Posted 2007-04-08 9:46 PM (#58846) Subject: Trailers and weight transfer
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Posts: 2953 Location: North Carolina
An open question to all interested.
We all know that the front wheels of any vehicle do most of the braking. The reason is dynamic weight transfer. Under deceleration, the vehicle weight is transferred to the front wheels. The rear wheels doesn't have the weight and traction to accomplish much braking so are smaller or a lesser design (drums )
The question:
When braking while towing a gooseneck trailer, Does the trailer weight transfer to the rear wheels of the tow vehicle?
Posted 2007-04-08 10:27 PM (#58850 - in reply to #58846) Subject: RE: Trailers and weight transfer
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Posts: 2689
Originally written by hosspuller on 2007-04-08 9:46 PM
An open question to all interested.
We all know that the front wheels of any vehicle do most of the braking. The reason is dynamic weight transfer. Under deceleration, the vehicle weight is transferred to the front wheels. The rear wheels doesn't have the weight and traction to accomplish much braking so are smaller or a lesser design (drums )
The question:
When braking while towing a gooseneck trailer, Does the trailer weight transfer to the rear wheels of the tow vehicle?
Posted 2007-04-09 2:12 PM (#58901 - in reply to #58846) Subject: RE: Trailers and weight transfer
Expert
Posts: 2689
OK, a fuller explanation - more a DIY experiment that you can convince yourself with.
Get a cement block, I think they're about 24x16x12 inches.
Put it on a 2x10 or 2x12 and lift one end until it slides down the ramp.
Try it again in all 6 orientations - having fun ? {take good notes}.
OK, so it slides at pretty much the same angle each time, except the board might be getting sanded so the experiment might not be repeatable with great precision.
Here's the fun part;
Improvise a brake, e.g. nail a small block about 3/4 of the way down.
With any luck the block will stop with no discernible "lift" of the back edge when going lengthwise and laying on it's widest & longest side.
It will probably topple when stood on it's smallest surface with it's shortest side in line with the board.
EDIT;
I meant to include this.
Try nailing on a block that is thicker than 1/2 the cement block's height - and nail a bit of board overhanging so that the cement block will be stopped by a force that is above it's C.of.G.
No WAY will it tip forwards, in fact you will get the "clothes lined" effect.
;END EDIT
Things to think about;
Height of C.of.G
Distance of braking force from C.of.G - measured along the slope.
Height of braking force relative to height of C.of.G.
To reach my conclusion to hosspuller's question I considered (primarily) the height of the trailer's C.of.G relative to the coupler ball.
I think that is a reasonable approach, but I like playing with blocks anyway, so I thought Y'all might want to as well.
BTW, no "weight transfer" takes place, that term is a misnomer.
Now if it was a tanker truck 1/2 full of molasses with no baffles - that is different, VERY DIFFERENT !
(-:
Posted 2007-04-09 8:33 PM (#58940 - in reply to #58846) Subject: RE: Trailers and weight transfer
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Posts: 2953 Location: North Carolina
Okay that question was the bait... here's the rest of the picture. Consider this truck and trailer in an acceleration moment diagram.
Remember ... not at rest, The whole combination is moving. There are multiple force inputs. The truck is braking and nose diving. Does the trailer just ride along? I think not. The trailer brakes are applying an acceleration toward the rear. This makes the whole moment of the trailer rotate around the trailer wheels. The only thing that keeps the trailer from plowing into the road is the truck. Then this generated down force is applied to the hitch ball.
What factors would affect this down force? Anyone care to quantify the generated force?
Posted 2007-04-09 8:48 PM (#58943 - in reply to #58846) Subject: RE: Trailers and weight transfer
Location: Texas
are you looking for the equation? let's see, we have the weight of the trailer, the distance from center of axles to center of coupler....rotational force due to deceleration..... I gotta go rope
Posted 2007-04-09 10:53 PM (#58960 - in reply to #58943) Subject: RE: Trailers and weight transfer
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Posts: 2953 Location: North Carolina
Originally written by Tx. Vaquero on 2007-04-09 7:48 PM
are you looking for the equation? let's see, we have the weight of the trailer, the distance from center of axles to center of coupler....rotational force due to deceleration..... I gotta go rope
Tx V You're right on the money ! No equation just the factors....Now What factors helps stop the rig?
Posted 2007-04-10 12:04 AM (#58963 - in reply to #58846) Subject: RE: Trailers and weight transfer
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Posts: 3
There are two things that need to be taken into consideration when braking a trailer - the forces and the torques. To stop something that is moving you must produce a deceleration or negative acceleration. To do this you must have an overall force toward the rear of the trailer. This force is produced by the road acting on the trailer applied on the tires in the direction opposite to the direction the trailer is moving. But since the trailer has a suspension, this force acting on the tires will actually produce a torque that will cause the trailer to want to rotate nose down. Since horse trailers have two axles there is less rotation than with a single axle but it's still there. The only other thing touching the trailer that can provide a force and torque to compensate for that rotation is the attachment to the truck at the ball. Assuming the truck brakes and the trailer brakes are each acting exactly as they should to stop each respective vehicle at the same rate (which of course they don't) there will still be an additional force in the downward direction on the ball which will in turn push down on the truck at that point to reduce the rotation of the trailer. It can actually rotate a bit by causing the truck to squat a little. So the force pushing down on the truck will be shared between the front and rear axles because of the position of the ball with a GN trailer hitch. So it won't all go to the rear of the truck but some will.
Posted 2007-04-10 5:02 PM (#59003 - in reply to #58846) Subject: RE: Trailers and weight transfer
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Posts: 2
Unless the truck is stopping faster than trailer. Then the shift of weight or momentum to the front axles of the truck will cause the nose of the trailer to stay up or actually raise, putting more weight on the front. If it is pushing hard enough, it could actually lessen the weight on the rear axle which is what will cause a truck/trailer combination to jack knife.
Trailers and weight transfer
