RV Shocks. Who is using them and how do you like them?

[Cate&Rob]

Great graph of under-damped vs critically damped vs over-damped . . . this is what we are discussing! (I think I remember this graph from a first year engineering text book )

This is usually measured in the fore-aft direction (I will get back to this). When I began to consider adding dampers ("shocks" is a really confusing name for these things) I watched the side of the trailer in the mirror. I could not see under-damped motion. The trailer settles after jounce impact very much like critically damped. So, I got Cate to video the trailer in her mirror so that I could study the trailer motion more closely. Essentially "critically damped" with the control element seeming to be the damping in the center spring "equalizer" connection.

In my discussions with Sonny Dismuke (Joyrider designer) he led me to believe that all systems use the same damper regardless of axle diameter. As I have said before . . .this doesn't make sense to me . . . based on several years of automotive damper tuning experience.

Back to fore-aft vs side-to-side . . . Jim Guest brought this into the discussion. I added stronger springs to the left side of my 303RLS to carry the 800 lb heavier weight on that side. (a whole other story). Before this, the trailer would always fall to the left (heavy) side on every road impact. With the springs matched to the load being carried, the trailer now "bobbles" from side to side on road impact. I can see where damping could be an asset in controlling this. (Thanks Jim )

So, I am thinking that the damper sales guys sell their product because the trailer never needed fore-aft damping in the first place. What they damp is side-to-side oscillation which does give the trailer a smoother ride.

I still don't like how the main two brands of dampers require two sets of relatively large diameter mounting holes close together near the centre hanger attachment to the frame. This is a critical load area for the frame rails and most of the frame rail strength is in the lower flange.

In the cost/benefit analysis . . . I'm still not convinced that this would be (a significant amount of) money well spent.

Rob

[Guest]

JeffC,

Great feedback. Take a look at the video I posted on #38 and you will see my Imagine is underdamped at 2 minutes into the video. This input was not severe at all but the underdamped oscillation and the undamped compression (jounce) and rebound can be seen.

Jim

[JeffC]

There is a lot to agree with in the last few posts.

If you can't obtain theoretical perfect, underdamped on the compression stroke is probably better for a trailer but rebound is what makes the ride smooth. The springs themselves do a fine job of compression dampening but the total lack of rebound control is what makes the trailer bounce.

Properly designed suspension systems balance all the componentry to operate in a specific load and speed range. That range is designed to work within the empty and total weight range of the vehicles they support. You should not have to change shocks based on load although the most sophisticated shock and suspension systems do exactly that through a variety of mechanical and electrical means.

However, a perfectly designed shock absorber that will support a 7K axle and a 12-14K trailer is not the same set of specs required for an 8K axle and a 20K + trailer.

OTOH, it is almost certainly better than nothing. I just wish there was a bit more specificity in application.

[Guest]

I ran across this old video I took of the underside of my 2600RB Imagine. Was looking at several different scenarios back then such as simulated sway and aggressive sharp turns on pavement and the effects on the hangers. But for this discussion an interesting observation can me seen at time 2.0 minutes. The drive moves from pavement to dirt and back to pavement where the drive overall was reasonably smooth.

https://www.youtube.com/watch?v=6RhEKItnjCY

Jim

[Guest]

Howard,

Funny I see this example from the internet states " Underdumped" Its supposed to be underdamped but the idea can be seen on the plot.

Thank you,

Jim

[howson]

Guest -- only thing I can do to add to this thread is post your chart for ya! I don't know a thing about what you guys are writing about, other than I know when it works and when it doesn't.

[Guest]

Suspension systems are designed to be critically damped with normal inputs. The graph (if it posts correctly) shows three graphs. Underdamped, critically damped and overdamped. In a passenger car it seems a critically damped system would be ideal where on the heavy truck or heavy trailer I suspect there is a compromise between being critically damped when lightly loaded and slightly underdamped when fully loaded. Taking a shot and thinking this may be a best case compromise. Not trying to talk folks into the shocks but rather I believe, or hope there was some engineering on the best choice of damping for a reasonable compromise.

https://www.bing.com/images/search?v...x=4&ajaxhist=0

[Guest]

All of the above makes sense to me.

