axle of the truck be lighter when using a WD hitch setup.
The NHTSA in the mid 70's hired an engineering firm to study the effects of towing trailers with different sized tow vehicles when towing on the ball behind the vehicle. This was aimed at both cars and trucks of the time as there where many accidents involved while towing a trailer. I printed out that almost 1" thick report back I think around 2005 ish time frame. It was public information you could find on the web, if you knew to look for it.
A point I picked up on in the report, the engineering firm was recommending when using a WD hitch, the front of the tow vehicle should be lighter then when unhitch to help ward off "oversteer" which can lead very quickly to jackknife and loss of control of the vehicle. See here what oversteer is. https://en.wikipedia.org/wiki/Understeer_and_oversteer#
A prime example given was, on dry pavement, the grip of the tires on dry pavement is increased when towing a trailer due to the increased vehicle weight. When heading downhill (trailer inertia is pushing the truck) and the driver makes a quick steering maneuver (for what ever reason) the front tires could bite in so to speak creating an oversteer situation and the tow vehicle can quickly go into an uncontrollably jackknife.
To help ward off, oversteer, the lighter front axle will help slide the truck rather then bite in and go into jack knife.
That was mid 70's recommendations. Then I forget exactly when, the SAE maybe 2010 to ~ 2012 ish, started talking about Front Axle Load Restoration (FALR) and they recommended the front axle of the truck be lighter then unhitched when using a WD hitch. But they never stated why, I connected the dots that it may be due the oversteer concern.
Soon after the SAE came out with their recommendation, after a while GM was first, then Ford, then Dodge started to put in their manuals to have the front axle lighter when using a WD hitch. I have not found there is total agreement on how light, light is supposed to be.
This change in thinking also went into the WD hitch manufactures and it took them a long time to change their older ways of level truck or equal squat on all 4 wheels was the right way to set WD on a tow vehicle. I'm sure there are still some WD makers that have not changed their instructions.
Hope this helps,
John
The NHTSA in the mid 70's hired an engineering firm to study the effects of towing trailers with different sized tow vehicles when towing on the ball behind the vehicle. This was aimed at both cars and trucks of the time as there where many accidents involved while towing a trailer. I printed out that almost 1" thick report back I think around 2005 ish time frame. It was public information you could find on the web, if you knew to look for it.
A point I picked up on in the report, the engineering firm was recommending when using a WD hitch, the front of the tow vehicle should be lighter then when unhitch to help ward off "oversteer" which can lead very quickly to jackknife and loss of control of the vehicle. See here what oversteer is. https://en.wikipedia.org/wiki/Understeer_and_oversteer#
A prime example given was, on dry pavement, the grip of the tires on dry pavement is increased when towing a trailer due to the increased vehicle weight. When heading downhill (trailer inertia is pushing the truck) and the driver makes a quick steering maneuver (for what ever reason) the front tires could bite in so to speak creating an oversteer situation and the tow vehicle can quickly go into an uncontrollably jackknife.
To help ward off, oversteer, the lighter front axle will help slide the truck rather then bite in and go into jack knife.
That was mid 70's recommendations. Then I forget exactly when, the SAE maybe 2010 to ~ 2012 ish, started talking about Front Axle Load Restoration (FALR) and they recommended the front axle of the truck be lighter then unhitched when using a WD hitch. But they never stated why, I connected the dots that it may be due the oversteer concern.
Soon after the SAE came out with their recommendation, after a while GM was first, then Ford, then Dodge started to put in their manuals to have the front axle lighter when using a WD hitch. I have not found there is total agreement on how light, light is supposed to be.
This change in thinking also went into the WD hitch manufactures and it took them a long time to change their older ways of level truck or equal squat on all 4 wheels was the right way to set WD on a tow vehicle. I'm sure there are still some WD makers that have not changed their instructions.
Hope this helps,
John
