Hitch height

[bobhenry]

I was following a couple good old boys with 5 38" - 42" in in diameter logs about 20' long on a tandem axle trailer. Halfway down a 35 degree grade was a road to the right. The good old boys wanted to turn and did
( more or less) The trailer picked the truck up by the ball and deposited the driver side rear tire dead center in the middle of the hood of a pristene thunderbird with a very hysterical woman screaming at the top of her lungs. Boys that's 3 1/2 ' into the air. They will lift under braking I saw it !!

[Mark Freedom]

I was following a couple good old boys with 5 38" - 42" in in diameter logs about 20' long on a tandem axle trailer. Halfway down a 35 degree grade was a road to the right. The good old boys wanted to turn and did
( more or less) The trailer picked the truck up by the ball and deposited the driver side rear tire dead center in the middle of the hood of a pristene thunderbird with a very hysterical woman screaming at the top of her lungs. Boys that's 3 1/2 ' into the air. They will lift under braking I saw it !!

Yep, trailer brakes are worth their weight in gold when you need them.
Just like a gun, better to have one and not need it, than to need one and not have it.

[brian_bp]

Under braking, especialy trailers with no brakes, all the trailers deacceleration is done by the tow vehicle. As you brake, the trailer is is being pushed into the tow vehicle. If its level, it will push in level. If the trailer is nose high, it will start taking weight off the rear wheels as it raises the coupler assembly. In a panic stop, you can get in the situation where enough weight is lifted off the rear wheels of the tow vehicle and the whole thing jackknifes. Having the trailer level, or slightly downward prevents this...

This doesn't make any sense to me. The effect which is described here is real, but depends only on the ball height - whether the frame of the trailer is level or not is irrelevant.

By this standard, all towing balls should be as low as possible (and there's something to be said for that), regardless of trailer attitude.

Actualy, it depends on the center of gravity of the trailer in relation to the axle (pivot point) and the coupler. Most trailers the CG (up and down, the vertical plane) is above the ball so it indeed usualy pushes down on the bumper of the tow vehicle. But some trailers, usualy utility trailers or boats, with a heavy load close to the pivot point, can get the ball above the CG. I agree, an inch or two probably doesnt matter for 99% of the vehicles and trailer out there. But a lifted 4x4 truck with the ball on the bumper towing a 5x8 utility trailer with a ton and a half of gravel with the nose of the trailer pointed way up is asking for trouble. Remember, we are striving for the safest geometry possable, given the choice of having an ideal situation, or something the "probably is ok", I'll take the former.

Mike

PS: I'm not sure CG is the proper term for what I am trying to say, I mean the center of the mass of the trailer as its mass is deacellerated...I'm sure an engineer can correct my terminology.

Center of Mass is the ideal term, but C of G is effectively the same thing... the meaning is clear.

Yes, the C of M height is relevant too (sorry, I should have acknowledged that), but moving the tongue up and down doesn't change that height in any material way... a trailer tilted nose-up doesn't have a lower C of M than the same trailer tilted nose-down, so the angle of tilt doesn't matter, only the height of the ball. Again, low is good for towballs, at least as far as reducing effect on the tow vehicle is concerned.

If the trailer mass is significant compared to the tow vehicle (such as a ton or more of trailer pulled by a two-ton vehicle), then the trailer should be doing most of its own braking - most of the force should not be through the ball. Braking force applied by the trailer tires will require a corresponding transfer of load from the trailer axle to the tongue (that is, braking the trailer puts more load down on the hitch), so it's hard for me to see a braking control problem related to ball height.

[brian_bp]

I was following a couple good old boys with 5 38" - 42" in in diameter logs about 20' long on a tandem axle trailer. Halfway down a 35 degree grade was a road to the right. The good old boys wanted to turn and did ( more or less) The trailer picked the truck up by the ball...

They will lift under braking I saw it !!

That's several tons of wood, plus the trailer. Let me guess... the "good old boys" didn't have trailer brakes, right?

[caseydog]

Well, we've heard from an engineer, so as an art major, I'll weigh in.