A shock absorber has a single function, to dampen oscillation. All shocks are designed to work within specific weight and performance (dampening, rebound, travel, etc) parameters. An empty 450 would still not be optimal using the same shock as a loaded 150. (pick any other analogy that you like, it is the difference in load and travel that I'm talking about)

Using the same shock on a 10K TT and a 20K 5th wheel still does not make sense to me. Is it better than running without? Maybe. Over dampened is not a good thing anymore than under dampened.

I would be much happier if there were two or three different shocks available depending on load.

What about an empty F450 and the same F450 that is fully loaded? Doesn't this imply that the shock is the best all around fit for both load cases? For the TT and 5th wheel, the shock kits are sized by axle diameter. Would having the same shock for a 3 inch 5000lb axle and a 8000 lb axle also be a compromise to cover both load cases? I agree with having a custom tune on the suspension but this is not currently found even on the F450 between being unloaded and fully loaded where the shock handles both cases reasonably well.

[EMetz582]

I made edits to my original post for clarity.

Dexter frames with more standard slides are compatible with Roadmaster and Joyride shock kit...but may require mild mods.

Lipperts kits will NOT work on Grand Design trailers with Dexter frames.

[EMetz582]

My understanding from the posts in this thread was that there was a single shock part number for all the kits. Is that not correct?

You're right. Each kit shares the same shock among brand kit.

You might be over thinking this whole thing. None of the shocks in these kits are Heavy Duty that would have an adverse affect on the trailer.

We're talking about a total weight range delta among kits of 3000-4000. For a generic shock on a trailer, I feel that's a non-issue.

Compression on these shocks is low. Its rebound dampening that really slows the oscillation and results in a smooth riding trailer.

[Guest]

Take a look at other trailers going down the road, watch the axles, not the wheels. Look how much vibration exists. Then look how much bounce is allowed. Shocks dampen all of this, and get the trailer tracking solid as a rock. If you have the time and money, shocks are a significant update for your trailer that will not improve towing from a drivers perspective, but from a trailer and tire life perspective.

I have installed Lippert shock kits on two TT's, one being a 2017 2800bh, with excellent results.

The "older" GD trailers with Lippert frames and Schwintek slides are compatible with the LIppert shock kit.

Dexter frames with more standard slides are 100% compatible with ANY shock kit.

With some mild mods, Roadmaster and JoyRide can be installed, both of which are practically the same design FYI.

I have a Roadmaster 2460 system on hand right now, ready for installation on my 2020 2800bh in Spring. It will not be a quick job like the Lippert kits were.

EMets582,

Great feedback! Thank you,

Jim

[JeffC]

Again, the shocks in each shock kit are selected by the axle size and thus weight range among brands.

If you feel you can better select shock dampening yourself, there are an infinite number of shocks that fit each kit. Esp the Roadmaster and Joyride.

You can also vary the angle to increase and (more so) decrease the amount of dampening. Using your F-450 example, if you felt the provided shocks were too stiff for your trailers weight, simply increase the angle.

My understanding from the posts in this thread was that there was a single shock part number for all the kits. Is that not correct?

[EMetz582]

I would be much happier if there were two or three different shocks available depending on load.

Again, the shocks in each shock kit are selected by the axle size and thus weight range among brands.

If you feel you can better select shock dampening yourself, there are an infinite number of shocks that fit each kit. Esp the Roadmaster and Joyride.

You can also vary the angle to increase and (more so) decrease the amount of dampening. Using your F-450 example, if you felt the provided shocks were too stiff for your trailers weight, simply increase the angle.

[JeffC]

All of the above makes sense to me.

A shock absorber has a single function, to dampen oscillation. All shocks are designed to work within specific weight and performance (dampening, rebound, travel, etc) parameters. An empty 450 would still not be optimal using the same shock as a loaded 150. (pick any other analogy that you like, it is the difference in load and travel that I'm talking about)

Using the same shock on a 10K TT and a 20K 5th wheel still does not make sense to me. Is it better than running without? Maybe. Over dampened is not a good thing anymore than under dampened.

I would be much happier if there were two or three different shocks available depending on load.

[EMetz582]

BTW, shock kits are sizes by AXLE SIZE thus weight range and shock dampening amount well known. (Its not putting F-450 shocks on a F-150 or vise-versa.)

It comes down to the angle of the shock, at actual ride height, where the shock is or is not effective. Too much angle = very little effective dampening.