Trailer axle/tire question

[Skyco]

We're talking about tandem axles not duals.
The equalizers on tandem leaf spring axles insures the weight will be the same on both axles regardless of trailer loading. That is why they are called equalizers
Also you failed to consider the rotational torque under braking forcing more weight to the rear axle thereby making it the one with greater traction.
The equalizer is what causes this action. Independently sprung systems (no equalizer) operate completely differently.

 

[pat32rf]

Up here any trailer over 2000lb must have brakes, and if its a tandem it shall have brakes on BOTH axles, not just the one with the flat tire!! ;-)

 

[LBrown59]

1*To mandate that all trailers have dual axle brakes is trying to require things that aren't always necessary, just because in your case they are.
2*If dual axle brakes were always needed, there would be no single axle trailers on the road.
David from jax

1*I'm not advocating that all trailers have 4 brakes ; but that all trailers have brakes on all wheels.
2*that's fine if the trailer has just 2 wheels.

 

[Wis Bang]

The first question is 'Does the suspension use the equlizer system or are the two axles sprung independently?' I would suspect that an independent system might shift the weight to the froward axle while the equalizer would do the opposite. Independently sprung axles would also cause different frame stress points and would require different re-inforcement in the design process as well as different behavior when crossing dips and other un-even pavement situations.

I'd start visiting places w/ trailers on display and start looking how the manufacturers do it. You can pace along side a trailer and get a feel for how the axles are spaced, etc.

Also make sure you understand why they gusseted some areas and not others & make sure you have good penetration on your welds.

 

[David Devuono]

I have built a few trailers, Only one twin axle which I put two braked axles on. I have checked out a lot of custom trailers from the Jeep-trailer queen types. I think a lot of the front axle\rear axle brake discussion should keep in mind the method of springing the axles. Weight bias moves forward during braking so if you were using axles bolted solidly to the frame or Torsion axles, you would likely put the brakes on the front axle. If you are using conventional spring axle with an equalizer, as the front axle dives, it forces the rear axle down. This lifts the front axle and you loose a lot of the braking effort. If you add the brake to the rear axle, you will have more braking effort as it will carry more of the load as its forced down? Makes sense to me now that I think of it.

 

[David Devuono]

Wis Bang, you type faster then I.

 

[David Devuono]

So as I am getting ready for my first trailer pull this spring I was going to check the brake adjustment as it seems one axle locks up before the other. Now I understand I would be wasting my time and will investigate the resistor idea, or live with constantly adjusting the trailer from the brake controller?

 

[Wis Bang]

We're talking about tandem axles not duals.
The equalizers on tandem leaf spring axles insures the weight will be the same on both axles regardless of trailer loading. That is why they are called equalizers
Also you failed to consider the rotational torque under braking forcing more weight to the rear axle thereby making it the one with greater traction.
The equalizer is what causes this action. Independently sprung systems (no equalizer) operate completely differently.

Close, the equalizer lets the axles move with the teraine conditions while allowing the weight of the load to be equalized between the axles. Examine the setup on a tractor trailer, the spring ends hook into the equalizer and the outboard ends float in the spring hangers and the 'torque arms' keep the axles in position. Utility trailer axles use shackles instead of floating the spring ends. Equalizing the weight on both axles prevents overloading the frame.

 

[Skyco]

Ok for all you doubters I emailed the two leading axle manufacturers, Dexter and Alko, with the question of which axle on an equalized leaf spring system gets the brakes.
Not surprisingly both recommended both axles but said if only one axle gets brakes it should be the rear.
BTW they both answered on the first business day, I'm impressed.

 

[sandman2234]

Dexter makes good stuff, and stands behind it, last I purchased. Haven't done any with the other manufacturer you mentioned.
I still disagree with lbrown, in saying all axles should have brakes. Depends on what you do with it. If a single axle trailer will work, and you opt for a dual axle just because you hate to overload the p.o.s. tires they put on them nowadays, then single axle brakes should be fine. Pulling lawnmowers is an example, on a 6x12 foot single axle trailer. Add a second axle just to make it pull better going down the road, and why should you have to add brakes? If you say something, then you have to figure all of the angles, or your just spitting out bull.
David from jax

 

[Skyco]

You are entitled to disagree all you want.


I would never own a tandem with just one axle brakes, but I wear a seatbelt, don't drink and drive and look both ways before crossing the street <shrug>

 

[4shorts]

I would not put brakes on 1 axle.

Why? I do service and repair work for the Department Of Fisheries here in Newfoundland, Canada and most of there tandem trailers only have brakes on the forward Axel and there all factory trailers that carry very large Boston Whaler boats. Just curious your reason for your statement.

 

[Skyco]

Don't the Whaler trailers use torsion axles rather than leaf spring equalized setups?
If so that's why they are on the front axle.

