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Old 02-02-2014, 07:06 PM   #43
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mstephens,

This is just my opinion, but because of the fact you are setting up a sedan, I believe you are right about where you want to be with adding 200 pounds to the front axle.

Most people today concentrate on just restoring or getting close to restoring the unhitched weight to the front axle, but most people today are towing with truck and SUV's, which are actually designed to carry their payload over the rear axle. (we've had this discussion on here before, and I'm certainly not trying to get it as heated as it's been in the past)

However, unlike a truck, a sedan is designed to carry most of it's additional payload divided between the front seat, the back seat, and of course the trunk. But my point is, the sedan is designed for it's overall load to be biased farther to the front than is a truck. So, based on this, I think you are good.
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Old 02-02-2014, 07:44 PM   #44
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Great info folks. Thank you. FYI, both front and rear have a GAWR of 2810#. I am good on both as it stands.

I will of course try to check in with Andy on Monday. I feel 1000% better at this moment than I felt 4 hours ago when I thought I would have to find a way to add another 100# of WD! If more was needed, I just don't see how it would be gotten without a floor jack under the bars.

If the right answer lies between 100% restoration (2300#) and 200# over, then I can easily fine tune it, because tilting the head is pretty painless and can be fine tuned. I added exactly 60# with the last tilt adjustment.

Now then, I will clean up the pigtail, and the brake release and the chains, install the friction sway (Thanks Howie for the nice advice) and take it out for a run on the open road. So far, tooling around in town other aspects are AOK. Brakes are great, power is great, shifting is beautiful, transmission runs at the same temp as no TT. There's some vibration under heavy power. I think it is the cat converter underneath. I get a LOT of looks from people.

I want to thank you all for your patience and your advice!
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Old 02-02-2014, 08:47 PM   #45
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If the right answer lies between 100% restoration (2300#) and 200# over, then I can easily fine tune it, because tilting the head is pretty painless and can be fine tuned. I added exactly 60# with the last tilt adjustment.
Your scales numbers indicate a tongue weight of approximately 1040#.
The load removed from the front axle when hitched with no WD applied would have been about 450#.
By loading the front axle to 200# in excess of the unhitched load, you transferred about 650# to the front axle for a FALR of 144%.
Approximately 250# was transferred to the trailer axles.

IMO, you should have a FALR of no more than 100% -- probably less.
However, I'm guessing that Andrew T will tell you more than 100% is okay.

If you do decide on 100% or more, I recommend you be cognizant of the potential for oversteer.

Ron
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Old 02-02-2014, 10:25 PM   #46
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Oversteer? That means the backend breaking loose first, right? I always thought that wss associted with cars having a heavy rear.

There seems to be a strong feeling for 100% FALR. Looks as though I have gone too far.
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Old 02-02-2014, 10:32 PM   #47
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A heavy axle will grab more, in general terms, until things go way out of the norm.

I gotta say, you have seriously cranked some weight to the nose!
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Old 02-03-2014, 06:34 AM   #48
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What we used for years (decades) was known as the one-third rule that the distribution was TW divided and distributed Steer - Drive - Trailer (with anything additional, by about 10%, on the Drive Axle) with adjustments to suit per specific rig. Keeping wheel/tire/axle limits in mind, always. One might creep up on FALR (a more modern term) and one might go over (as do 5'er hitches, often 50 to 150-lbs past FALR; but this is a smaller percentage of tongue weight and hitch effects are different, etc).

Oversteer is a concern for any articulated vehicle, not just the recreational traveler. The top-heavy bulk trailers (Class 8) I run for work can certainly get the adrenaline flowing with some problems of surface traction vs. speed, road, traffic, etc.

Experimentation takes a few miles, usually. Using numbers -- from TV tire pressures via scale readings as well as TW distribution -- learning to know how things should feel might take the most time. Definitions of words used is, I'd recommend, via Fred Puhns' basic book on vehicle dynamics (to avoid misunderstandings in discussion).

But the vehicle that is not CG-compromised is already a better candidate for use as stable tow vehicle. The forces that'll roll over a pickup are pretty much cause to a spin-out in one of the better cars of today. The perennial difficulty of oversteer is the inability of the driver to correct for it. Any driver. We're looking to find a balance twixt under & over steer, and favor steering response close-as-possible to solo as the ideal. "Just enough WD", in other words.

Axle/wheel/tire limits describe the envelope, whether we speak of the rigs we set up around here or in commercial use of 1T pickups where "ratings" are/were exceeded by 10k pounds or more (for a few hundred thousand miles) with gooseneck hitch trailers. Thus, the importance of weighing wheel-by-wheel. We'd want to know those loads, not just axle-by-axle, for the complete picture. The mechanical baseline.

Be patient. The rig is a known quantity, and the details will sort themselves before too long. Your determination is admirable.

.
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Old 02-03-2014, 10:00 AM   #49
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Oversteer? That means the backend breaking loose first, right? I always thought that wss associted with cars having a heavy rear.
I attempted to explain, in this post and this post, why/how too much load transfer to the front axle might cause oversteer .

However, I think HiHoAgRV has a better explanation:

"A heavy axle will grab more, in general terms, until things go way out of the norm."