The reason why you don't want the tongue of the trailer tilting too far down, or too far up is because it looks goofy. Looks are the most important thing, after all.

[BPFox]

Does anybody even remember the original question?

For all you engineer want to bees out there, chew on this for a while. My trailer will be level when parked. But when traveling the frame will be raised 8" higher than that level position and I will guarantee I will not have any handling problems associated with this towing position. No sway, no tail wiggle, no nothing. How do I know this? Its easy, this towing position will be factored into the design of the frame. I will need this towing angle to provide the necessary ground clearance. Sorry Mr. Artist, I know it will look funny, but that does not matter much to me. What is important to me is that my floor be no higher than 8" off the ground when level at the campsite. That means the bottom of my frame rails in the front of the trailer will only have 4" of ground clearance. I am shooting for 12" of ground clearance for travel. If you are concerned with an extreme ball to hitch angle, don't worry. The hitch to ball angle will be a perfect 90 degrees. Nothing like a custom frame to handle all of your towing concerns. Peace.

[angib]

I'll be fascinated to see what you're going to build, BPFox - so far, your ideas sound impossible, unless the axle is going to be some feet behind the rest of the trailer.

But I think you're right about the the ability to design a trailer to tow well nose-up - get the weight distribution right in the travel position and I bet there won't be a problem.

Andrew

[BPFox]

Basically I am going to drop the frame in front of the axle. The front portion of my trailer is going to be the "stand up" part. I want to be able to step into the trailer from the ground so the front end will be lowered to accomplish this. One advantage is it lower's the center of gravity. That's a good thing. The problem created is a frame that is only 4 inches from the ground when level. When I raise the frame for towing it won't be any higher than it would have been if I had built the frame straight. To get everything to line up right the tongue is going to be installed on a slight angle. It is kind of going to look a little bit like the nose cone on the Concorde. Not quite as pronounced but it will have a slight dip to it. By doing this I can maintain a low center of gravity. And yes, the trailer will be fairly long. I'm thinking the distance from axle to ball will be somewhere between 11 and 12 feet. I'm thinking it is going to take on some of the same characteristics as a boat trailer. Long wheelbase with most of the weight near the axle. It's one of the reasons boats pull so easy. Longer is better. I'm talking 15' overall length with 12' of that being the body of the trailer. Trailers tend to be top heavy because they are built on frames that are above the axle. A good portion of my trailer frame will be lower than the axle. Hard to tip over a "low rider". Maybe I should consider some hydraulic cylinders to lower my frame right to ground. That way I wouldn't need any leveling jacks....

[G-force]

Your right, the actual angle of the trailer is not an important factor, all that is important is how high above the axle centerline (the pivot point) the center of mass is in relationship to the ball. The frame inbetween can be any shape, bend, angle, etc. Since most trailer frames are built flat, and designed to be towed level, I was genericly using the term "angled up" and "angled down" to indicate an attitude taller or shorter than designed. Lets say you could pick a trailer up and stand it on a balance beam on it front face, and discover where the center of the mass was. Lets say it is 20 inches above the axle centerline. Under braking, assuming the trailer has no brakes, if the ball is right at 20 inches above the trailers axle, all the forward push into the trailer will be in a straight, level vector. If the ball is above that 20 inch point, it will lift the ball as it tries to overrun the tow vehicle. Anytime the ball is below that 20 inch level, the momentum will push the ball downward. Agree? As for trailer brakes, most utility and small tear trailers dont have them. Here in California, you dont need brakes untill you are over 3500 lbs. I agree the forces on a trailer and tow vehicle are very different when dealing with a trailer with brakes.

Under braking, especialy trailers with no brakes, all the trailers deacceleration is done by the tow vehicle. As you brake, the trailer is is being pushed into the tow vehicle. If its level, it will push in level. If the trailer is nose high, it will start taking weight off the rear wheels as it raises the coupler assembly. In a panic stop, you can get in the situation where enough weight is lifted off the rear wheels of the tow vehicle and the whole thing jackknifes. Having the trailer level, or slightly downward prevents this...

