Questions for Inland Andy (or other interested party) :-)

[Over59]

If pounds comes off the front axel from hooking up the trailer it has to go somewhere. It isn't going to the trailer axel. It has to go to the rear end. So without the WD you are increasing the rear load by more than just the trailer dead weight. But that's not the big problem.

In normal driving you can load up (add wieght to ) the front tires in order to make a turn with reduced plowing straight ahead. Brake first, let the load come forward, turn, weight shifts to rear wheels, accelerate (only have rear wheel drive in our house). If you look on the inside of bad curves where kids like to play you will see the results of doing this out of order. Turn, fishtail, brake crash. Basic high speed driving school stuff. Well with a trailer it doesn't work like that if it isn't setup correctly with WD and brake controller. With no WD the trailer hitch could dive, loading the ball and raising the front. Now you try to turn and you are in big trouble. The next part is real interesting, The weight bounces around loading and unload the axels in response to the drivers effort to do something. He could compromise steering and braking. The former when the front unloads and the latter when the back unloads. I wonder what it's like to only have the front brakes of the TV trying to stop all that mass and turn in the selected direction at the same time. If the tires break away from the road you are in big trouble. Weight finally bounces to the front, brakes are locked, rear TV wheels unloaded and start to skid. First principle of leading axles. The axel that loses it's grib will try to pass the others. That's why trucks jackknife. I want a setup that is optimize for an emergency braking turn. I want the TV to load up on the front axel, I want the trailer brakes to drain off alot of the energy while still (hopefully) in a straight line and not break free. and if they pull back on the truck that's good. More front loading. Guess I'm just picky. I do go a couple hours with the Caravel on the ball but I keep the speed down even on dry roads and it's 3500 pounds on a 2500HD DuraMax. An aggressive touch of the brake and the transmission will nearly stop you in your tracks. 70mph without a good setup is trouble looking for a place to happen.
Just my opinion.

[59toaster]

I will get back to the original points of the post instead off all the tangents. T



You asked about the bars in relation to the Reese dual cam on a truck with heavier suspension.

Basically here is the high points of the link Mark posted that goes into depth on the subject.


YOU MUST GO TO A LIGHTER WEIGHT BAR! The DC depends on a firm amount of tension from the bars. If that tension relaxes the Dual Cam will loose its effectiveness.

1000lb bar on a 1/2 ton might deflect 2.5 inches to get the TV and coach level.

1000lb bars on a 3/4 ton may only deflect 1.25 inches to the the heavier sprung truck and trailer level.

We don't need to get into it any deeper then the deflection of those bars.

Now I will explain on the DC system so that people who are not familiar with the DC will understand the point of the deflection and understand the point of this post is not as much about weight transfer.

Here is the instructions for the Dual cam that you can look at to see the design.
http://www.reeseprod.com/support/sup...fs/26000IN.pdf

The bars on the trailer end ride in a saddle. They do not connect to the chain at all. The end of the bar has a "Cam" bolted to it. Once the system is tensioned up and that the tow vehicle are in line the cam on the end of the bar centers on saddle. The cam ramps off center. Whenever the trailer and TV come out of line the cams fight this change because the cam slide off its center and start forcing the the bars into a higher tension.

So in the instance of sway the DC is always fighting to keep the TV and coach in line.


Here is where the deflection of the bars play in. Think about what happens when you slam on the brakes hard in an emergency. It is a given that the vehicle will "Brake dive" or "Nose dive". The weight transfer of the braking causes the vehicles nose to drop.

Now think about whats happening at the hitch: If the nose goes down the hitch comes up. If you have a lot of distance from the rear axle to the hitch this will be quite a big change.

Remember the amount of deflection to get the TV level between 1/2 ton and 3/4 ton? Well since there is less defection it lakes less change in hight of the hitch in relation to the trailer before the tension on the end of the bars is lost. Without that firm tension the Dual cam system becomes ineffective.

So right when you need the benefits of the DC the most...in an evasive heavy braking situation....the DC stops working because of the lack of deflection.

You need to go to a lighter rating bar with a 3/4 ton truck to make the DC work correctly. Generally a 250lb drop would be about right when going from a 1/2 ton to a 3/4 ton.

[Mike Lewis]

toaster----I follow your thinking to this point. Given that braking creats "nose dive" ,doesn't the trailer breaks do the same? Wouldn't the nose dive of the trailer offset the "raising" of the TV rear?, at least somewhat?----------
Pieman

[nickcrowhurst]

Pieman, that's a very good question. My analysis indicates that the answer depends on the relative weights and heights of the centres of gravity of the TV and trailer above the axles, the relative efficiency of the two braking systems, and the distance from the hitch ball to the trailer axle center, compared to the distance from the TV front axle to the ball. This can be simplified by assuming a case where the braking decelleration applied to both vehicles are equal, so that the TV is neither pushed nor pulled during braking. Let's also assume that there is no nosediving or lifting of the TV, so that the diving force generated by the decelleration of the TV is exactly cancelled out by the lifting force supplied by the trailer bearing down on the hitch during deceleration. In this case, taking moments about the hitch ball for both vehicles, the mass of the TV multiplied by its center of gravity height above the axles, divided by the TV front axle to hitch ball distance is equal to the trailer mass multiplied by its C.O.G height above the axle, divided by the distance from the ball to the center of the trailer axles.
Using the figures for my rig, there will be no nose-diving if 65 times the trailer C.O.G height is equal to 68 times the TV C.O.G height. This in itself is a useless bit of information, but the practical result is:
If your rig nosedives, taking weight out of the TV and putting it in the trailer would stop this, but it would be bad for overall control, as would raising the C.O.G of the trailer. The safe way is to lower the center of gravity of the load in the tow truck. However, this is probably impractical!
Nick.

[Mike Lewis]

Nick--- my responce was in responce to toasters assumption that the spring bars become unloaded when breaking hard. I would agree if the trailer had little or no brakes. If hard breaking causes nose dive in the TV certainly this same thing would happen with the trailer if equiped with adequite brakes. Not being an engineer it just appears to me that due to the location of the trailers axles in relation to the hitch might even cause more dive there than at the front of the truck. If this is true would it not make the Dual Cam system more effective the harder the braking action? Am I looking at this correctly?? -----Pieman

PS-----The Hensley Arrow video they use to promote their product seems to show what I'm talking about. Their film shows the rear of the TV actually compressed under panic braking.

[nickcrowhurst]

Originally Posted by Mike Lewis

Am I looking at this correctly?Pieman

Mike, yes, I believe so.
Nick