Tongue Weight

[Honda03842]

John,

There are many rules of thumb in life, most ne with our trailerver question the derivation. I guess I'm curious because I'm outside the bounds.

I was looking at a Forest River R=Pod last night and notice that they also have low tongue weights however they have an interesting tear drop shape. I wonder about the contribution of shape to towability.

Thanks for the info on ratio. This winter or certainly when I get home this spring I'll reduce further improve our wheelbase to ball ratio. It's simply a question of moving the ball closer to the body. My ball sits 8 inches from the hitch receiver, easy to improve and probably actually strengthens the connection.

This ratio is very important but in 9 years of RVing I have never heard it mentioned. Of course I had heard of getting the trailer load over the rear axle but no mention of the ratio.

I believe on this site I saw a picture of a fifth wheel being towed by a VW beetle where the fifth wheel connected to the center of the roof of the beetle, blacing the load exactly between the two axles.

Thanks for all your input. I'll be interested in this topic and whenever anyone finds out the reasoning behind 10% loading I'm ready to learn.

[kanyonkitty]

Originally Posted by EMD_Driver

Kitty never has that problem, but her driving habits are a wee bit different than mine..

Boy is that an UNDERSTATEMENT !!!!! :P :P :P

[Honda03842]

When we get to Florida shortening the overhang by at least three inches will be the first priority. It's a free enhancement in the proper direction.

I think reducing the overhang distance does two things.

First it reduces the lever arm acting on the tow vehicle when pushed sideways by sway.

Second it moves the tongue weight closer to the axle, always a smart improvement reducing the tipping action on the tow vehicle caused by tongue weight. Though we don't see any tipping, there must be some.

I think another magic factor with the Honda and our little Sunline is that the weight of the trailer is about 60% of the weight of the vehicle, compared to 100% or more for many tow vehicle/trailer combos (and even more for fifth wheels).

Even though our tow vehicle is light, it's not with respect to our trailer.

We're constantly approached by people who are surprised by our ability to tow our Sunline. Now I can better explain why the Honda works, of course along with the great lightweight design of our Sunline.

I'm continually approached by people wanting to buy it - I think the interest results from increasing fuel prices, a desire to return to simpler camping yet keeping the comfort of a trailer, and cutting out the complexity of bigger rigs.

With better hitch design another four inches could have been picked up moving us into the 35% range with no added cost to the hitch design.

Thanks for the tip. Hitch overhang is so important I'm now surprised its not mentioned more.

Of course reducing the overhang also allows for heavier tongue weights without having more efffect on the Honda.

Though I still don'tunderstand the 10% I am beginning to understand the TV/Trailer relationship better - thanks to all

[JohnB]

Originally Posted by Honda03842

When we get to Florida shortening the overhang by at least three inches will be the first priority. It's a free enhancement in the proper direction.

I think reducing the overhang distance does two things.

First it reduces the lever arm acting on the tow vehicle when pushed sideways by sway.

Second it moves the tongue weight closer to the axle, always a smart improvement reducing the tipping action on the tow vehicle caused by tongue weight. Though we don't see any tipping, there must be some.

Yes Norm you are correct. OK here are some numbers for you. I gave you this in 1 lb math so you can easily multiple it up for what ever tongue weight you have at the time.

You stated 104” WB and 44” over hang.

On 44” this comes out to: For every 1# of tongue weight, 1.42# is added to the TV rear axle and 0.42# is removed from the front axle.

Then you stated, 104 WB with reduced overhang from 44 to 41.

On 41” this comes out to: For every 1# of tongue weight, 1.39# is added to the TV rear axle and 0.39# is removed from the front axle.

So as you can see the 3” did buy you a “little” relief in axle loading in the TV rear and unloading in the TV front. If you still have your 160# tongue then that is 160 x 1.42 = 227.2 # added to rear axle and 160 x 0.42 = 67.2# removed from the front axle on 44” rear overhang.

And on 41” rear overhang, 160 x 1.39 = 222.4# added to the rear axle and 160 x 0.39 = 62.4# removed from the front axle.

Basically 3” buys you 4.8# less added to the rear axle and 4.8 # less removed from the front axle. Not a lot, but the math shows it does something.

Originally Posted by Honda03842

I think another magic factor with the Honda and our little Sunline is that the weight of the trailer is about 60% of the weight of the vehicle, compared to 100% or more for many tow vehicle/trailer combos (and even more for fifth wheels).

Even though our tow vehicle is light, it's not with respect to our trailer.

Yes having a TV out weigh the TT is a positive attribute. The more TV weight the better it resists the effects of the TT pushing on it. While mass of the TV alone is not cure all for every towing problem out there, it does help.

Originally Posted by Honda03842

With better hitch design another four inches could have been picked up moving us into the 35% range with no added cost to the hitch design.

Thanks for the tip. Hitch overhang is so important I'm now surprised its not mentioned more.

Of course reducing the overhang also allows for heavier tongue weights without having more efffect on the Honda.

Though I still don'tunderstand the 10% I am beginning to understand the TV/Trailer relationship better - thanks to all

H’mm now you said 4”, before your where mentioning 3”. If you can go from 44” to 40” that turns into 1.38# added to the rear axle and 0.38 removed from the front axle for every 1 lb of tongue weight.

A heads up when reducing rear overhang is the crunch factor. Meaning watch the TV fender does not crunch into the side of the camper. Before moving the hole in the hitch bar, slowly back into almost a jack knife while someone is watching the hitch area. Look at the TT to TV fender clearance. I would not shorten up the hitch bar if you are going to crunch the TV into the TT because of moving it in 2 to 3”. Remember you are only gaining 4.8# weight change with 3”

I’m actively working on getting you a better explanation on the 10% minimum tongue weight relationship. If you want to read a bunch of really high up math stuff, see this very good book I was pointed to. Trailering starts on page 75 to 96. Vehicle stability By Dean Karnopp

I’m working on breaking that down into easier to understand real life experiences that are easier to relate to. Stay tuned for more yet to come.

