How much of rise on front of truck acceptable when hitched?

https://www.rvlifemag.com/taking-the-mystery-out-of-torsion-bars/

https://www.rvlifemag.com/understanding-ball-mount-angle/

https://www.rvlifemag.com/how-to-set-up-a-weight-distributing-hitch-system/


Bars well-chosen and then set at home, take to a CAT SCALE (phone app available) and get the real numbers. There’s an adjustment range from heavy to light with your combined rig. The scale helps you dial it in today, and to diagnose problems in the future.


Three Pass Scale Method (Ron Gratz, back in 2010)
All passengers aboard every time. Full fresh water & propane. Both vehicles loaded for a camping trip.

1). First weigh with hitch tensioned.

2). Second weigh with bars fully slack

3) Third weigh is TV only.

STEER AXLE in #1 & #3 the same (you’re done).
Make adjustments to get close as can be without going over.

A 5’er/GN loads the Steer Axle the same way: no change.

Handling is different of course. But we want steering & braking to be close to the loaded/solo value.

You think you have it close, then test brake control adjustment. SHOULD STOP FASTER FROM 30MPH WHEN HITCHED.

A). Tire pressure take from #1 (or corrected) as against Load & Pressure Table (but not lower than TV manufacturers range). Too much air is BAD idea, worsens braking & steering.

B). Note FF/RR weight bias of TV in #3. Closest to 50/50 before hitching means better outcome. Too much forward = you bought the wrong TV (high rear spring rate not your friend unless utilized in main).

— A 1,000-lb TW is the province of cars. Pickup not needed. The 1/3-Distribution goal means “maybe” 500-lbs static on ball at rest. 10-15% TW which #2 tells you.

The numbers tossed around are placeholders. Towing involves road-going dynamics where the force on the ball can go sky-high, or go super low. The WDH applies these forces across the entirety of the combination vehicle.

Done right, it tracks on rails. Stay with it until this is the outcome. (Anti-sway is a separate subject, but it’ll still need the above).

Andy & his father codified what the rest of us learned more than fifty years ago. That dealership has set up more than 14,000 tow rigs. He’s a consultant on towing to both Airstream and SAE.

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Grit dog wrote:
First, if you can transfer more weight to the front than it originally had, time to re think your need for a wdh or you’re doing it wrong.

It's certainly possible to put more weight back on the front axle than it originally had. There was a marketing campaign back in the 60-70's where they went silly with the WDH (front wheel drive vehicle). They would then drive it around without the rear tires.

In principal, keeping the front/rear axle weight distribution the same would be ideal but in practice it's rarely practical. Setting a limit recommendation avoids 99% of the times when it could cause problems.

Also, need to differentiate front rise from change in frame angle. When empty, pickups typically sit a bit high in the back, so squatting a bit without taking any weight off the front axle can make it appear the front is lifting if just doing a visual check.

Grit dog wrote:



RVing is not totally unique but it’s sort of unique in that most people consider it a right to go RVing when there are no requirements or training necessary to operate something that would otherwise require training or certification in the commercial world. Thus there is an abnormally large % of consumers who are blissfully ignorant about some or many aspects of operating or controlling a heavy vehicle or combo.
When one observes the relatively large % of people who are challenged by simply operating the smallest of passenger vehicles combined with the fact that all it takes is a credit card, cash or a line of credit to instantly be the operator of a heavy vehicle. And not the typical commercial application where there is a greater chance of skill, training or experience or knowledge being gained or passed down then you get information published like this to help people save themselves from themselves.

Reading this statement by somebody that generally knows what he is talking about should scare rational people.

Three Pass Scale Method (Ron Gratz, back in 2010)
All passengers aboard every time. Full fresh water & propane. Both vehicles loaded for a camping trip.

1). First weigh with hitch tensioned.

2). Second weigh with bars fully slack

3) Third weigh is TV only.

I have never understood what useful information is gained with the second pass. TW, the only number for TW that affects handling is TW when ready to hit the road. Can get that by adding S + D together, subtracting gross from third pass. Know if rear axle is overweight before bars are hooked up? Normal hookup, do you get tongue jack off ground before hooking up bars?

valhalla360 wrote:

Also, need to differentiate front rise from change in frame angle. When empty, pickups typically sit a bit high in the back, so squatting a bit without taking any weight off the front axle can make it appear the front is lifting if just doing a visual check.

Can you explain how the "squat without taking weight off"?
Look at a lever on fulcrum. Add weight to 1 end, weight comes off the other end. The fact the fulcrum moves (rear suspension compression) does not change that.

JRscooby wrote:
Can you explain how the "squat without taking weight off"?
Look at a lever on fulcrum. Add weight to 1 end, weight comes off the other end. The fact the fulcrum moves (rear suspension compression) does not change that.

With simple ball hitch, yes, the frame will act as a simply supported beam and yes, it will take some weight off the front axle if you put any weight on the hitch. Of course, with the really long wheelbase trucks (4 door long bed), it takes negligible weight off the front axle while all the hitch weight, all the in bed cargo weight and any weight off the front axle...goes onto the rear axle. So if you take 150lb off the front axle, you might be adding 1500lb to the rear axle when you are fully loaded. The result is...it will be hard to accurately measure any rise in the front axle while the rear axle is likely doing to drop by at least a couple inches (depends on the truck model...1/2 tons will be more duallys less)

But with a WDH, the trucks frame no longer acts as a simply supported beam, so you can't consider it a simply supported beam.

valhalla360 wrote:

JRscooby wrote:
Can you explain how the "squat without taking weight off"?
Look at a lever on fulcrum. Add weight to 1 end, weight comes off the other end. The fact the fulcrum moves (rear suspension compression) does not change that.

