Why don't trailers have shock absorbers?

This might be a silly question and I am sure the answer is cost. 

As I sit in my house I constantly hear trailers bouncing and crashing down the road I live on.  Laden or unladen the sights and sounds are the same. If i think back far rnough i remember borrowing a truck bed/frame conversion trailer that still had shocks on it and it towed great and didn't bounve all over rough roads. 

It Just seems to me a set of bargain basement shocks or even friction shocks would improve their manners.

Is there something I am missing? 

I built a trailer once with coil springs. The first time I took it down the street I realized the error of my ways and quickly added brackets and shocks. It handled remarkably well afterwards. Leaf springs are somewhat self-damping, but shocks would certainly help.

In reply to Jumper K Balls (Trent) :

A couple of my customers manufacture trailers. I can guarantee cost is one of the primary driving factors.

I also assume that the loading math is a bit simpler to engineer a top with an axle solidly attached (or on leaf springs) rather than figuring out how the trailer would handle under a dynamic load.

The one I looked up quick, uses Dexter Torsion Axles on their larger trailers which helps quiet things down quite a bit without requiring shocks and springs.

Looking around, Timbren also makes torsion suspension system which eliminates the need for an axle all together.

Both options are pretty spendy though compared to a solid axle of the same load rating.

On the far end of things, airbagged trailer manufacturers seem to exist in greater numbers these days. Awesomely.

we played with the idea, cost is a big one, and they dont really need it. Everything from my 40ft car trailer, to my utilty trailer, none of them would really benefit from shocks. 

Leaf springs self-dampen quite a bit due to the sliding friction between each leaf. In fact old-school road/autox racers would take apart leafs and grease them so the damping properties are smoother and more predictable when using a shock absorber.

dampen (v):  to make wet

damp (v):  to reduce energy in an oscillating system

maschinenbau said:

Leaf springs self-dampen quite a bit due to the sliding friction between each leaf. 

That they do but, when the shocks on the back of a leaf sprung pick up wear out we still replace them to avoid shaking our selves and the loads we haul to E36 M3. 

Leaf sprung trailers can definitely benefit from shocks.  A lot just skip them because it adds cost and people are used to trailers not riding well anyway.  Torsion axles typically don't need shocks (but they have the big downfall of being very sensitive to the trailer being level if it's got tandem axles).  

I have shocks on the two trailers I built. Both leaf sprung. Makes a big difference IMO

AngryCorvair said:

dampen (v):  to make wet

damp (v):  to reduce energy in an oscillating system

Actually, 'dampen' is technically correct.  In fact, the first definition offered by m-w.com is:

"to check or diminish the activity or vigor of :  the heat dampened our spirits"

No shocks on any of the three trailers I've owned.  The two on leaf springs were crashy (HF tire trailer, steel/wood open car trailer), the one on torsion axles is not (TPD 24' enclosed triple axle).  Aside from cost, probably another reason for not putting them on is that there isn't much room.

I don't think I have ever had a trailer that bounced, except for the one that had no springs. That one I have seen 3' off the ground. Shocks wouldn't have helped it either. 

Toyman01 said:

I don't think I have ever had a trailer that bounced, except for the one that had no springs. That one I have seen 3' off the ground. Shocks wouldn't have helped it either. 

 

My tire trailer regularly leaves the ground, even when I have close to 1000lb of stuff on it (on a 1080lb rating), which is also the only time I've ever seen the springs actually flex...

I've never given much thought to shocks on a trailer but our low boy semi trailer for hauling heavy equipment has shocks and airbags. I don't remember any other trailer I've worked on having shocks. 

Knurled. said:

Toyman01 said:

I don't think I have ever had a trailer that bounced, except for the one that had no springs. That one I have seen 3' off the ground. Shocks wouldn't have helped it either. 

 

My tire trailer regularly leaves the ground, even when I have close to 1000lb of stuff on it (on a 1080lb rating), which is also the only time I've ever seen the springs actually flex...

 

 

Might want to lower your tire pressure a bit. 

Surprisingly I do not have pictures of it finished.. but here is the trailer I built for my small sailboat. It is basically a central tube with a box to support the suspension. I run an axle-less torsion suspension on it and it is one of the quietest trailers I have ever had the pleasure to tow. I could hear the license plate rattling over everything else. This includes when not carrying the boat. With the 300+ pounds of boat, it didn't bounce at all. I will never build another trailer with a beam axle.

I built a tow dolly, and it has no suspension.  Towing it empty, it will bounce all over the place! It is scary in fact.   I started to air down the tires when it is unloaded, and air them back up after loading a car.  I don't really use it anymore because I found the straps are a big hassle and you can't back up with it,  but it can be useful when something is too big or heavy for my trailer.

Iusedtobefast said:

I've never given much thought to shocks on a trailer but our low boy semi trailer for hauling heavy equipment has shocks and airbags. I don't remember any other trailer I've worked on having shocks. 

Most semi trailers have shocks, bags don’t give you the damping you need so they run bags and shocks together.

No shocks on my trailer and it rides remarkably smooth. I've forgotten a cup of coffee on the shelf up front, driven a couple hours home and the cup hadn't moved. It was cold so it still got thrown out.

In reply to mad_machine :

That's cool! Where did you find the split torsion setup?

In reply to sobe_death :

Northern Tool & Equipment

In reply to AngryCorvair :

If you really wanted to show off you’d say ‘amortize’.  From Latin: to deaden 

I'm sure it's a cost thing mostly.  Shocks are used on cars to control vehicle dynamics and make a more controlled ride.  Trailers are just things along for the ride and don't need to "carve corners" or anything like a vehicle has to.

There is also a huge difference between the empty weight and loaded weight.  In a car tha weighs 3500 lbs, the GVWR might be 4100, but on a 7000-lb GVWR trailer, the empty weight might be 1500.  Hard to choose damping for such a wide range of possible weights.  It will either be way too stiff unloaded or underdamped when it has weight on it.

Trailers are also not designed to be quiet, comfy things like cars are.  They're designed to be strong and useful.  Dad has a 24' flatbed with big steel ramps that slide into pockets under the deck.  They rattle around in there and could wake the dead.  No amount of damping would change that.