Sunline RV Forum
Sunline User Photos

Go Back   Sunline Coach Owner's Club > Technical Forums > Towing and Tow Vehicles
Click Here to Login

Join Sunline Club Forums Today


Reply
 
Thread Tools Search this Thread Display Modes
Old 11-08-2009, 02:40 PM   #1
Senior Member
 
Join Date: Jun 2007
Location: New Hampshire
Posts: 1,025
SUN #292
Honda03842 is an unknown quantity at this point
Tongue Weight

We're on the road again. Tonight we're in Lum Pond State Park in Deleware, a rather pleasant park, empty tonight on a warm evening.

This summer we changed the balance of our trailer by adding two solar panels to the rear of the roof iof our little trailer. This 40 pounds seems to have reduced the tongue weight to 160 pounds on our 2400 pound fully load trailer.

This is much below the 10% we used to have. However it towed extremely well for the last two days, some 500 miles from NH. It seems I do not understand tongue weight and am looking for understanding.
__________________

__________________
Norm and Ginny Milliard
1982 Sunline 15.5 SB
2004 Honda CRV 4 cyl, manual
Honda03842 is offline   Reply With Quote
Old 11-08-2009, 08:08 PM   #2
Moderator
 
JohnB's Avatar
 
Join Date: Nov 2006
Location: Ohio
Posts: 9,901
SUN #89
JohnB is on a distinguished road
Hi Norm

Am I understanding your numbers correctly, your TT weighs 2,400# total (tongue weight plus axle weight) and the tongue is 160#?

If so, then 160/2400 = 6.7% tongue weight per GVW. If I understand your numbers from your post correctly, as a camper friend Im expressing caution with that balance of the TT. It is good that the last 2 days have been well for you. Great. But.

Let me ask if I can how you define well and what conditions the last 2 days presented to you?

1. Did you have to do any steering corrections for a wiggling TT?

2. Did you have to use the brake controller manual button at all, even once to help pull the TT back in line? I thought from past posts you stated you use it often and Im just asking so we can make sure we are all grounded to what well means.

3. Has there been much semi traffic?

4. What towing speed do you travel?

5. What type of anti sway device are you using? A friction sway bar?

6. Has there been any wind and if so any idea on how hard it was blowing? Here are some ways to determine winds speed in a general sense.

Smoke rises straight up = 0 MPH
Smoke drifts = 1 3 MPH
Leaves ruffle/ flags stir = 4 7 MPH
Leaves and twigs move = 8 12 MPH
Branches move and flags flap = 13 18 MPH
Small trees sway/flags ripple = 19 24 MPH
Large branches move/ flags beat = 25 - 31 MPH
Whole trees move/ flags extend = 32 38 MPH

I did not create those rules of thumb, they are straight out of the Boy Scout Field book, page 153, of the 3rd edition. The one that I remember easy is, Flags Fly Straight and your in a 30 mph wind or greater. I just look around at peoples houses/business and Im sure to find one to gage what wind Im in when towing.

Now to what I think you are asking.

Quote:
Originally Posted by Honda03842

This is much below the 10% we used to have. However it towed extremely well for the last two days, some 500 miles from NH. It seems I do not understand tongue weight and am looking for understanding.
Here are a few articles on controlling sway. This one is off the Sunline site. Better read it quick before the site goes away again. Bill Estes does a good job of breaking it down to understandable info.
http://www.sunlinerv.com/index.php/s...trolling_sway/

And here is one more from the company that sells the tongue weight scale I have. There are many links off this page.
http://www.sherline.com/lm.htm

And here is a post I did on pictures of Carvans in Germany a few years ago. There they all have small TTs pulled by very small cars. However they also limit the speed people can tow at. In some EU countries it can be as low as 40mph as I was told. And they preach proper tongue weight even on television during the holiday season. Yes, they actually have nightly broadcasts on how to balance your Caravan.
TT's and Hitches in Germany - Pic's


OK now from my own words on tongue weight and why having it helps create a stable towing TT.

1st you have some things going for you that are different then many of use here with larger campers and TVs. They are a plus in your case, but I would not use them as my primary anti sway control program.

Your TT is only 7 foot wide and it is lower to the ground then many of ours. I could not find how tall your 82, 15.5 SB is. How tall is it, ground to roof?

Many of ours are 8 feet wide and 8 feet ground to roof or higher. These larger campers have more frontal area and the wind affects the fronts different in a negative sense then a smaller width TT or cargo trailer.

