Vehicle "rise" while towing.

[marpel]

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 top of this sub-forum, where it states "GMC specifies that 100% of the rise should be eliminated". Keep in mind that this sticky is quite old (although some new to towing may still refer to it).

Have been reading through the manual for a new Sierra 2500/3500, and in the towing section it describes measuring the pre hookup front height (H1), then the post hookup height (H2). Then set the WDH so the new height is 1/4 of the difference between H1 and H2, below H2. So if H1 is 30 and H2 is 32, then 32-30 =2 and 1/4 of 2 is .5, which is subtracted from H2, so front height while towing and with WDH would be 31.5.

I have never owned a 2500, so wonder if this is HD specific or if this is now the recommended method for towing with all GMC trucks (don't know about the other makes)?

Marv

[Grit_dog]

^How do u “put” your weight to 50/50 or 48/52 or whatever?
Of course you can adjust the weight bias a bit with a wdh IF you use one, or IF you are towing a trailer that is even possible to use one on.
But it’s only by coincidence or maybe very careful planning and a specific trailer tongue weight and the placement or removal of additional weight on the truck (or trailer I suppose) that you could even get to your ideal 50/50 bias.
I agree with you on the weight bias concept, if your post is 1000% mis leading to anyone who would actually find this discussion beneficial, because you can’t just “do” what you’re saying without everything I said above magically falling in place or some ridiculous gyrations with adding or subtracting dead load somewhere.

[Turtle_n_Peeps]

Towing; as with most things in life are a compromise. The manufactures are also saddled compromises.

Some say to bring the front end height 100% back to non towing status. Some say 50%. Some say even less.

I say those numbers are useless....or next to useless and here is why.

Essentially, you want all four tires to have the same weight on them whether towing or not. When all four tires have the same weight on them handling and braking is optimized. Ever wonder why trucks now days have the engine jammed up under the dash? Some mechanics think its to make them mad but the real reason is to get the weight bias as close to 50/50 as possible. Now you know.

That being said the proper way to do a towing setup is to weigh the vehicle and try to make all 4 tires the same weight on your tow rig with your trailer attached.

One could have two trucks with drastically different weight biases. Case in point is a 2500 Ram with a Cummins in it. The Cummins engine is very heavy and the Hemi is light. That being so, I would put more weight on the rear of the Cummins truck and less on the Hemi truck to make all four tires do the same work even though both are 2500 series truck.

Now, if you set up your truck while towing with a 50/50 weight bias you will have optimized handling but braking won't be optimized. (there is that compromise again) Under panic braking with a 50/50 weight bias vehicle a lot of weight goes to the front of the vehicle and the rear tires do very little.

For "me" I put somewhere around 48/52 front to rear weight bias in my truck/trailer towing combo. This seems to make the best "compromise" for "me" for handling and panic braking.

[Boomerweps]

I want to thank those who discussed the oversteer/understeer aspects.
It now makes more sense to me that the F150s with tow packages come with a heavier, solid front anti-roll bar vice the standard same diameter hollow bar and the effects that has. And that there is no factory rear bar.
It has also helped me make up my mind on NOT getting the Hellwig rear bar. While that would improve daily empty driving, I now think that it would not help towing at best and possibly be an actual oversteer concern while towing. Throw in the recent increased cost of the bar & its now a no go for me.

[ktmrfs]

yup, hit the nail on the head. I think few sales guys understand WD hitches and the installers if the do aren't the ones that interface with the customer unfortunetly.

John all the folks I helped had very little knowledge of how a WD system works and the dealer did a WD setup with an empty trailer. Unlike them, I had some knowledge of WD setup and redid mine once I loaded up. And I happened to hit this forum with info from you and others on setting up WD properly.

And like you mention GM front bump stops only have 1/2" of clearance or less, so don't try to drop below unloaded height.

And for hookup I've had a few people who tried to hook up with the TV trailer combo in a "V", when in a sloped driveway to the street and they don't realize that the "V" adds a great deal of load to those bars, can be dangerous unhooking if not careful or very hard to hook up even by using the jack to lift the tongue. Once I gave them a physics lesson they had an "ah ha" moment and they realized they just need to pull the trailer out of the driveway and get flat in the street then hook up the bars.

[JBarca]

ktmrfs wrote:
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.

Hi ktmrsf,

By chance were your friends who you helped, first time TT owners, or their first time using or adjusting a WD hitch?

Yes, I agree, many first time TT owners, never had some one explain to them or did they understand what a WD hitch is supposed to do. The dealer setup the tow rig with an empty trailer, and many times, an empty truck and down the road the new owner goes.

Then the new TT owner, loads the camper and the truck. The TT tongue weight changes, the truck suspension changes, yet the WD settings are left from an empty camper.

Then there is the misunderstanding on how to hitch up when using a WD hitch and how to use the trailer tongue jack to lift the camper way up, then snap up the WD bars.

This adds up to, the new owner thinking, wow these WD bars are really tight, they for sure do not need any more adjustment. And they end up with the front end of the truck being very light and the rear axle, very heavy. The truck handling is bad, and having a lighter truck can make it all that much worse as the the lighter truck really needs the benefit of a WD hitch adjusted correctly.

Close to the same thing above happened to me on my first TT. While I had towed many trailers, open deck, sail boat, enclosed cargo trailers, I never towed a TT needing a WD hitch. So I asked the shop PDI person, what do I need to understand or do to adjust this WD hitch? He stated, just take up a link if you want to move more weight. They wanted to explain more on how to work the appliances inside the camper then a WD hitch or trailer running gear. I was green enough then to not ask further when, why and how do you know what to adjust on a WD hitch? Then the learning started. My one year old 2002 1/2 ton Tahoe was out of cargo capacity the day I filled the camper with cargo. And the 800# WD bars the dealer gave me on an 800# dry tongue weight camper were also, very wrong even after I stated, are you sure I do not need the 1,200# bars? He said no, I would not send you down the road with a miss matched setup.

When I got home and started loading the camper, I realized my mistake as tow ratings are very misunderstood if the truck can't handle the loaded tongue weight of a TT. Before I got myself into an bad situation, I fixed the weight issue changing the truck to a 2003 K2500 Suburban and then even more learning started.. GM torsion bar front ends will not drop once the yellow jounce bumpers hit. I have always said, you learn a lot more when things go wrong...

It too have since helped many, many fellow camping friends understand the same error of my ways and adjusted them back into a very stable towing setup. Some though had to change the truck too.

Point: It is common to have handling issues from the WD hitch being very out of adjustment. And the WD hitch is only one of many factors in a stable towing rig. But it starts with proper TW on the camper, then proper WD adjustment, then comes all the other factors, tire pressures, trailer towing stance, is the truck overloaded and the list goes on.

Experience is something that is learned, over time, you are not born with it. 🙂

[ktmrfs]

BenK wrote:
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.

at least as late as 2016 GM had a rubber bump stop on the front axle that is about 1/2" below the unloaded front end position. It's been easy for me to get the front back to unloaded height, but if you overdo and hit the bump stop or attempt to do the old " get the front and rear to drop the same amount", yes, almost no amount of spring bar will drop the front below unloaded.

[BenK]

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.

[Grit_dog]

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.

[ktmrfs]

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.

[JBarca]

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

[BenK]

What Marty said...

[ktmrfs]

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.

[blt2ski]

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

[Campfire_Time]

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.

[Boomerweps]

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?