This doesn't make any sense to me. The effect which is described here is real, but depends only on the ball height - whether the frame of the trailer is level or not is irrelevant.

By this standard, all towing balls should be as low as possible (and there's something to be said for that), regardless of trailer attitude.

Actualy, it depends on the center of gravity of the trailer in relation to the axle (pivot point) and the coupler. Most trailers the CG (up and down, the vertical plane) is above the ball so it indeed usualy pushes down on the bumper of the tow vehicle. But some trailers, usualy utility trailers or boats, with a heavy load close to the pivot point, can get the ball above the CG. I agree, an inch or two probably doesnt matter for 99% of the vehicles and trailer out there. But a lifted 4x4 truck with the ball on the bumper towing a 5x8 utility trailer with a ton and a half of gravel with the nose of the trailer pointed way up is asking for trouble. Remember, we are striving for the safest geometry possable, given the choice of having an ideal situation, or something the "probably is ok", I'll take the former.

Mike

PS: I'm not sure CG is the proper term for what I am trying to say, I mean the center of the mass of the trailer as its mass is deacellerated...I'm sure an engineer can correct my terminology.

Center of Mass is the ideal term, but C of G is effectively the same thing... the meaning is clear.

Yes, the C of M height is relevant too (sorry, I should have acknowledged that), but moving the tongue up and down doesn't change that height in any material way... a trailer tilted nose-up doesn't have a lower C of M than the same trailer tilted nose-down, so the angle of tilt doesn't matter, only the height of the ball. Again, low is good for towballs, at least as far as reducing effect on the tow vehicle is concerned.

If the trailer mass is significant compared to the tow vehicle (such as a ton or more of trailer pulled by a two-ton vehicle), then the trailer should be doing most of its own braking - most of the force should not be through the ball. Braking force applied by the trailer tires will require a corresponding transfer of load from the trailer axle to the tongue (that is, braking the trailer puts more load down on the hitch), so it's hard for me to see a braking control problem related to ball height.

[brian_bp]

Your right, the actual angle of the trailer is not an important factor, all that is important is how high above the axle centerline (the pivot point) the center of mass is in relationship to the ball. The frame inbetween can be any shape, bend, angle, etc. Since most trailer frames are built flat, and designed to be towed level, I was genericly using the term "angled up" and "angled down" to indicate an attitude taller or shorter than designed. Lets say you could pick a trailer up and stand it on a balance beam on it front face, and discover where the center of the mass was. Lets say it is 20 inches above the axle centerline. Under braking, assuming the trailer has no brakes, if the ball is right at 20 inches above the trailers axle, all the forward push into the trailer will be in a straight, level vector. If the ball is above that 20 inch point, it will lift the ball as it tries to overrun the tow vehicle. Anytime the ball is below that 20 inch level, the momentum will push the ball downward. Agree?

Yes, now we're on the same page.

As for trailer brakes, most utility and small tear trailers dont have them. Here in California, you dont need brakes untill you are over 3500 lbs. I agree the forces on a trailer and tow vehicle are very different when dealing with a trailer with brakes.

"Need" on a legal basis and "need" on a technical basis are very different things. If I put a 3499 lb trailer behind my Focus and drive it through California without brakes it might be legal (although probably not) but it's still a really bad idea... that's why my comment about the trailer mass being significant compared to the tow vehicle. It seems strange to worry about the detail of matching the ball height to the centre of mass height of the trailer while ignoring adequate braking.

[brian_bp]

BPFox, your tilting trailer design is very much like some industrial equipment trailers which I've seen on the road here in Alberta. They are pulled as semi-trailers (fifth-wheel at the front, axle at the very back), and are basically a rectangular box which looks like it sits directly on the ground at the job site, and is tilted nose-up significantly to tow. Yes, the fifth-wheel plate is level when towing, and at a significant angle to the box of the body. I suspect that they use air suspension on the trailer axle, but that's only a guess.