Rear overhang. Many larger SUVs, PUs even ton and larger vans can have a rear overhang of 56. Rear overhang is the distance from the center of the rear axle to the center of the tow ball. The longer this distance the more affect sway can have on a TV. Your smaller Honda may have a lot less rear overhang which is a very positive thing in less sway effects. Do you know your rear overhang?

OK now to tongue weight and TT balance. Tongue weight or hitch weight is the % of TT gross vehicle weight that is on the tow ball. The rest of the TT GVW is carried by the TT axles.

Think of it this way. The axles are like a teeter tooter fulcrum. If you have 0% tongue weight, then the TT is perfectly balanced on the axles. As you pull a TT with 0 % tongue weight the TV has no added weight to it. However the TT will not track well. Any instability in driving conditions can push the front or back of the TT left or right or pop it up or drop it down. That is because it is literally teeter tottering on the axles in many directions at once.

With a 0 % tongue weight TT the center of gravity of the TT is exactly on the axle center. Weight on both sides of the axle is split 50/50. Now move the axles on the TT so the center of gravity moves 10% to the rear of the TT. This means 40% of the weight is behind the axles and 60% of the weight is forward of the axles. Now the tongue will drop to the ground if unsupported as the front is heavier.

As you pull the TT with 60% of the weight forward of the axles, or 10% tongue weight, the TT wants to track straighter when forces act upon it. At 0% tongue weight it took little effort to push the front or back of the TT left to right. It spun on the axles which was right at the center of gravity. When you are 10% tongue, it takes a lot more force to push the TT. At 15% tongue, it even takes that much more force to push it left to right once it is tracking straight ahead.

OK now lets put the axle at the back of the TT. Right at the rear wall. Now the axles are only carrying 50% of the TT weight. The tongue is carrying the other 50% of the TT weight. This is even a more stabling towing setup when pulling the TT forward. It resists side forces greatly. This is sort of like a semi trailer as those wheels are in the back of the trailer. While this is about as stable as you can get with only 1 sets of axles in a group, it also means the TV has to hold up 50% tongue weight and the TT frame has to take that long span to the front. This becomes a problem on how to hold up that much tongue weight so it is not used in TTs. However they do make gooseneck horse trailers this way.

It has been found that 10% tongue weight is a minimum guide for TTs. Pending the TT and the TV, this might get by with no issues until the wrong set of conditions comes that over come that 10%. Or a wrong gear move in the TT dropping the tongue weight to 9 or 8%. In some cases you can drop 1% tongue weigth by an empty LP tank.

By going to 13% or 15% it even a more stable pulling TT and gains more freedom in TT loading in case you move an object. 20% can be even better. However the 15 and 20% comes with higher tongue weight that the TV may not be able to handle. So the recommendation is to only drop down to the 13% area. 12% is a better bottom end, Remember the empty LP tank.

When you go under the 10% target the stability of tracking straight is affected. Now it may or may not be seen until the wrong set of conditions comes your way. Your short rear over hang and narrower TT are helping, but they only can help so much. When ever you tow with a TV and hitch that has a lot of rear overhang, you should get all the benefits you can from a stable towing TT and that first starts with higher levels of tongue weight.

I know it may seem that right now with 6.7% tongue weight you feel your doing OK, however it is not optimum when adverse towing conditions come your way. Higher tongue weights will help prevent a TT oscillation from starting and once started you will fair a better chance of dampening it down with 13% then 6.7 % .

Another point to keep in mind, while 13% tongue weight is good TT balance, the TV has to be able to hold it up. Overloading the rear axle on the TV to get to 13% tongue weight is not a solution either. Both the TV and TT need to be optimized.

Hope this helps and I really want to encourage you to get your tongue weight back up.

John
__________________

__________________
Current Sunlines: 2004 T310SR, 2004 T1950, 2004 T2475, 2007 T2499
Prior Sunlines: 2004 T2499 - Fern Blue
2005 Ford F350 Lariat, 6.8L V10 W/ 4.10 rear axle, CC, Short Bed, SRW. Reese HP trunnion bar hitch W/ HP DC

Google Custom Search For Sunline Owners Club
JohnB is offline   Reply With Quote
Old 11-09-2009, 05:00 AM   #3
Senior Member
 
Join Date: Jun 2007
Location: New Hampshire
Posts: 1,025
SUN #292
Honda03842 is an unknown quantity at this point
thank you

John,

Thank you for the great response. I'll study it tonight.

