Vehicle "rise" while towing.

Generally, OEM's setup our pickups and SUVs with understeer with only a front anti-sway bar (anti-lean bar) and NO rear anti-sway bar

Exception are 'performance' (boy racer with lots of GO) where they might have a rear anti-sway bar, but most don't know is that the OEM also increases the front anti-sway bars diameter (higher torsional rigidity)

Why IMO...do not recommend installing a rear anti-sway bar and if insist, then to make sure to also change the OEM front anti-sway bar to a larger dia from the SAME after market suppler of the rear bar being installed

With that in mind, the old 'even drop' kept the above handling characteristics, but with the newer suspensions & the new 'drop' or 'return the front axle' recommendations...that 'even drop' has been put aside

I still adhere to 'even drop' for my setups. Maybe not if I ever get another +8K GVWR TV and know that GM's newer 4x4's has a secondary front axle spring in constant contact with the lower A-Arm and can NOT bring the front back to OEM height easily. Else there would be too much WD'ing weight off of the TV's rear axle

Glad to read John mentioning that 'push' trailers impart onto the TV's rear end. And during a freeway speed curve while braking, the trailer will both nose dive during braking to add weight to the TV's read end and 'push' it trying to go 'straight'.

That is where manhandling the setup comes into play.

Honest question. Do y’all think there’s any material differences in the vehicles reccomending different levels of “rise?”

Answer, no there’s not. It’s simply how much weight transfer is needed or desired based on about every factor except being specific to a specific vehicle.

JBarca:

good info that seems to shed light on the changing recomendations.

I'll also add my experience related to 4 people I've helped set up a WD hitch. This was after they complained to me that they felt the trailer was giving them sway and didn't feel comfortable with the way the combo handled.

In each case looking at front "rise" measurements and rear "Sag" measurments I found that the front was always high compared to unloaded and not bringing the front back to even 1/2 the difference. Once I adjusted the setup to bring the front back to at least half or more of the distance (I was shooting for close to unloaded) the problems went away and they were amazed at the difference in handling.

At the time my thought was that with the front end rising they were getting more camber on the front axle which coupled with a lighter front end, heavy back end was letting the front end be to sensitive to steering correction.

Yes, in the extreme it would probably oversteer rather then understeer.

My conclusion after helping all the folks I did adjustment for was to keep increasing front load (dropping the front) till the wander problem disapeared. it seem to take bringing it back to at least 1/2 the difference to be effective.

Now all this was done on smaller lighter vehicles, <1/2 ton trucks, Suburbans etc.

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

What Marty said...

on our 2500 GMC (2004 and then 2015) I adjusted to bring the front down to slightly above unloaded. CAUTION. DO NOT drop it below unloaded on GM, you'll hit the rubber bump stops quickly and really make the ride rough.
the manual on both the 2500's said to drop it 1/2 way between loaded and unloaded.
My suggestion is to try what they recomend, then drop it to 1/2 and compare and then drop it back close to empty and see which handles best.

One issue is that on most trucks as the front rises camber changes noticeably and camber can affect how the truck handles and end up with front end "wander" that seems like trailer sway.

I've always figured, if both truck and trailer are level, it's setup correctly.
If the TV is rear low, needs fixing by a WD, beefier and/or springs so the rear does not sag as much.
Also, if I can't tow the trailer at 60mph without sway, then I need to figure out the cause of the sway before adding the Peterbilt bandaid in my book to stop sway.
I could go on about more things too.
I've only used a WD on my RV trailer. The other half dozen trailers I've owned, or add a few dozen more rented, have all been dead wieght towed

Marty

It specific to the truck. My old '08 Sierra 1500 said back to stock height. My current 2016 Silverado 1500 says half way between the 2 measurements. I was skeptical but it towed effortlessly and very stable.

Just try it and drive it. If it doesn't feel right you may need to take it to a CAT scale.

1/4 of height difference returned to the front? Man, I thought the 1/2 returned recommended by Ford wasn’t enough.
I, too, shoot for TV returned to close to level. In part, because that front only measurement discounts any rear drop. To me, it’s just not logical. Even fully returning the front to the unloaded value, the rear may sag. It appears the vehicle makers are just worrying about loss of front wheel traction for steering and the partial returned value is adaquate.
So I shouldn’t get mad at people towing with GMs at night blinding me cause they were just following orders?

My Ford F-150 manual says to return half of the rise. I think the main thing is to replace SOME of the rise to ensure you have sufficient front tire grip on the road, without overloading the front axle. The precise details probably don't matter a whole lot.