Sorry, no photo available.

[BPFox]

BPFox, your tilting trailer design is very much like some industrial equipment trailers which I've seen on the road here in Alberta. They are pulled as semi-trailers (fifth-wheel at the front, axle at the very back), and are basically a rectangular box which looks like it sits directly on the ground at the job site, and is tilted nose-up significantly to tow. Yes, the fifth-wheel plate is level when towing, and at a significant angle to the box of the body. I suspect that they use air suspension on the trailer axle, but that's only a guess.

Sorry, no photo available.

Bingo! I have long felt there is too much wasted space under the trailers. I am trying to make better use of that space. Some of the larger travel trailers look so high you could drive a Corvette under them without hitting anything. Then you need a small set of porch steps just to get into them. It's going to look a little goofy going down the road, but I hope it will be sweet set up when parked, which is when I plan to enjoy it most.

[Jason and Amanda]

I'm surprised that nobody has asked the OP (original poster) what his tow vehicle is and how much his trailer weighs.... this no doubt has the greatest impact on towing regardless of the other factors.

You can't pull a 7500lb boat with a front wheel drive sedan. (stating the obvious just to open my next statement) Pulling a teardrop with a small car is not something to be taken lightly... from an insurance perspective think about this. Lets say you have a honda element (which I did a while back and remember the numbers) and you want to pull an 1100 lb teardrop, which is slightly heavier than probably what an average one is but lets just use that number for sake of clarity. So you have a vehicle with a 1500lb towing capacity that (if you use the honda hitch) has a class I hitch installed with a max capacity of 2000 lbs (that's the lowest class). Now the GVWR of a honda element is 4450 lbs. the element itself weighs in at 3500.

So READ CAREFULLY... even though the towing capacity of the element is 1500 lbs, you can only carry, about 1000lbs of stuff, add 2 people, a 150 lb tongue weight (trailer doesn't take away from GVWR, you have to look at the GCWR for trailer + tow vehicle numbers) and say 200 lbs in gear and your left with a measly 325 lbs to spare which you still have to subtract from that the weight of your cars fuel.

Now in this example you will still be below your max for insurance reasons but again you should really never exceed 80% of your vehicles max ratings in any category for safety reasons.


Ok back on topic here, OP what is your tow vehicle and how much does your trailer weigh?

And to answer the popular question, a 1" difference in height won't make any significant difference at all.


*EDIT* Hmm I seem to have forgotten to take my sanity medication this morning, also must have forgotten to take my eyesight medication as well. The OP is pulling with a minivan, so it's still front wheel drive but weights a bit more therefore has a bit better braking and stability. I'm sure the towing capacity is probably 1500 lbs (or thereabouts) so I would guess that anything around level is fine, it will lower once it's loaded with food and camping supplies. unless you fill the galley with more weight than the storage area

[brian_bp]

I'm surprised that nobody has asked the OP (original poster) what his tow vehicle is and how much his trailer weighs.... this no doubt has the greatest impact on towing regardless of the other factors.

Sure, and those were good points, but he wasn't asking about weight or towing capacity - the subject was coupling height and trailer level.

The OP is pulling with a minivan, so it's still front wheel drive but weights a bit more therefore has a bit better braking and stability. I'm sure the towing capacity is probably 1500 lbs (or thereabouts)...

A properly equipped V6 Dodge Grand Caravan - like most recent minivans - will have a towing capacity of at least 3000 lb.

[frank_a]

I expect to build my TD chassis from angle with leaf springs on their own angle spring holder that can be bolted to the chassis at whatever distance back gives me the correct tongue weight. I do not like the idea of having a fixed axle trailer.

My '72 Sylvan 6 X 8 tilt utility trailer has a fixed axle in the exact center of the trailer and I've considered eliminating the tilt and building spring hangers and moving the axle back. When I have to travel empty on highways, I can't really go over 55 without sway. Once it's loaded no problem.

As to ball height, all my trailers are at +/- 1" and I have two different receivers to use depending on tow vehicle and trailer.

Frank