How to determine optimum height of hitch? - Fiberglass RV


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Old 06-14-2019, 10:05 AM   #1
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Name: Bob
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How to determine optimum height of hitch?

As mentioned in a recent post to another thread, there are many factors other than trailer weight that can affect how a trailer pulls. I'd appreciate some insights into how to determine the best height to set my hitch (adjustable in 1" increments) so my 17.5 Bigfoot single axle trailer will have the least effect on my tow vehicle.

So far, I can think of three potential strategies -

-- determine at what hitch height the trailer is perfectly level when lowered onto the hitch and, then, adjust up or down from there.

-- go by some # pounds on the hitch relative to the loaded weight of the trailer.

-- resort to trial and error.
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Old 06-14-2019, 11:25 AM   #2
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It's pretty commonly accepted that hitch weight should be 10% of the total trailer weight. Then you need a tow vehicle which can handle that weight.

Typically that means an almost level trailer, slightly "nose down".

With your 17.5 I'm going to guess that means about 350lb tongue weight.

Too much tongue weight and you're maxing your payload limit, plus at the extreme you're slightly lifting the front end of the tow vehicle, making steering pretty dangerous. At the other end, with very, very little tongue weight, the trailer will be unstable and sort of "float" and wiggle around back there behind you.
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Old 06-14-2019, 01:03 PM   #3
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It's pretty commonly accepted that hitch weight should be 10% of the total trailer weight. Then you need a tow vehicle which can handle that weight.

Typically that means an almost level trailer, slightly "nose down".

With your 17.5 I'm going to guess that means about 350lb tongue weight.
I am towing with a 3/4 ton diesel pickup truck so handling the weight is no problem.
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Old 06-14-2019, 01:18 PM   #4
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Set up your hitch height so that the trailer is level when attached to the TV and all your gear and water are loaded, both in the trailer and in the TV.

I get about 2" of sag when I hook up, and have the trailer as close to level as possible in that condition. I'd rather have it slightly nose down, than up. Also, besides being stable, level allows us to simply stop at a rest area for the night and not have to do any leveling.

If you are selecting the drawbar drop to achieve this, just hook up with what you have and see how much correction is needed. So, yes, some trial and error is involved. You can also position heavy things, like cases of water or tool boxes to help with weight distribution in both the TV and the trailer. For instance, you might push the cases of water, and any jerry cans, all the way forward in the pickup bed, or place the water over the axle in the trailer.

If you get too much sag after loading up the gear and hooking up, you'll have to correct it with air bags, overload springs, or a weight distributing hitch. Two inches or so of sag should be fine, four, not so much. And you'll need to stay within the towing limits of the TV and the tongue weight limits of the TV. So again, trial and error begins to play into it, along with reading the owners manual for weight limits.

If you really want to know how much tongue weight you have, you could order a Sherline tongue scale, or rig up a bathroom scale with some 2X4s to adjust the leverage and pressure on the scale. You can also visit a construction materials yard to get the weight of the trailer, or just the weight on the wheels.

Approximately 10% of the trailer's gross, is the accepted normal tongue weight. This does not have to be exact. Don't try to lighten the tongue by putting weight at the back of the trailer. Or even worse, out behind the trailer's rear bumper in a rack, unless you are sure of what you are doing.

I tried several draw bars before I settled on the one I now use all the time. My truck sits about 2" down in the back when all geared up and connected, and the trailer is almost perfectly level.

With your heavy duty truck, you can be pretty casual about al of this, but try to get the trailer level. I'm towing with a Ram 3500 diesel SRW and it is very tolerant of varying tongue weights and trailer weights.
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Old 06-14-2019, 05:56 PM   #5
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Actually the accepted tongue weight is BETWEEN 10 AND 15 PERCENT for trailers over 2000#.
Here you go, Section 4 under "Safety".
https://www.purdue.edu/transportatio...s/van/tow.html
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Old 06-14-2019, 07:41 PM   #6
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Joe,

I'm sure you realize that there are many factors related to trailer stability. Arguing over a general number is a waste of time. The numbers recommended by Purdue University of 10-15% are general guidelines that compensate for other problems. Too much weight can also cause instability, as can weight distribution, and a bunch of other factors. Trailer height, track width to tongue length ratio, spring stiffness, tire pressure, speed, tow vehicle weight and rear overhang, trailer center of gravity, and tongue weight, are a few factors on a long list.

One member on here has probably towed more than most of us combined, for many years, and he runs 7% with zero problems. Mine, at just over 9% is the most stable trailer I've ever towed. Apparently, in Europe, 7% is close to the norm. We have some friends in Germany that tow here while on vacations every year. They wonder why we use so much tongue weight. And apparently, 4% is the minimum in England.

So, stability is the most important issue and tongue weight is just one way to try to get there if you have other problems, or are looking for a general rule to follow. An example would be to lengthen the tongue. This lowers the tongue weight, but increases the stability.

