Rear Springs Question (1 Viewer)

[LanceL]

So I recently put King's 2.5's on my 200 with Dobinson's 559V rear springs (recommended by Flithy Motorsports) and I'm under the impression that these rear springs may be too stiff. I was a little surprised at how high it sat with them on (and I noticed another poster on here had the same reaction with these springs) and it hasn't settled (still sits over 2" higher than stock in the back after about 4 months). The height part doesn't bother me too much, as I had the front preload adjusted to match the rake I wanted, but I'm not happy with the ride. The front doesn't seem to be the issue, but the back of the truck feels....off. With the compression adjusters at 0, it feels bouncy and wobbly (lots of abrupt side to side swaying) over dips, and if I crank them up, the wobbliness subsides, but the ride becomes to harsh and jarring over potholes. The truck is otherwise very stock, 3rd row removed, no steel bumper or armor or long range tank.

As a test, I put about 300lbs of stuff in the back, turned the adjusters up to 12, and noted the ride was definitely improved. Not too jarring depsite the higher adjuster setting, and far less wayward wobbling.

I measured the thickness of the Dobinsons coils, and the wire is 19.5mm, which is WAY thicker than stock, and I believe also thicker than the OME 2721's, despite being listed as "no additional load" springs. Could the stiffness of the springs be what's causing the ride issue? I rarely load the truck up, so I don't need/want all the extra rear load capacity, and I'd rather not have to carry around 300lbs of lead plates everywhere just to make it ride nicely. Was thinking of going back to stock springs with spacers for a bit of extra height as an alternative?

 

[bloc]

Wire diameter is only half the story as the number of wraps is equally as important. If you hypothetically doubled the number of wraps of a given wire the spring rate would be half.. or close to it anyway.

The wobble you are describing isn't a spring issue it's a panhard rod geometry issue. The more you raise static ride height, the further away from horizontal the panhard gets, and the more "sagitta" is introduced.. basically the axle is moving side to side with compression since the panhard isn't level, the axle end of it is moving in an arc instead of closer to straight up and down as stock.

This video explains the phenomenon well



You need a panhard relocation bracket to correct the geometry..

Panhard drop bracket option?

Does anyone know if any company makes a panhard drop bracket to bring the rod back into a neutral position for the 200 series?

forum.ih8mud.com

Or springs that bring you back closer to stock ride height.

 

[TeCKis300]

There's more going on and multiple things at play.

As @bloc pointed out, your lift height is aggressive putting you in a range where sagitta is an issue and a panhard relocation bracket is needed to fix the geometry. The reason increasing damping helps is because it's absorbing and reducing suspension deflection when hitting bumps, minimizing wonky sagitta affects. Lifts of less than ~2" will have relatively less issue with lateral motions (but still more than stock).

To your other point, ride quality suffers as increasing compression damping has the overlapping effect of making the suspension feel firmer. Perhaps on top of an already stiff spring. This will take some consideration, but understand that ride quality is primarily driven by spring rate because damping generally has to be adjusted commensurate to spring rate. A stiffer spring will need relatively more compression damping for control, arriving at an overall stiffer feel. Otherwise too little damping results in what you found to be underdamped and bouncy.

You may very well want a spring with less rate, which is somewhat independent of height considerations.

Suspension is always a mixed bag with interactions and trades.

 

[LanceL]

Wire diameter is only half the story as the number of wraps is equally as important. If you hypothetically doubled the number of wraps of a given wire the spring rate would be half.. or close to it anyway.

The wobble you are describing isn't a spring issue it's a panhard rod geometry issue. The more you raise static ride height, the further away from horizontal the panhard gets, and the more "sagitta" is introduced.. basically the axle is moving side to side with compression since the panhard isn't level, the axle end of it is moving in an arc instead of closer to straight up and down as stock.

This video explains the phenomenon well



You need a panhard relocation bracket to correct the geometry..

Panhard drop bracket option?

Does anyone know if any company makes a panhard drop bracket to bring the rod back into a neutral position for the 200 series?

forum.ih8mud.com

Or springs that bring you back closer to stock ride height.