As to speed we drive about 55, occasionally at 60 mph. I had no occasions to use the trailer's electric brakes. In the past when the weight was closer to 10% we might hit it a time or two in two hundred miles. When I did hit it the sway was really slight.

We avoid Interstates when we can though when we're leaving the Northeast it's mostly Interstates with in this case weekend truck traffic, though semis seem to not affect us.

Most sway events, an their rare, occur in weird situations like down hill runs where it's like the trailer is running faster than that the tow vehicle.

Thanks again I will carefully read this post.
__________________
Norm and Ginny Milliard
1982 Sunline 15.5 SB
2004 Honda CRV 4 cyl, manual
Honda03842 is offline   Reply With Quote
Old 11-09-2009, 10:43 AM   #4
Senior Member
 
henryj's Avatar
 
Join Date: May 2008
Location: Ontario
Posts: 635
SUN #597
henryj
Downhill braking

Norm,
Do I recall correctly you have a manual transmission? It seems to me the effect of engine braking on a downhill stretch could indeed have the tt "running faster" than the tv. In fact, if engine braking is all you need on most downhills you have the effect of braking the tv with no brakes on the tt.

I rarely brake from high speed on a downhill stretch as a hill needs to be pretty steep to overpower the big "air brake" I'm towing So, with an automatic, I'm just coasting down most hills and the trailer's air resistance provides all the braking it needs. If I do need a lower gear for engine braking, I'll brake first to slow down some and then select the lower gear, or better yet, get the lower gear before I even start down hill. Of course it helps that the 2499, with its rearward axles and high tw plus my long wheelbase crew cab, is an inherently stable rig to begin with. I agree with John's comments that you don't have an inherently stable combination and should try to get the tw up.

If you're running downhill in od, you might not have that much engine braking even with a manual. But selecting a lower gear while speeding downhill is not a good idea with either manual or automatic.

Henry
__________________
2015 Silverado 1500 NHT
2014 Arctic Fox 22G
2005 Sunline T-2499
henryj is offline   Reply With Quote
Old 11-09-2009, 10:51 AM   #5
Moderator
 
Sunline Fan's Avatar
 
Join Date: Dec 2006
Location: Michigan
Posts: 5,971
SUN #123
Sunline Fan is an unknown quantity at this point
Re: Downhill braking

Quote:
Originally Posted by henryj
If you're running downhill in od, you might not have that much engine braking
With about 1000 miles of experience with Ford's Tow/Haul mode, I'm thinking they could have done a little better job.

It is engaged just like shutting off OD, in fact there is no OD shutoff, Tow/Haul is it. It will run in OD with Tow/Haul on.

My biggest disappointment with Tow/Haul is the braking. Granted I haven't had the opportunity to attempt a BIG hill (such as coming to the Buttonwood M&G), but so far in order to get any braking, you really have to go on the brakes to get it to shift down any significant amount to feel any engine braking. I've yet to read any manual, but based on what I've read, I tried just tapping momentarily on the brake pedal before going down a hill and it does almost nothing.

Jon
__________________
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9467.8 (as of 5/26/19)
1997 T-2653 Blue Denim, #5471
1979 12 1/2' MC, Beige & Avocado, #4639
Past Sunlines: '97 T-2653 #5089, '94 T-2251, '86 T-1550, '94 T-2363, '98 T-270SR
Sunline Fan is offline   Reply With Quote
Old 11-09-2009, 02:39 PM   #6
Moderator
 
EMD_Driver's Avatar
 
Join Date: Jul 2009
Location: West Virginia
Posts: 2,039
SUN #897
EMD_Driver is an unknown quantity at this point
Send a message via MSN to EMD_Driver Send a message via Yahoo to EMD_Driver
Kitty's truck has the tow/haul mode on it and my experience with it is a bit different. It does tend to downshift itself quite a bit and not always at the best times. I almost think the rig is going to jack knife sometimes. Kitty never has that problem, but her driving habits are a wee bit different than mine..
__________________
Gary
SunlineClub Custom Google Search

2007 Peterson Excel Limited 30RKE
2014 Ford F350XLT SRW Crew Cab, Long bed 6.7PSD

EMD_Driver is offline   Reply With Quote
Old 11-09-2009, 04:57 PM   #7
Senior Member
 
Join Date: Jun 2007
Location: New Hampshire
Posts: 1,025
SUN #292
Honda03842 is an unknown quantity at this point
John's post and subsequent posts have given me a lot to think about. I did download the SunlineRV explanation and will have it for any one in the future.

