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

[BenK]

Lamborghini started out in the tractor business, before exotics & super cars

Story is similar to the current "Ford vs Ferrari" movie...Ferrari told him to go back to building tractors after he made an offer...

Even drop...goes to the fact that front vs rear suspension spring rates are different

So even drop gets the TV back to factory suspension bias

But, with the OEMs now all over the place in regards to how they design & setup TV suspensions...follow their manual recommendations

[valhalla360]

Wade44 wrote:

Turtle n Peeps wrote:

Hence the reason they plow like a John Deere in the back 40 field.

My JD's handle like a Lamborghini out on the back 400.

Warning: Thread drift.

Considering Lamborghini started as a tractor company is that surprising?

Historically, they were never known for great ride or handling. They were weird and wild over the top noise makers...is that what you are implying your JD is?

[Grit_dog]

^Thats because I have no idea what the recommendation is! Never used a wdh yet for any trailer behind any truck I’ve been behind the wheel of. (To be fair I did try to hook my toyhauler to my 1500 Chevy with the previous owners wdh he gave me with the trailer. It didn’t help that poor little truck much…)
As far as my opinion on it goes. “IF” I needed one to help out my suspension, I would likely just go by how it felt, driving, with respect to understeer and what it took to get the back of the truck up to an acceptable level of sag.

[mkirsch]

marpel wrote:
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

Funny nobody, not even Grit Dog, answered your question about GMC trucks.

In fact the first response referred to an F150.

The answer is "Yes, most likely, but you should refer to the owner's manual for each truck to verify, as recommendations could have changed further."

The recommendation has gone from "even squat front and rear" to "100% of unloaded height" to "50% of unloaded height" and apparently now in some cases to "75% of unloaded height."

Scientifically, returning the front end to unloaded height means the same amount of weight is on the front tires after hitching as there was before hitching. This ensures your front end steering and braking is as effective loaded as it was unloaded.

[Grit_dog]

LOVE BotP posts!!

[BackOfThePack]

Boomerweps wrote:
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.

Load the pickup 50/50
Hitch, and set the WDH correctly using CAT

Test with & without rear bar.
There’s no comparison

Loss of rear traction greater WITH rear bar if truck not loaded.
They’re assuming you’re a softball daddy runs around empty.

.

[BackOfThePack]

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.

It’s my impression that all pickups today have FF/RR anti-roll bars. On a leaf-spring pickup without a rear bar, yeah, install smallest rear and upsize front a minor amount (must be larger than rear by a %). LITTLE otherwise has such a beneficial effect. Trailer CANNOT exert anywhere near the force of moving the pickup bed against a pair of bushings as truck can now counter it.

KONI or Bilstein shock absorbers. MICHELIN or Bridgestone tires on stock rims with tread & rim width match. SECURE everything in the bed.

— Hensley hitch (or improved patent Pro Pride) eliminates most of the problems. Advantage of 5’er type hitch, but better than those as NO SWAY possible (after best scaled set-up).

.

[BackOfThePack]

Wade44 wrote:

marpel wrote:


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

Having towed just about everything imaginable from trailers full of hay, to livestock, to you name it my entire life on the farm, with everything from 3/4 ton Fords and GM's to F450's, and at weights which were totally overloaded in a lot of cases, I find it hard to believe you're going to be able to measure any front end rise on a HD truck when loaded down towing conventionally or otherwise.

Cat Scale.

And trailers without the side-sail area of a TT aren’t a comparison which matters. Not
a weight question. It’s a STEERING question.

The majority of loss-of-control accidents are wind-induced. TT gets airborne (keel over)
and it’s down to steering degree & duration. “Feel”.

Sudden crosswind is enough. Man-made or naturally occurring.

Plenty of Utube vids of tractor trailers getting lifted from rear before going over.

TT needs to be dead-level after WDH applied. (Carpenters level across doorway). Need all the side-sway resistance four tires can bring to bear (as the two on the TV can’t do it alone), and to MAXIMIZE braking of both vehicles. Countering nose down tendency. (4-axle braking over 2-axle rig total).

TEST.

[BackOfThePack]

Equal Squat to rough-in at home.

The ancient formula is 1/3-1/3-1/3 distribution.

CAT Scale to confirm Steer Axle same Solo or Towing.

(Scale numbers are placeholders).

The percentages matter, not what you “think” is okay (hundreds of pounds removed),
since road-going dynamics can create gigantic shifts in force.

That long lever from TT axles to ball (and next from ball to Drive) need all
the help they can get to reduce force applied at ONE point.