Hope this helps

John

[Honda03842]

Jon,

The Bounder windows are thermopane sliders (with condensation vents at the bottom. Every design has some kind of flaw.

[JohnB]

Norm

I am still working on getting you an explainable answer on the 10% tongue weight. I opened a post on RV.net on this and getting a factual answer is still in the making. The rule of thumb 10 to 15% is a good one, I use 13 to 15%, but there is more to the make up of the rule then just tongue weight. That is the hard part to dig up but I am getting closer.

See here, there are already some good links I found and they are in this post. The 10% min Tongue weight rule - Why? I must also admit, there are good responses and some that are down right, well, not very camper like. Just ignore them.

If you want to read on, here are a few links I already found or where linked to be by other camper friends. Some of these are really higher level math, but I will summarize and break this down once I sort it all out.

Vehicle stability By Dean Karnopp Start on page 75

Here is one from down under. Hopefully this link works. They state the reason for the 10% rule different then I have heard before. While not off base, they are not the total reason.
Tow ball Weight and Stability

And here is a study done in the UK on the effects of sway on a TT.
http://www.towingstabilitystudies.co...s-research.php

And they also now in Europe make a sway control braking system for the TT.
http://www.al-koatc.co.uk/index.htm

And here is one that has a lot of good stuff in it about tests done for the NHTSA back in 1979 on braking and trailer tongue weight and stability. Our Government dollars at work. It cost over $245K back in 1979.

http://www.edccorp.com/library/TechRefPdfs/EDC-1082.pdf

This much I can tell you, the pure weight of the tongue is only part of the equation. However it is the one us campers can better control once a TT is built. The test studies in the link above do show that the higher tongue weights do make a difference in damping down the sway effects of a TT being pulled on a conventional hitch. They tested 5, 10, 15 and 20% in some cases. They also talk about what the TV can hold up. So your 6% did not fair as well as the 10% bottom and higher was even better.


They however do not go into the exact reasons yet. I’m only on page 117 of the 154 but I skimmed to the end and did not see what I was after but there is a lot of good in there and by creditable sources.

The length from the front axle to the tow ball is a big part of the equation. The longer the better. However most TT’s are made all with the same kind of standard A frame setup from tow ball to header. Even across all kinds of brands, it is fairly common on medium and large TT’s to be in the 4 foot range from header to tow ball, yet weights and lengths of the campers are all different.

I’ll be back with more soon.

Hope this helps

John

[Honda03842]

Another input Toyota recommendations.

Typically, tongue weight should represent about 7 percent to 8 percent of
your GTWR. If tongue weight exceeds 10 to 15 percent of GTWR, you must use a weight-distributing hitch and sway-control system.

Why is tongue weight so important, you ask?

One is to facilitate braking. Too much weight at the rear of the trailer, or even neutral trailer balance, can actually raise the rear of the tow vehicle during heavy braking.

Too little tongue weight or too much weight in the rear of the trailer can cause trailer sway, a dangerous side-to-side undulating between the trailer and tow vehicle.

If you have spent any amount of time driving freeways and interstates, you have probably seen trailer sway before. That’s why 60 percent of the load should be forward of the axles, distributed evenly from side to side.
However, too much tongue weight can place too great a load at the back
of the tow vehicle, which can unload the front wheels, causing undesirable handling, decreased braking performance and too great a load on your particular class of hitch. Conversely, too much weight on the rear of the trailer can cause trailer sway

[Honda03842]

The UK stability studies were very interesting. I particularly liked the ball connection, complete with grease fiting. It seems that 6-8% is the number in Europe and keeping the weight near the trailer axle is important, true in our little Sunline.

I also thought it was interesting that they believe the spare tire should be positioned near the axle and not on the rear bumper.

Their recommendations seem to line up with Toyota

[Honda03842]

John

Thank you for all the great information. I scanned the government report and now have an improved view of why our set up seems to work.

One big factor is the ratio of the Tow Vehicle weight to the trailer weight. Our ratio is 4000/2200, about 1.9 to 1. This definitely increases stability, making it hard for the trailer to push the car.

[JohnB]

Norm

Now you are getting it. However I am not yet convinced the 6% is your ideal target.

I’m not done reading and trying to break this down yet. I have bumped into many other things as well dealing with tongue weight and braking.

That government study actually has 4 volumes to it. 448 pages of “stuff” I have made it thru it now have to compile it in simpler to explain lingo.

Yes, your TV being heavier then your TT is a large help. They gave a guide line of 2.1 times the size of TV to trailer for “unbraked” trailers. Your has brakes so that is not in the same area but yet you still have a high percent of TV mass to the TT mass.

I’ll be back soon with more to summarize this up. I learned a bunch of new stuff too, so thanks.

John

[Honda03842]

The UK report said the largest factor is speed, one thing we don't do is drive fast, never getting faster than 60 mph. As well as suggested we keep our tires near max pressure stiffening side walls in trailer and tow vehicle.

As well, a heavy tow vehicle and a good wheel base to axle/ball ratio.

Another factor is the Sunline itself, small wind profile, weight well over the axle, short and first order aerodynamically shaped.

I'm feeling like we're beginning to understand the whys.



i haven't weighed the tongue since we arrived, but the propane tank is now full and the weight is probale near to 8%.