I fully admit t not understanding optimum hitch weight though I have read many articles at least from the prospective of the physics.

There does seem to be universal agreement that it should be at least 10%; I just don't YET understand why.

As to noticing a little occasional sway and usually on the downhill sections, what was suggested is definitely possible, our manual transmission provides tow vehicle engine braking and any off angle by the trailer drives sway. Definitely possible.

We are careful downhill drivers, again because of experiences with our Bounder. Most motorhomes are really under braked. As a result experience has taught us to downshift on 'speed up down hills'. We try to hold speed gains on down hills to no more than 10 miles an hour. Generally we down shift when we see trouble coming. We have never gone 65 while towing our trailer.

We do have an anti-sway friction bar, since we've always had it I can't say how it tows without it.

I will say that most of the weight of the Sunline is over the wheels, water tank, black tank, gray tank and all appliances are either over the axle or close to it.

One advantage of the CRV is there is little overhang, from the axle to the rear bumper, 3 feet or less plus about 8 of ball support.

At WhatTowCar.com, a European site on the user reviews, it's pretty clear that people drive towing 80 to 95% of car weight and drive at speed and get very good mileage. It seems that the better engines and transmissions go to Europe, virtually every brand has a diesel version and six speed transmission.

The above site has very good information about the ability of various vehicles, particularly non-American, though it does have some American vehicles.

I have driven in many European countries and speeds do vary. Some roads in Ireland can not be driven at high speeds due to their nature while on the Autobahn I was once driving over 100 and passed like I was stopped. Just amazing.

I would estimate that the roof is 7 feet high. Another factor is the front of the trailer is sloped for about 1/3rd of it's height, this must put a downward force on the front of the trailer. I wonder how many pounds that amounts to?

Please understand I am trying to work this thru my head and not meant to be in opposition to any idea.

I agree that the trailer is like a see saw, more so than the multi axle trailers, However since the ball, discounting the sway bar is a simple low friction pivot, any side forces cause sway, no matter the weight on the ball. In my narrow view more weight on the ball does is increase rotational friction at the ball. It is hard to imagine that the level of friction there does much to help prevent sway. If that were the case when driving in a straight line you could just tighten the ball to it's cap to prevent sway.

Of course I would not mind if the tongue weight were greater. I had intended to add an additional battery after putting the solar panels on the roof. When I decided to build a trailer I decided to wait on the battery.

Also our propane tank is low, filling it will add another 20 pounds.

As to wind, we try not to drive on windy days. When we drove our Bounder where the wheels are at 60%, high side winds tended to want to spin the rig around the rear wheels. We were always very careful with winds. The trailer seems to be pretty balanced with respect to side winds.

We have been to Newfoundland and on the west coast there's a section called Wreckhouse where the winds reach hurricane force come through a cut in the mountains. On our last trip we passed two semis on their sides, blown over that night. Wreckhouse got it's name because a locomotive engine got blown over there once. Respect the strong.

Our TV is generally lightly loaded, just the two of us and a couple of chairs. The Honda seems to be easily able to manage the tongue weight. Last year with a heavier tongue weight the Honda did so without problem.

As to tire pressure, our Goodyear Marathons are rated for 50 lbs max and we run them at 45. Our TV tires are rated at 44 lb max and we run them at 39 lbs. The Honda, not surprisingly sits very flat when towing and never feels light in the front. Interestingly in all our towing, including the 1000 miles of Trans Labrador highway gravel I do not recall the 4 wheel drive kicking in once.

When the trailer sways, the tires must scrub sideways. With virtually all the weight on the tires the side forces felt between the rubber and the road must be highest when no weight is carried by the car.

If the wheels were at the rear with 50% of the weight on the tires and 50% on the car the side resisting sway forces of the tires would only be half what they are now because those forces are proportional to the weight on them.

Sway occurs when a side force pushes the trailer off the trailer/tow vehicle tracking line. If the Tow Vehicle slows down without the trailer simultaneously slowing down, the momentum of the trailer unless it is fully dead on to the tow vehicle has to push the TV one way or the other.

Since most sway events I can remember occurred on downhills, I suspect this is my problem. I simply do not see how more weight on the TV helps this situation. If I assume there is 20% weight on the TV and I stop the car quickly, it seems the trailer has to swing to dissipate it's energy (barring an anti sway bar and then it's a question of degree and speed. )

I fully admit to not understanding how tongue weight works unless it's the effect of ball to tongue friction. Comparing a freshly lubned ball and a non lubbed, higher friction, ball may go towards explaning friction at the ball.