So this was my original thought as I was familiar with the panhard geometry problems lifts can cause, so I got an Eimkeith panhard relocation bracket and welded it in, definitely helped with the “butt wiggle” issue, but not the “wobble” issue. Suspension problems are very hard to describe, but the wobble is much lower frequency response than the sagitta induced wiggle. As best as I can describe, the feeling is that when a dip or depression in the road is hit by just one side of the truck, the front drops in, the truck leans slightly, and bounces back smoothly, whereas the back seems to exaggerate the response, plunging into the dip and then violently heaving back up, before settling out. (Exaggerated semantics to convey my point, it’s not dangerous, just bothersome) It only has one cycle, so it doesn’t act like a typical underdamped response, it just has a much more significant response than the front for the same initial displacement condition. Increasing the compression adjusters mostly mitigates this behavior, but the high frequency response (potholes and the like) becomes unbearable, like a buckboard cart. I was thinking perhaps the increased lift is outside the realm of what the sway bars can handle, but it still corners well with minimal body roll, even under vigorous steering, so the kdss appears to be doing its job. It’s the ‘one wheel affected at a time’ scenario where the behavior is particularly poor……

 

[TeCKis300]

So this was my original thought as I was familiar with the panhard geometry problems lifts can cause, so I got an Eimkeith panhard relocation bracket and welded it in, definitely helped with the “butt wiggle” issue, but not the “wobble” issue. Suspension problems are very hard to describe, but the wobble is much lower frequency response than the sagitta induced wiggle. As best as I can describe, the feeling is that when a dip or depression in the road is hit by just one side of the truck, the front drops in, the truck leans slightly, and bounces back smoothly, whereas the back seems to exaggerate the response, plunging into the dip and then violently heaving back up, before settling out. (Exaggerated semantics to convey my point, it’s not dangerous, just bothersome) It only has one cycle, so it doesn’t act like a typical underdamped response, it just has a much more significant response than the front for the same initial displacement condition. Increasing the compression adjusters mostly mitigates this behavior, but the high frequency response (potholes and the like) becomes unbearable, like a buckboard cart. I was thinking perhaps the increased lift is outside the realm of what the sway bars can handle, but it still corners well with minimal body roll, even under vigorous steering, so the kdss appears to be doing its job. It’s the ‘one wheel affected at a time’ scenario where the behavior is particularly poor……

Rear spring rate is too high.

A way to think about this is that springs store and reflect energy. Shocks absorb and dissipate energy.

Turning up the dampers helps absorb energy on compression and rebound. Without sufficient damping, the spring will kick back with as much energy as was put into it going into the dip. With high spring rates, it can be a tough balance to have enough damping for these conditions while minimizing the firmer feel of small high frequency bumps for ride compliance and comfort.

KDSS works as a stiff sway bar on-road furthering the need for sufficient damping.

 

[bloc]

Also, it’s just taller, with a higher CoG. There will be more momentum any time the body does roll in one direction…

Different rear coils are relatively cheap and easy to try, so I think you are on the right track. I do think stock plus spacer will be too soft.. though you already have them. Could easily throw them in as a very low-rate contrast to see what that does with the bad behavior.

Good that you already have panhard sorted out though.

 

[LanceL]

Also, it’s just taller, with a higher CoG. There will be more momentum any time the body does roll in one direction…

Different rear coils are relatively cheap and easy to try, so I think you are on the right track. I do think stock plus spacer will be too soft.. though you already have them. Could easily throw them in as a very low-rate contrast to see what that does with the bad behavior.

Good that you already have panhard sorted out though.

Unfortunately I was a shortsighted fool and tossed my original stock springs with a causal “won’t be needing these old things again!” when I upgraded, which of course I now regret! So I’m debating flushing a few hundred dollars just to get another set for testing purposes, or if I explore other options.

 

[bloc]

Unfortunately I was a shortsighted fool and tossed my original stock springs with a causal “won’t be needing these old things again!” when I upgraded, which of course I now regret! So I’m debating flushing a few hundred dollars just to get another set for testing purposes, or if I explore other options.

Someone near you probably has a set lying around.