Ron
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Old 02-03-2014, 10:12 AM   #50
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The car alone was 2300F/2180R = 51% front.

With my current level of WD I have: 2500F/2740R = 48% front.
With 2500lbs on the front axle, and 2740lbs on the rear axle, you are not going to have an oversteer problem, IMHO.
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Old 02-03-2014, 06:24 PM   #51
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Monday

I started by backing off on the head tilt to reduce the amount of WD. I got info from Andy about his 300, and he gave me wheel well measurements to shoot for. The hitch instructions also refer to WW measure and that's what I did.

Starting with no TT

Front = 30-3/4
Rear = 31 (with 70# in shocks)

Add the TT with no WD

Front = 32
Rear = 28

Add the WD back in

Front 30-1/4 now down 1/2" from start
Rear 29-1/2 now down 1-1/2 from start

It requires a reasonable amount of jacking up to get the chains on. Not dramatic, but more than the 3" quoted in the instruction book for the hitch.

Out normal hitchup is that when I back under the coupler, Paula drops the trailer down and latches. Then I get out and we raise the car with the jack to do the WD. So naturally, we have never seen what happens if you keep dropping the trailer on the car and remove the jack foot. WHOA! We got the jack stem all the way up into the shaft and it was sitting on the foot! and the car was nearly on the pavement. So, now I see that's the true "no WD condition."

Anyway, we did not go to scales yet. I mounted my Camco friction anti-sway bar, adjusted tire pressures per Steve H. recommendation, and we took another test drive on the freeway for 5 miles. Pretty good. The steering had a definite constant slight pull to the right. And there was a tad bit of wander. Not much, but some. I took it up to 67MPH. Our normal max is 59MPH. No sway that I could see or feel.

The sway adjust is crude. They say to start with the factory preset, but that's not even possible, because to mount this, you have to remove the adjustment screw! I am not sure of what the symptoms would be of "too tight?"

I'd sort of like to be able to get the rear to 30". A 1" drop with WD seems somehow the right target. I will make the adjustment tomorrow and do another scale read. I hope it is close to 100% FALR with a 30" rear wheel well measures. That would seem pretty good I think.
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Old 02-03-2014, 06:51 PM   #52
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The friction sway control is a long way from being very "precise", but when I used them my method for setting the amount of friction, or how tight to adjust it, was to tighten until it felt like it didn't want to straighten out all the way after a turn at slow speed, then reduce until it did. Yes, not very scientific either, but it worked for me.
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Old 02-03-2014, 06:52 PM   #53
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I got info from Andy about his 300, and he gave me wheel well measurements to shoot for. The hitch instructions also refer to WW measure and that's what I did.
Can you tell us what WW measurements Andy said to shoot for?

Quote:
---The sway adjust is crude. They say to start with the factory preset, but that's not even possible, because to mount this, you have to remove the adjustment screw! I am not sure of what the symptoms would be of "too tight?"
What are you calling the "adjustment screw"?

Usually there is a bolt with a one-sided handle. This bolt is used as an "on-off" control for the friction force.
A separate screw which requires a screw driver is used to adjust the magnitude of the friction force which is applied when the control handle is tightened "on".
As one engineer to another -- did you read all of the instructions?
I know I usually don't.

One symptom of "too tight" is if you have to consciously steer the car back to straight ahead after turning a corner or making a lane change -- as opposed to letting the front wheel alignment return the steering to straight ahead.

Ron
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Old 02-03-2014, 07:16 PM   #54
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With 2500lbs on the front axle, and 2740lbs on the rear axle, you are not going to have an oversteer problem, IMHO.
I would agree if all of the 2500# on the front axle resulted from the mass of the tow vehicle and the location of its center of gravity.
However, about 25% of that 2500# is not a result of TV mass and CG location.

The 625# which was exerted on the front axle via application of WD is not a result of additional TV mass.
That 625# is a result of torque from the WDH being translated to a downward force on the front axle via leverage.

The extra 625# of tire load means additional lateral tire force, but there is no corresponding TV mass to absorb the effects of the additional force.
This causes the TV to "steer" more than the steering wheel angle is requesting.

There is delicate balance among front axle lateral force, rear axle lateral force, and CG location.
The imposition of a force, without corresponding mass, on the front axle can upset the balance.

Ron
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Old 02-03-2014, 07:31 PM   #55
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It's only 200 pounds more than the car weighs without the trailer attached, and there's almost 600 pounds added to the rear axle of the car.

I don't think it would be a problem at all.
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Old 02-03-2014, 09:02 PM   #56
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It's only 200 pounds more than the car weighs without the trailer attached, and there's almost 600 pounds added to the rear axle of the car.

I don't think it would be a problem at all.
The problem is -- the 600# added to the rear axle results from the addition of a effective mass equivalent of about 1000# added to the ball at a point about 4' behind the TV's rear axle.
That also contributes to oversteer, in addition to the effects of load distribution to the front axle.

Towing factors which contribute to oversteer are quantified and discussed in Effects of Trailer Hookup Practices on Passenger Car Handling and Braking. The abstract states:

"---Abrupt reductions in understeer were observed which increased the tendency for jackknife---".

"Reduction in understeer" refers to a decrease in the "understeer gradient", and is the same as saying "increase toward oversteer".

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