Always something to learn, willing but slow,
__________________
Norm and Ginny Milliard
1982 Sunline 15.5 SB
2004 Honda CRV 4 cyl, manual
Honda03842 is offline   Reply With Quote
Old 11-09-2009, 06:08 PM   #8
Senior Member
 
Join Date: Jun 2007
Location: New Hampshire
Posts: 1,025
SUN #292
Honda03842 is an unknown quantity at this point
continuing to think about it...

Small changes in a lightweight trailer like ours can have dramatic affects on the percentage of weight on the tongue.

A mere 40 pounds on the rear of the trailer represents 2% change at the tongue. Another 20 pounds of propane represents another 1%. These two together put me back to 10%.
__________________
Norm and Ginny Milliard
1982 Sunline 15.5 SB
2004 Honda CRV 4 cyl, manual
Honda03842 is offline   Reply With Quote
Old 11-09-2009, 10:00 PM   #9
Moderator
 
JohnB's Avatar
 
Join Date: Nov 2006
Location: Ohio
Posts: 9,901
SUN #89
JohnB is on a distinguished road
Hi Norm

First off, I understand your not opposing good tongue weight and TT balance, your trying to understand why. Ill try in words or pictures on how to do this. SOC is a very good site to talk about these kinds of things openly so they can discussed and different opinions expressed in a camper like manner.

I have been looking for you trying to find in print a better explanation of why the heavier tongue weight make a more stable towing trailer. But I have not found yet what I am looking for. So Im still digging on how to explain this is a way that is easier to understand. Actually I can show it with a model trailer easier then explain it, but give me a day or so and Ill come up with what Im after.

In digging tonight, here is one site that had good info and even pointed back to the Sunline site...

http://sierranevadaairstreams.org/ow...ding/sway.html

Now to some of your thoughts and questions

Quote:
Originally Posted by Honda03842

Snip....

John's post and subsequent posts have given me a lot to think about.

I fully admit to not understanding optimum hitch weight though I have read many articles at least from the prospective of the physics.

There does seem to be universal agreement that it should be at least 10%; I just don't YET understand why.

As to noticing a little occasional sway and usually on the downhill sections, what was suggested is definitely possible, our manual transmission provides tow vehicle engine braking and any off angle by the trailer drives sway. Definitely possible.

One advantage of the CRV is there is little overhang, from the axle to the rear bumper, 3 feet or less plus about 8 of ball support.
Norm, this may help. Please measure from the center of the rear axle to the tow ball. Mark it out on the ground then measure with a tape. Try to be as accurate as possible. And what is the CRV wheel base, center of front tire to center of rear tire? I can use those numbers to help show leverage effects. There is a ratio that should not be exceeded.

Quote:
Originally Posted by Honda03842

Snip

I would estimate that the roof is 7 feet high. Another factor is the front of the trailer is sloped for about 1/3rd of it's height, this must put a downward force on the front of the trailer. I wonder how many pounds that amounts to?

Please understand I am trying to work this thru my head and not meant to be in opposition to any idea.

I agree that the trailer is like a see saw, more so than the multi axle trailers, However since the ball, discounting the sway bar is a simple low friction pivot, any side forces cause sway, no matter the weight on the ball. In my narrow view more weight on the ball does is increase rotational friction at the ball. It is hard to imagine that the level of friction there does much to help prevent sway. If that were the case when driving in a straight line you could just tighten the ball to it's cap to prevent sway.
The slope of the front of the Sunline helps the brick effect so to speak. It does not put more force downward a whole lot. It actually helps get rid of blunt wind force straight on or at and anlge to the front. The air can go up and over verses beating into the blunt from end and pushing the TT. And if it is beating on and angle, the blunt front will be affected and more unstable then a sloped front that deflects it off.

The extra weight on the tow ball, well no not really. The TT does not track straighter because on increased friction on the ball. The friction on the tow ball is not what makes the TT track straight. And you right, when you grease the ball there is less friction there. And yes, always grease the ball.

Side forces by wind do not always create sway. They are always forces but only turn into sway when the stability of the TT and TV can no longer resist them. I know a play on words but a lot to them.

Quote:
Originally Posted by Honda03842

Snip

When the trailer sways, the tires must scrub sideways. With virtually all the weight on the tires the side forces felt between the rubber and the road must be highest when no weight is carried by the car.