 

[RWolf]

My 2 cents I would "prefer" to have both axles with brakes. Why? More braking force. I don't know about anybody else but I've experienced brake fade on my trailer and it's not fun. Depending on your controller you can have proportional (pulse), a true proporitional (such as what Ford did) or some other kind of controller. As far as adjusting the controller what I do is (when pulling my horse trailer) I will initially warm the brakes up and after while traveling about 20 - 30 mph use the controller bypass to engage only the trailer brakes. I will set it to stop both the trailer and the vehicle in the quickest time without locking up any trailer brakes. That adjustment will generally provide good stopping force and not rely on the vehicle brakes to much (your mileage my vary ).

 

[J_J]

I don't think I agree with some of you on the weight transfer on a dual axle trailer. I believe that the front axle will get the most weight in the transfer when braking. I am thinking the back axle will try and rise putting less pressure on the ground. That equalizer thingy is not there to equalize weight transfer, but to equalize the load across a larger area, and stabilize the load in a normal towing situation, and keeping the trailer from bouncing to much.. So if you are giving all the brakes the same current, then the back brakes will grab first because there is less friction, and they will lock up first.. So if you want equal braking on the rear, then you would pass less current to the back brakes. This is only assuming that you are towing the same load all the time, then you can fine tune the controller and using a resistor for the back set of brakes. If you are towing different loads, it will be hard to fine tune and get proper braking action. How many of you have seen flat spots in your tires, most probably the back tires, because they grabbed first. So if you want brakes on one axle, then I suggest the front axle is the one to add brakes to, because it is getting the most weight transfer. I could be wrong, but I don't think so.

 

[Skyco]

Ok JJ, did you read my post #29? If you did then why don't you contact the two largest axle/trailer running gear manufacturers in the world, Dexter and Alko, and tell them they are wrong
I'd like to see what they say.

 

[J_J]

Ok JJ, did you read my post #29? If you did then why don't you contact the two largest axle/trailer running gear manufacturers in the world, Dexter and Alko, and tell them they are wrong
I'd like to see what they say.

Yes sir. I did read it, but everybody that builds something says that their products are the best and they only used the most correct data in their design, you know that everyone can't be the best. I am just trying to use a little logic here.

Let me ask you a logical question? If you had only so much current to apply to the electric brakes, and the front axle had 1500 lbs on it and the back axle had 1000 lbs on, which axle would stop first. I hope you say the 1000 lb axle. Now if you took some current from the back axle brakes, do you think they might stop at about the same rate with out either set of tires grabbing. I think the front of the trailer tips down in a severe braking situation, and puts less weight on the rear,and more on the front. If you set the tongue weight correctly, about 15%, you already have more weight on the front, so the trailer is out of balance from the git go.

 

[Skyco]

Nope. The weight is roughly equal on both axles regardless of the loading on the trailer. That is why the "equalizer" is there and part of its function. IF there was NO equalizer then YES the load can vary. That is why it is so important to tow a torsion axle trailer level, they don't have equalizers.


Using your logic about the best- find ANY axle manufacturer that recommends other than the back axle in a tandem equalized leaf spring system. I'd love to hear them explain it.

Look at it this way under braking. Trailer is going right to left. When the front axle brakes, which tends to rotate the axle counterclockwise looking at it from the left side of the trailer. What does that do? It lifts the end of the equalizer attached to the rear end of the front spring. And what does that do since the equalizer pivots? It pushes down the rear of the equalizer attached to the front of the rear spring. That in turn increases the load on the rear axle and decreases the load on the front axle. Less load= less braking ability.

Got that? Agree?

Now look at the rear axle, as it brakes it also tends to increase axle rotational force counterclockwise which pushes down the rear of the equalizer, which in turn lifts the front of the equalizer. What does that do? It decreases the downforce of the front tire even more as it is lifting UP on the end of the leaf spring. So now you have even less downforce (weight) on the front tire resulting in even more loss of traction.

It is really all about simple leverage.

 

[4shorts]

Don't the Whaler trailers use torsion axles rather than leaf spring equalized setups?
If so that's why they are on the front axle.

Nope. The Axels on the goverment trailers are all leaf springs. the torsion system isn't used much around these parts.

 

[Bill_C]

I'm mentally going through the free-body diagram of the axles under braking forces, and I see where Dexter and Alko get their answer.

The front axle spring is fixed at the front of the spring. This is the pivot point for the spring; the spring can move up or down as well as laterally at the rear of the spring. When that axle brakes, the friction between the tire and the road exerts a torque on the axle, from both the direct braking torque and the torque that comes from the force of the tire on the road multiplied by the perpendicular distance from that force to the pivot point. Both of these torques make the axle tend to pivot...upwards off the ground.

The reverse is true on the rear axle. The torque acts in the same relative direction as the torque on the front axle, but the spring is fixed on the rear and free to move upwards or down at the forward end of the spring. The axle will be force downward. If the equalizer didn't stop the spring, in fact the axle could even ride under the spring pivot point and flip....

Nevertheless, I will eventually put brakes on both axles of my flatbed trailer.

edit: I see Skyco also explaine dthis at the same time I was typing. Goes to show great minds must think alike