Trailer - should it be horizontal or not.
Submitted: Wednesday, May 05, 2010 at 19:06
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Spade Newsom
I have been reading through a few threads about axles and
suspension etc. and there seems to be much consensus and no discussion to the contrary that the trailer when towed should be horizontal.
I have always understood that the trailer should have a very slight angle tilting toward the tow vehicle. The reason being that under heavy breaking the trailer should place some downward pressure on the rear wheels of the tow vehicle but not sufficient to lever upward pressure on the front wheels. Upward pressure from the trailer on the rear wheels of the tow vehicle was the most dangerous scenario in a heavy breaking situation.
The difference in weight between the trailer and the tow vehicle, the breaking capability of the trailer as
well as the
suspension of both obviously has a major bearing on performance under braking.
I am interested in comments from those that have an opinion on this. Maybe from an angle of fuel consumption, general driving performance or even actual experiences under heavy breaking.
Reply By: Sand Man (SA) - Wednesday, May 05, 2010 at 19:24
Wednesday, May 05, 2010 at 19:24
Spade,
I would think the angle would not be all that important, apart from asthetics.
The more important issue is that the tow ball weight is within correct specifications of the vehicle's capability.
I have actually seen a late model Landcruiser towing a sizeable caravan on a bitumen road in the metropolitan area bucking like a half broken-in horse at a Rodeo.
Very scary it was just to look at. God knows what the goose behind the wheel thought of his rig.
Bill.
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Follow Up By: Spade Newsom - Wednesday, May 05, 2010 at 19:48
Wednesday, May 05, 2010 at 19:48
Sand Man, he may very
well have been within his ratings limits but you suggest this was a dangerous set up. Legal doesn't always translate to safe (and vica versa).
The guts of my post was really about the behaviour of the rig under brakes.
I actually remember reading a transport department guide to towing in the mid eighties about hitch angle and I guess it is something that just stuck with me. Maybe I just remembered it incorrectly.
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Reply By: Rockape - Wednesday, May 05, 2010 at 19:36
Wednesday, May 05, 2010 at 19:36
If the trailer weighs say 1000kg, then the rule of thumb is 10percent of that weight should be on the ball. 100kg.
So you just have to load the trailer correctly.
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Follow Up By: Spade Newsom - Wednesday, May 05, 2010 at 19:52
Wednesday, May 05, 2010 at 19:52
Rockape
Hitch angle, I would have thought, has as much to do with the basic differences in the make of the towing equipment of the trailer and the tow ball height of the tow vehicle as it has to do with the weight on the tow ball.
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Follow Up By: Rockape - Wednesday, May 05, 2010 at 20:13
Wednesday, May 05, 2010 at 20:13
Mate,
your trailer shoud sit on the ball and be level, in a perfect world. You can get adjustable hitches that vmove up and down to the required height or tongues that are bent down or up to the right height so all is level.
Mine is adjustable and from memory I have it dropped down about 225mm to obtain level.
Incorrect loading of the trailer is the biggest worry, if you stick to the 10 percent on the ball all will be
well.
Hayman Reece have a good explanation and advise on all aspects of towing.
Link
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Reply By: Member - Duncs - Wednesday, May 05, 2010 at 19:38
Wednesday, May 05, 2010 at 19:38
I tend to agree with Sand Man,
My first experience at towing a heavyish trailer did not go
well.
I had a V8 Torana and was confident that it could tow anything. So I borrowed a mates 7x4 and filled it with quite heavy gear. It did sit slightly high at the rear but because I had been concerned about putting too much weight on the back of the car I had loaded it tail heavy.
On a long downhill near
Nambucca Heads the trailer started to pull the car around. I could not slow down because that made the sway worse, I could not speed up because the guy in front was slowing down and I had nowhere to go. Thankfully it ended without causing damage to anything or anyone.
I eventually pulled up and relocated some of the gear to the front of the trailer. What a difference. It was still tail high but the balance was so much better. In all the time I have been driving that was probably the most dramatic and effective lesson I have ever been taught.
So in short, get the weight right and don't worry too much about the look. That in mind my trailer tows pretty flat.
Duncs
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Reply By: Member - Mark G Gulmarrad - Wednesday, May 05, 2010 at 20:32
Wednesday, May 05, 2010 at 20:32
gday all
wouldnt the theory be that the hitch should be slightly lower than the trailer on the tow tongue to give the tow hitch down force so as (in a tow ball set up ) the tow ball isnt relying on the catch under the tow ball hitch to keep the trailer attached to the tow tongue?
my 2 cents,cheers.
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Reply By: Allan B, Sunshine Coast, - Wednesday, May 05, 2010 at 20:32
Wednesday, May 05, 2010 at 20:32
Under braking, the momentum of any load above the height of the trailer axle (which in fact is the whole trailer tray and its load) will try to continue forward and in so doing will rotate around the axle. This will in turn produce a downward thrust on the tow-ball and thus the rear wheels of the towing vehicle.
Under heavy acceleration the reverse will apply.
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Reply By: Fatso - Wednesday, May 05, 2010 at 20:46
Wednesday, May 05, 2010 at 20:46
Interesting subject you chose here Spade.
I would guess that, given a perfect scenario, when the trailer brakes were applied the trailer its self would pitch forward & exert an increased downward pressure on the tow vehicle. In that case I would think that being level or not could have a minimal effect.