If the wheels were at the rear with 50% of the weight on the tires and 50% on the car the side resisting sway forces of the tires would only be half what they are now because those forces are proportional to the weight on them.
There are a few things right and not so right with what you have said. Yes, the heavier the weight on the tires, the higher the friction is between the rubber and the road. That is right out of the laws of friction.

Lets break down a side force of a wind gust on a TT on the drivers side. Say a 30 mph wind gust hits the driver side of the TT at an angle to the front of the TT. The front of the TT gets a big push of force. What happens next depends on a number of things. Since the force is pushing on the front part of the TT it wants to push the ball coupler towards the passenger side. Now also say your friction sway bar is real tight. The connection between the TT and TV is more rigid, however the TV rear and front tires plays into this too. The rubber may never leave the road just yet but the tire can flex in the side walls.

The front of the TV could feel like it is kicking to the driver side (left) because the friction bar could not hold all the force and the truck pivoted on the rear axle and or the rear tires flexed too in the side walls. Front went left and TV rear went right. The driver now feels the truck front kick to the driver side so they steer right. Now the tow ball goes in the opposite direction and up into the wind and the wind pushes hard again and pushes the TT ball coupler back once again to the passenger side. We have now produced 1 oscillation from right to left and back right of TT tow ball. The tires never left the pavement yet.

If this keeps up and builds strong in each oscillation, a full blow sway effect is underway and now the TT and TV tires can start to break free from the pavement if the swing gets larger enough.

If the driver never tried to correct the problem, well he might be heading to the left into oncoming traffic. However many times the drivers over corrects and can agravate the sway oscillations even worse. This is why they say try not to steer very much, go straight ahead when sway starts as steering too much aggravates the sway. And by applying the TT brake controller only while going straight ahead, pulls the TT and TV connection tight and helps dampen out the sway oscillation.


Quote:
Originally Posted by Honda03842

Sway occurs when a side force pushes the trailer off the trailer/tow vehicle tracking line. If the Tow Vehicle slows down without the trailer simultaneously slowing down, the momentum of the trailer unless it is fully dead on to the tow vehicle has to push the TV one way or the other.

Since most sway events I can remember occurred on downhills, I suspect this is my problem. I simply do not see how more weight on the TV helps this situation. If I assume there is 20% weight on the TV and I stop the car quickly, it seems the trailer has to swing to dissipate it's energy (barring an anti sway bar and then it's a question of degree and speed. )

I fully admit to not understanding how tongue weight works unless it's the effect of ball to tongue friction. Comparing a freshly lubned ball and a non lubbed, higher friction, ball may go towards explaning friction at the ball.

Always something to learn, willing but slow,
Norm when you said Sway occurs when a side force pushes the trailer off the trailer/tow vehicle tracking line. Yes, this is true and the points where higher tongue weights help the TT track straighter without fish tailing. It's just the why that is eluding you right now.

It is not so much that the TV has more weight, however it does help plant the rear tires more stable to the concrete, it is that the TT will track straighter with higher tongue weights even in no wind.

This is where a show and tell model comes in handy. I had one at the Buttonwood M & G this year to show and tell. If a trailer has a heavier tongue it will naturally pull straighter then with a light tongue with no wind. Wind just aggravates the problem.

See if you can make yourself a mocked up model TT. All you need is a piece of wood say 1 foot long. Then hang a 4 inch long tongue on it. Then put a round object in the exact center of gravity. A round ball point pen for an axle will help in case you do not have model tires and an axle. Since the axle is on the center of gravity the TT is exactly balanced, 0% tongue weight. When you go to pull the model forward it can tend to steer left or right with any little change in side force at 0% tongue weight.

When the TT axle shifts 10 to 15% behind the center of gravity, the tongue is heavier and once you create enough forward force to lift the tongue up off the ground, it wants to track straight ahead and not wander left to right. It takes a lot more force to have it break free from traveling straight then it does at 0% tongue weight.

Try it. Ill see if I can find this better explained. Every site I find keeps stating the 10 to 15% center of gravity shift, but does not explain why. The tracking ability to resist fish tailing is the reason, just I have not found anything one on line with a very good explanation of it , yet.

Hope this helps

John

PS here is one site, but I need a better credential one. Says this
http://www.bharatbhasha.com/advice.php/139179
Quote:
Most of us some time in our life have been going down the highway behind a pickup or suv pulling a camp trailer or a cargo trailer, or some other kind of trailer and watched it start swinging side to side slowly, and then a little faster, until you wondered if it was going to pull the tow vehicle right off the road!