SAE is captive engineering. Reflects what $$$ wants.
J2807 isn’t a standard as one can drive a pickup thru it.

NO ONES BEEN ABLE TO REPLICATE the so-called “understeer”.

How do 5’ers/GN load the Steer Axle? 100%


If the TV is a pickup and isn’t at around 50/50 BEFORE HITCHING,
you bought the wrong tow vehicle. (Too much
unused rear spring capacity on a pickup
is part of what makes them lousy tow vehicles).

Mines near GVWR before I hitch. Its 1,100-TW is what cars,
minivans and SUVs do fine with. 425-450/lbs per TV axle
isn’t a burden. Load vehicle type accordingly.

Let go of wheel at 55. Stays on rails for a long three count?
Stops faster from 30-mph hitched than TV solo?

PRESERVATION of Solo steering “action” matters. Degree &
Duration of steering input in emergency is where it goes hinky

TV tires to scaled axle load. Get AT ALL very much above that
to get back that feel is how the 90% finish WDH rigging failure.

Get out and test it. (TT tires to sidewall max).

.

[BenK]

There is lot more than what is currently discussed for both empty grocery getter mode and as a TV

ALL of the components, sub systems and systems matter and play together

Just take tires, wheels and suspension

Ultra low profile (aspect ratio) to traditional 85 aspect ratio matters and plays with...

PSI you have in them and plays with...

Wheel rim width vs the OEM's recommended rim width vs what you did to re-engineer and plays with...

The wheel offset vs OEM offset and plays with...

The OEM shocks to the aftermarket shocks you put on and plays with...

The suspension layout. Such as Live axle, IDR/IDF, Swing arms, leaf/coil, etc, etc and plays with...

The OEM anti-sway (lean) bars or none to the aftermarket you put on front and no rear, to the rear you put on & didn't increase the front bar's rating, to the other suspension modifications you have made and plays with...

The steering system and the ratio & linear or variable rate & how tight it is and plays with...

The OEM bushings and the aftermarket bushing you installed or not with the aftermarket anti-sway bar(s) and plays with...

Whether empty grocery getter mode to TV to performance level driving and plays with...

The ABS system & braking coefficient of materials (mud hen OEM to track level) you have chosen to install and plays with...

The level of OEM thermal rejection management and the aftermarket stuff you have added or modified yourself and plays with...

The rest of the whole vehicle system, which would be the computer management systems and subsystems that came with your vehicle to the aftermarket stuff you have installed...

It is not as simple as most think and the reason OEMs dial in under-steer for the masses who have no clue, nor care in most cases...but this is a very narrow slice of the masses, so assume knows more...but the comments says closer to the masses...


Edit...should have added the aftermarket OEM/model/etc of those components also matters and plays with...

[Wade44]

Turtle n Peeps wrote:

Hence the reason they plow like a John Deere in the back 40 field.

My JD's handle like a Lamborghini out on the back 400. Have you ever plowed a field?

[Wade44]

marpel wrote:


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

Having towed just about everything imaginable from trailers full of hay, to livestock, to you name it my entire life on the farm, with everything from 3/4 ton Fords and GM's to F450's, and at weights which were totally overloaded in a lot of cases, I find it hard to believe you're going to be able to measure any front end rise on a HD truck when loaded down towing conventionally or otherwise.

[Turtle_n_Peeps]

ktmrfs wrote:
Goal from manufacturer for almost all vehicles today is for the vehicle to understeer under most conditions.

Hence the reason they plow like a John Deere in the back 40 field.

There is a reason trucks handle bad from the factory and you hit on the reason. They tried to mitigate the problem by jamming the engine up under the dash but as you said, they still can't get 50/50. (nor do they want too) In the old days people used to put a steel plate in the back of their truck. Or bags of sand. The reasons were the same.....to get the truck to handle better in all conditions.

Like I said above, the goal of a well handling road vehicle is to get all 4 tires working the same. I set my towing truck up where the weight bias is around 52/48 when the trailer is connected. Like I said above, this is a compromise, but a compromise that works well.

If you like your truck to plow like a pig in a turn so be it, but I want a well handling truck when I tow.

[ktmrfs]

Turtle n Peeps wrote:
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.

equal weight NO NO NO, optimum weight is to stay near the factory weight distribution % front to rear. for many vehicles today trucks and cars, that's in the 55/45 to 60/40, range there are only a few vehicles anywhere near 50/50 distribution And few if any trucks.

Goal from manufacturer for almost all vehicles today is for the vehicle to understeer under most conditions.