With an unbraked trailer the transfer of upward or downward force would have to be in relation to where the most kinetic energy is stored in the load in relation to the tow ball & axle.
A load with a majority of mass up high will have a greater downward pressure than one with the mass down low.
I would think that if the mass were under the tow ball height it would give a lifting effect on the tow ball. That would be increased even more if the mass was under the axle as
well (pendulum effect).
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Follow Up By: Allan B, Sunshine Coast, - Wednesday, May 05, 2010 at 21:41
Wednesday, May 05, 2010 at 21:41
Fatso, it matters little whether the decelerating force is applied by the trailer brakes or the tow-vehicle brakes. If the tow-vehicle brakes are applied, the decelerated load being restrained at the tow-ball, will convert to a vectorial force rotating around the axle and tyre/road contact to act down on the tow-ball.
And yes, loads below the tow-ball will produce a lifting action.......but how many loaded trailers have much mass below the tow-ball other than the
suspension and wheels?
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Reply By: Peter_n_Margaret - Wednesday, May 05, 2010 at 21:47
Wednesday, May 05, 2010 at 21:47
I reckon............The change of load on the ball is all about the height of the trailer CofG Vs the height of the axle Vs the length from the axle to the ball and the rate of deceleration acting on the CofG.
Angle of the draw bar won't matter. Height of the hitch might have a minor effect on the tug's response, but the distance of the hitch behind the rear axle is critical.
Cheers,
Peter
OKA196 Motorhome
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Follow Up By: Peter_n_Margaret - Wednesday, May 05, 2010 at 22:37
Wednesday, May 05, 2010 at 22:37
In other words........
The less the weight of the loaded trailer is, the better.
The lower (to the ground) the weight of the loaded trailer is, the better.
The longer draw bar is, the better.
The shorter the hitch overhang behind the tug axle is, the better.
Cheers,
Peter
OKA196 Motorhome
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Reply By: Member - Mark G Gulmarrad - Wednesday, May 05, 2010 at 22:11
Wednesday, May 05, 2010 at 22:11
gday guys
just googling a few sites and came up with this one
Towing guide ....seems to explain things in plain english,cheers.
AnswerID:
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Reply By: Maîneÿ . . .- Wednesday, May 05, 2010 at 23:46
Wednesday, May 05, 2010 at 23:46
On a similar thought, when I tow the boat it cuts the corners, hitting most roundabouts, unless I go right out, however the camper trailer would follow exactly the vehicle wheel tracks.
Question is how do you get the boat trailer wheels to follow the vehicle wheels ??
Do you move the axle forward ??
(I can a bit if need be)
The distance between the trailer wheels and rear vehicle wheels is a lot longer than back vehicle wheels to front wheels.
Maîneÿ . . .
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Follow Up By: Dave(NSW) - Thursday, May 06, 2010 at 08:20
Thursday, May 06, 2010 at 08:20
Mainey,
Just remember that if you move the axle forward on the boat trailer you are also moving the weight back, Also the longer the wheel base from tow hitch the easier it is to reverse.
Cheers Dave...
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Follow Up By: Nargun51 - Thursday, May 06, 2010 at 10:17
Thursday, May 06, 2010 at 10:17
Short answer; the closer the trailer axle is to the front wheels of the tow vehicle the more closely it will track.
If you pull out a high school maths book you can work it out; simple geometry.
First, if you know the turning circle of the vehicle’s inside front wheel and the wheel base of the vehicle you can work out the turning circle of the vehicle's inside rear wheels a further 2 calculations based on the distance from the rear wheel to the tow bar and the width of the vehicle you can work out the turning circle of the tow hitch. The same calculation based on the distance from the hitch to the axle will give you the turning circle of middle of the axle and the same calculation, based on the width of the axle will give you the turning circle of the inside wheel of the trailer.
A narrow short wheel base vehicle with minimum overhang towing a narrow small trailer with a short draw bar will track closer to the tracks left by the front wheels
Uncomfortable to ride in when towing and a sod to back
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Reply By: Dion - Thursday, May 06, 2010 at 07:34
Thursday, May 06, 2010 at 07:34
Horizontal is generally accepted, the wheels being in contact with terra firma is better.
Cheers,
Dion.
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Reply By: Spade Newsom - Thursday, May 06, 2010 at 10:51
Thursday, May 06, 2010 at 10:51
There seems to be some difference of opinion as to what force will be applied to the tow hitch under heavy breaking. There are too many variable situations for there to be an exact answer.
There is a suggestion that regardless of the hitch angle there will be downward pressure. What affect does different hitch angles have on the amount of pressure and more importantly to me what affect would that have on vehicle control under heavy breaking.
I have always, for anything with decent weight, had either a slight downward angle by design or unavoidably a severe downward angle by bad design, so can anyone suggest the general road handling differences between towing horizontal and having some hitch angle. Hitch angle can be caused by hitch design or by poor
suspension or both.
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Reply By:- Thursday, May 06, 2010 at 18:54
Thursday, May 06, 2010 at 18:54
Interesting question spade - I don't have a clue about the performance when on the road.
I do wish to point out though, that if the trailer is horizontal, or slightly tilting down to the front, its way easier to set it up level for a decent night's sleep (without disconnecting it from the vehicle) - just use the jockey wheel to get it level. If it were tilting up to the front - might be a bit grouchy in the morning...
Cheers!
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