There are different reasons that a trailer will fishtail and here are a few:

-#1 The trailer was loaded improperly
-#2 The trailer has axles that are out of alignment
-#3 The trailer has tires that are inflated to different pressures
-#4 The trailer is too large for the tow vehicle pulling it
-#5 The trailer doesn't have good enough brakes

#1 These are some of the most common reasons a trailer will "fishtail" when it has a problem. The most common reason is that it is loaded improperly. When you load a trailer, you should load at least 75% of your load in front of the axles on the trailer. This will put some of the weight of your load on the back of the tow vehicle thus making the trailer follow the tow vehicle. When there is no weight on the tongue of the trailer, it tends to not follow the tow vehicle very well.
And here is from the State of CA. A more creditable source but they do not explain why. See the balance section. http://www.dmv.ca.gov/pubs/dl648/dl648pt12.htm#balance

More later, and yes you are right. On your small TT, one wrong gear move can change the tongue weight % very quickly. Which was why I was recommending the 13% number. That way you stay up off the 10% area.
__________________
Current Sunlines: 2004 T310SR, 2004 T1950, 2004 T2475, 2007 T2499
Prior Sunlines: 2004 T2499 - Fern Blue
2005 Ford F350 Lariat, 6.8L V10 W/ 4.10 rear axle, CC, Short Bed, SRW. Reese HP trunnion bar hitch W/ HP DC

Google Custom Search For Sunline Owners Club
JohnB is offline   Reply With Quote
Old 11-10-2009, 04:56 AM   #11
Senior Member
 
Steve Collins's Avatar
 
Join Date: Apr 2007
Location: New York
Posts: 1,846
SUN #264
Steve Collins is an unknown quantity at this point
One way to think of it is to think of the trailer as a fulcrum viewed from above, in this case it's the axle(s) that are the balance point and the trailer itself is the fulcrum. If there is enough weight behind the balance point, the side to side motion caused by some traffic conditions (wind, passing tractor trailers, sudden stops) can take on a life of its own. Sway is born. It is translated into side-to-side motion of the tow vehicle through a second pivot point; the trailer hitch. There is a double leverage effect at work. The trailer is trying to move the hitch ball left and right and then the forces at the hitch ball are trying to move the left and right.

The tail is trying to wag the dog. The stronger the wag or the heavier the tail, the more the butt of the dog (the rear of the tow vehicle with the pivot point at the trailer hitch) moves from side to side.

If the dog had wheels and was rolling down the road, the side-to-side movement of the butt would begin to affect the dogs direction of travel. Without some compensation for the "wag" effect, Fido's steering becomes erratic and he begins to weave from side to side. Fido can stop wagging the tail which will fix the problem. Even slowing down the rate of his wag fixes the problem. If Fido is heavier, less effect. If Fido is a long dog, less effect.

I don't know the actual physics calculations here but it been proven that trailers with tongue weights in the 12% to 15% range are much less prone to sway problems. There are several definable factors that will affect sway:

The amount of weight to the rear of the axles of the TT.
The overall length of the TT.
The weight of the TT.
The distance from the axles of the TT to the hitch ball.
The distance from the hitch ball to the axles of the TV.
The wheelbase of the TV.
The weight of the TV.
The distribution of the weight in the TV to front and rear axles.

Consider all the 18-wheelers on the road. Many of the trailers have movable rear tandems. Move the tandems closer to the front of the trailer and you get greatly increased maneuvering ability for turns in city streets, backing into places, etc. Move the tandems closer to the rear of the trailer and any potential for sway disappears. You rarely see one on the interstates with the tandems located anywhere but all the way to the rear.

Those with weight-based sway control (Reese DC's) absolutely must have sufficient tongue weight to make the sway control work properly.

The old Ford Broncos and Chevy Blazers (full-size, but extremely short wheelbases) turned out to be terrible TV's with many cases. Short wheelbase was the problem. Move up to a Suburban or pick-up truck (basically the same vehicle but longer) and much of the problem disappeared.