With simple ball hitch, yes, the frame will act as a simply supported beam and yes, it will take some weight off the front axle if you put any weight on the hitch. Of course, with the really long wheelbase trucks (4 door long bed), it takes negligible weight off the front axle while all the hitch weight, all the in bed cargo weight and any weight off the front axle...goes onto the rear axle. So if you take 150lb off the front axle, you might be adding 1500lb to the rear axle when you are fully loaded. The result is...it will be hard to accurately measure any rise in the front axle while the rear axle is likely doing to drop by at least a couple inches (depends on the truck model...1/2 tons will be more duallys less)

But with a WDH, the trucks frame no longer acts as a simply supported beam, so you can't consider it a simply supported beam.

So you agree adding weight anyplace behind rear axle will reduce weight on front axle. And I bet somebody that paid attention in gee, I'ma tree class could tell you how much if given the amount of tongue weight, distance rear axle to ball, and wheelbase. Now like you say, without knowing the front spring rate, and what percentage of the front axle weight is moved no way to predict how much the bumper will lift. But the fact the rear suspension compresses does not change the amount of weight transferred.
As a pro, I never had much to do with WDH. But just another lever. Fulcrum is the ball. Force applied to trailer end, the load is what is trying to counteract movement the weight on rear axle causes in frame.

See this thread - at least the first post by my friend Ron Gratz (may he rest in peace).
Barney

I still don't understand the need to weigh the front end using a WDH vs just measuring. Most manufactures tell you to return the front of the vehicle to a % of the OEM ride height. If that has been achieved then why weigh it?

goducks10 wrote:
I still don't understand the need to weigh the front end using a WDH vs just measuring. Most manufactures tell you to return the front of the vehicle to a % of the OEM ride height. If that has been achieved then why weigh it?

Because to the uninformed, yet cautious driver/RVer this is good information. And it actually is, for training/experience purposes. Not everyone can “visualize” a load with any sort of accuracy.
At one point in my life I had no idea how to tow a trailer or what the potential issues were. For those at that stage of towing knowledge it is good visual proof of how the static weight distribution of everything happens when a trailer is hooked up.

goducks10 wrote:
I still don't understand the need to weigh the front end using a WDH vs just measuring. Most manufactures tell you to return the front of the vehicle to a % of the OEM ride height. If that has been achieved then why weigh it?

No RVer should every weigh their rig. Once they do they can no longer run the highways with no idea how much over the ratings they are. /sarcasm
If MT weight plus tongue weight plus what you load in TV exceeds GVWR of the vehicle, even if you crank the bars tight enough to get the front end ride height same as before hooked up you have no idea how overloaded you are until you weigh.

Weights are placeholders. Static.

Road forces are dynamic. Ever-changing. (Why TW & Payload mean next to nothing: it’s Axle ratings with tire/wheel ratings).

Acquiring the static numbers fits formula for what happens on-road.

Over time these may change. Normal wear & tear OR something’s truly off (defect or damage).

Having a numerical baseline acquired via scale readings shows:

1). The RANGE of adjustments for a given combination vehicle (from nearly empty and on up).
2). Side-to-side and across tandem axle tires the possibility of weight shift.

To TEST is what matters. Braking & steering are what matter in towing. The stupids think it’s about how fast they can ascend a grade (not lose speed). ONLY the downgrade matters, as that’s where most loss-of-control accidents occur from natural or man-made winds.

HANDLING is as much getting a grip on what it should be while solo (tire pressure and bed load securement) THEN some knowledge of what the combined rig feels like.

A combined rig is stable ONLY when under light to heavy throttle. Snapping a trailer back into compliance means BEST braking of both vehicles, and a distance from others full throttle plus MAXIMUM trailer braking is undertaken.

Replication of solo handling via WDH is to AVOID over-correction at the wheel (the pinpointed cause of loss-of-control). “Normal”.

The better the rig tracks (camber changes, ruts, and other surface deviations) the better the outcomes of direction changes not initiated by the driver.

The driver is the weak link. In a straight axle, high COG TV, he’s worsened his chsnces of trailer recovery as feedback from the rig is poor. (A couple of seconds and it’s over). If the trailer can shift the grip of the rear axle tires, Mario Andretti couldn’t save it.

Weigh #2 is to get an accurate read on TW. (Weight shift is bar tension as well as ball angle).

A pickup with a near-empty bed (in terms of weight) is a poor TV. It’s E-Z to lose rear traction in that scenario given road surface problems. And, where cars may slide or spin on losing rear traction, pickups will roll.

High COG trailers (slide-outs) on leaf spring axles are much the same. The design of each vehicle is fundamental as predictor (“skill” claims’ll get you laughed out of the room).

WDH spreads the forces each vehicle is creating across the length represented by the axle trio. Not just at the ball. Makes problems less so.

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