So, when suggesting that someone try for about 10% when setting up their trailer, I don't feel that they are being misled. Especially when the recommendations also include mass centralization near the axle, no rear added weight, keeping the trailer level or down in the front, and carrying heavy stuff in the front of the truck bed. And when that person has a heavy duty truck, and a light trailer, they don't have to be too exact when following general rules because there is so much inherent stability. It's the ones towing trailers that are heavier than the tow vehicle that make me nervous. And, of course, everyone should know how to quickly apply the trailer brakes, independently of the truck brakes, in case of an uncontrolled sway event.
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Old 06-14-2019, 07:52 PM   #7
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Arguing over a general number is a waste of time.

As is bring up European norms ( and Norm ).
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Old 06-14-2019, 08:08 PM   #8
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Originally Posted by Glenn Baglo View Post
As is bring up European norms ( and Norm ).
Why? Do the laws of physics change mid-atlantic?
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Old 06-14-2019, 08:43 PM   #9
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So, the assumption is that Europeans are correct and Americans are mislead?
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Old 06-15-2019, 05:38 AM   #10
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My 3000# loaded Casita with 425# tongue weight comes out to 14.1%

Cars are lighter in Europe.

Back in the 1960's I owned a Sprite 400 "Caravan" made in England and it didn't take much to start it swaying. Mine had the door on our curb side.
In the 1980's we bought a used Sprite Alpine.
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Old 06-15-2019, 07:27 AM   #11
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I agree there's no one right number, but it helps to have a general target to shoot for. When I first bought my Bigfoot and drove it from Canmore, AB back to Helena, MT, I didn't know any of this stuff. I had practically no tongue weight. I remember seeing the trailer back there, sort of gently floating around. Lucky for me Bigfoot trailers tend to tow really well and stable. It didn't cause any instability in my truck.

Whether my propane tanks are empty or full, or however I happen to have weight stacked in the trailer; no matter how loaded down my truck is, no matter how much air I have in my trucks air bags (which has a drastic effect on height, and so also trailer angle), my trailer pulls nice and straight and stable. That's not the case with every trailer.
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Old 06-15-2019, 09:56 AM   #12
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All of this is to counteract trailer sway. Weight distribution and geometry are factors. Other things that can aggravate trailer sway are a loose drawbar, the hitch ball too far back of the TV bumper, and jerky steering.
Make sure the ball is as tight to the bumper as possible. Add shims or an anti rattle device, or set screws to make the ball mount to receiver connection tight,
And, drive with a steady hand on the wheel.
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Old 06-23-2019, 08:06 AM   #13
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A properly set up tow rig will utilize the following equipment.

Weight distribution hitch.

Sway control bars.

Safety chains.

Electric trailer brakes and brake controller in tow vehicle.

The weight distribution hitch can adjust the height and level the entire combination of the tow vehicle and the trailer resulting in a perfect marriage between the tow vehicle and the trailer resulting in a rewarding towing experience.
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Old 06-23-2019, 08:14 AM   #14
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Is this true? If someone doesn't have a weight distribution hitch and sway control, they aren't properly set up?
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Old 06-23-2019, 08:54 AM   #15
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ZachO, If you are serious about towing safety then depending on the length and weight of your travel trailer the equipment I listed is required.

As you travel down the highway take the time to note the overwhelming majority of travel trailers are being towed with the equipment I listed in my post.

Your RV travels will be more enjoyable if you are driving a stable rig set up for both safety and stability.

I have been a RV Traveler since 1983 and covered most National Parks and all but a few states, New Brunswick and Quebec in Canada...wanted to tour
Nantucket but research revealed there are no Campgrounds or RV Parks on that island.

Happy Safe Camping !
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Old 06-23-2019, 10:24 AM   #16
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Is this true? If someone doesn't have a weight distribution hitch and sway control, they aren't properly set up?
I disagree that everyone must have a WDH and sway control bars to be "properly set up".
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Old 06-23-2019, 11:25 AM   #17
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I disagree that everyone must have a WDH and sway control bars to be "properly set up".
2X

The problem with generalizations is that they are generally wrong.
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Old 06-23-2019, 11:34 AM   #18
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ZachO

You have 1,706 posts, I'm wondering by asking such a question if you just don't understand or simply keeping the fires going
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Old 06-23-2019, 11:39 AM   #19
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Originally Posted by Joe Romas View Post
ZachO

You have 1,706 posts, I'm wondering by asking such a question if you just don't understand or simply keeping the fires going
It seems he was responding to Uplander's generalization.
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Old 06-23-2019, 12:23 PM   #20
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My Lil Hauley is 3000 weight and 300 tongue. NO WDH, NO sway bar and stable as the Rock of Gibraltar, even at 85 MPH. Dragging a box thru the air has lots of potential instability related issues, especially with a bunch of stuff sticking out of the top. All the corrective items mentioned here have merit, and maybe I missed it, keep the trailer center of gravity as low as possible. Test your stability by twitching the steering wheel at increasing speeds and note how the trailer responds. It should track back to center after a couple sways. Start with small twitches and don't increase speed or twitches if things feel unstable. It is good know how your rig handles when passed by a truck going 80 MPH. A work colleague of mine was called as an aerodynamics subject matter expert in a case where a trailer went unstable when passed by a truck resulting in a crash.
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