When I moved from a Dodge Quad Cab 1/2 ton, short-bed pickup with a small V8 to the 1 ton Quad Cab, long-bed diesel duallie a lot of things changed. Heavier vehicle, longer wheelbase, and more weight in the front of the truck (diesel engine). All of these things directly affect sway. The difference was night and day.
__________________

'12 F250 4x4 Super Duty PowerStroke 6.7 diesel
2011 to present: '11 Cougar 326MKS
1999 to 2011: '99 Sunline T-2453
SUN264 * Amateur Radio kd2iat monitoring 146.52
Steve Collins is offline   Reply With Quote
Old 11-10-2009, 06:00 AM   #12
Senior Member
 
Join Date: Jun 2007
Location: New Hampshire
Posts: 1,025
SUN #292
Honda03842 is an unknown quantity at this point
Wow! More to think about. It'll give me a lot to think about as I drive towards Washington, NC and across the Bay Bridge.

I had planned to make a wooden mock up of the trailer in order to test the relationship between shape and airflow, in the vain of an early post on improving mileage on this site.

I figure since I'm building it myself and not to concerned about time I can create shapes that might not be cost effective for manufacturers. ALso I have noticed that the addition of a satellite dish to my roof has dropped my average miles/gallon.

I will use the model to try to further understand tongue weight issue.

I do want to assure everyone that I have not really had any problems, tend to be very careful, and rarely touch the trailer's brake controller. I appreciate every single post and really do want to understand why.

In general there is too much 'going along' rather than understanding in our society. Of course not everyone can afford the time or effort to figure out everything, but us old retired guys have time and knowledge is fun and satisfying and thank you all for helping me out.
__________________
Norm and Ginny Milliard
1982 Sunline 15.5 SB
2004 Honda CRV 4 cyl, manual
Honda03842 is offline   Reply With Quote
Old 11-10-2009, 06:10 AM   #13
Senior Member
 
Join Date: Jun 2007
Location: New Hampshire
Posts: 1,025
SUN #292
Honda03842 is an unknown quantity at this point
One other thought, I have never tried to correct sway using steering of the tow vehicle. I see two approaches to correction, accelerating the car or deaccelerating the trailer.

I usually use the latter applying the traielr brakes but expect that speeding up when there's a little sway would also work though generally I would say it's not human nature to want to speed up.

I will say that as we RV, particularly coming down the NJ Turnpike, we were passed by trailers going 15-20 mph faster than us, exceeding the 65 mph limit on their tires. It would seem that an emergency stop at speed the braking differential between the tow vehicle and trailer must become more of a problem.

FInd us in the right hand lane doing 55 and thinking about your thoughtful sway points,
__________________
Norm and Ginny Milliard
1982 Sunline 15.5 SB
2004 Honda CRV 4 cyl, manual
Honda03842 is offline   Reply With Quote
Old 11-10-2009, 01:37 PM   #14
Senior Member
 
Join Date: Jun 2007
Location: New Hampshire
Posts: 1,025
SUN #292
Honda03842 is an unknown quantity at this point
The following statement is from the sierra neveda site in John's email and probably describes why our trailer tows so well and has little sway.

When travel trailers weighed under a ton and were under fifteen feet long, a bumper hitch was all that was really needed because the weight and strength of the tow vehicle just overwhelmed any influence the trailer might have (as long as the trailer weight balance provided good hitch weight). Now, with trailers running over four tons and thirty feet, they are larger and heavier than their tow vehicles and some accommodations may need to be made for safe towing.

The previous paragraph pretty much describes our trailer, about a ton and about 15 feet and I might add with an anti sway bar, goood tires and a good brake controller. As well our trailer weighs a lot less than out tow vehicle.

Back to the reading
__________________

__________________
Norm and Ginny Milliard
1982 Sunline 15.5 SB
2004 Honda CRV 4 cyl, manual
Honda03842 is offline   Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Travel Trailer Tongue Weight Aid - T2499 JohnB Towing and Tow Vehicles 0 05-30-2009 10:41 PM
Changes in tongue weight and load weight......what do I do? Mark Towing and Tow Vehicles 6 08-22-2008 07:27 PM
2008 Eastern M&G Tongue Weight 50/50 Fund Raiser PTHutch Sunline Owners Meet & Greet 1 06-24-2008 02:56 PM
T 2499 tongue weight and hitch strength Hematite Towing and Tow Vehicles 14 08-23-2007 01:48 PM
Trailer Tongue Weight Scale bugbite Towing and Tow Vehicles 8 07-12-2007 09:03 PM



Disclaimer:

This website is not affiliated with or endorsed by Sunline RV or any of its affiliates. This is an independent, unofficial site.


Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -6. The time now is 06:38 AM.