Spring selection analyses (1 Viewer)

[kcjaz]

I currently have BP-51 with 2721s on the rear plus 30mm spacers. Since I installed the springs I have added a lot of weight (winch, full BB skids and a Dissent rear bumper with dual swingouts). I'm still happy with the 2721 though I think I'm at the limit weight wise. As I'm adding a 24 gal LRA in a few weeks, its time to also change the rear springs. I do not have drawers but carry a lot of stuff and will likely add drawers in the next year. So which spring to change to? I've gone back on forth on going to 2723 or 2724. I think 2724 is the right answer.

I came up with 2724 are the right spring based on calculating the compressed height at an assumed load. I don't know what my rig really weight but I'm guessing its in the 7200 lb range loaded for LCDC or something. So just dividing by 4 gives 1800 lb/wheel. I just did the simple math with the published spring rates. The 2721s are progressive so all I did was average the the two rates to calculate the deflection. The result was that either spring (with no spacers) will put me within about 1/4" (7 - 8 mm) of where I would be with the 2721. The 2724's will put me ~8mm higher based on all my assumptions. My future drawers will probably be another 200 lbs (0.5" more squat at 400 lb/in). My analysis is here:

I know I may be over analyzing this but that's what I do. Is there a flaw in my approach or math?

I can fix ride height with spacers if I need to. The thing I do not know is how 400lb/in will "feel" in terms of ride comfort vs. 340 lb/in. I think that is personal preference and the only way to tell is to try one. I would say I'm a bit "floaty" now but I haven't cranked up compression setting on the shocks. (I'm going to do that this week and see).

I can also mess with the BP-51 shock settings. Or potentially use spring rubbers. This is the part of my self inflected "do-loop" where I talk myself back to 2723s because I can "adjust" with spacers, shock settings and/or spring rubbers....

Thoughts/advice???

 

[daneo]

I would "undershoot" with the 2723s. I did similar calculations with the Dobinson's line of coils, and in my experience, the springs wound up providing more lift than my calculations, even after settling miles and time. I now have 4 sets of coils with slightly different levels of "too high" in my garage. Much easier to start low and trim up in my experience.

 

[100kiwi]

I have a very similar setup with the 12.5 gal LRA tank, drawers, Kaymar dual swings.
I run 2723s with air bags. Normally I'm at 4 psi in the bags, add RTT, camping gear, fridge, two 85lb shepherds and and I'm running 20psi in the bags.
It give me adjustability and a good ride when "empty"

 

[kcjaz]

I would "undershoot" with the 2723s. I did similar calculations with the Dobinson's line of coils, and in my experience, the springs wound up providing more lift than my calculations, even after settling miles and time. I now have 4 sets of coils with slightly different levels of "too high" in my garage. Much easier to start low and trim up in my experience.

So was it the height you didn’t like or was there a “too stiff” ride component.

 

[daneo]

It was the height. Haven’t found the spring rate to have a huge influence on ride comfort.

 

[kcjaz]

It was the height. Haven’t found the spring rate to have a huge influence on ride comfort.

You gave good advice that I ignored. My calcs said I’d end up 1/4” higher which I thought would be low relative to actual but thought the difference something like 1/2” more (3/4” total). I actually ended up about +2” (with aux tank empty) though I expect some “settling” over time. I’ll fill the aux tank tonight and see what that does. Theoretically it will squats the rear about 1/2”. Edit: 1/2” is wrong. Would calc to 0.18” for 24 gal.

I’m at the limit of my garage:

 

[daneo]

Wow, that is tight! I've definitely traded paint between my garage trim and GFC by coming in too quick and I have about an inch more space than you. You might have to creep in 4lo to get back in the garage! Fingers crossed the fuel helps you fit.

 

[kcjaz]

Wow, that is tight! I've definitely traded paint between my garage trim and GFC by coming in too quick and I have about an inch more space than you. You might have to creep in 4lo to get back in the garage! Fingers crossed the fuel helps you fit.

Fortunately, the 200 normally lives in a 45x52 metal building with 24’x14’ roll up doors. May need to air down when at home now!

 

[kcjaz]

Filled the aux tank and had no real measurable change in ride height. I pumped 21 gal which would weigh 126 lb which should result in 126/2/400=0.16” deflection.

 

[linuxgod]

Go hop on a CAT scale and let us know your rear axle weight.

I ended up with Ironman medium rears as they were half the cost of OME and more readily available. They’re the equivalent height of a 2723 once loaded. I’m very happy with my setup, both empty and towing.

 

[kcjaz]

Go hop on a CAT scale and let us know your rear axle weight.

Yes. That’s on my to do list.

 

[linuxgod]

Yes. That’s on my to do list.

I’m at 3700 on the rear axle when “empty” or 5400 loaded and with a trailer. I can dig up measurements but I’ve got a decent rake when empty. When the trailer is hitched I’m a half inch or so low in the rear. The ride is really nice

I have a chart if the various spring options with spring rates, free heights, coil diameters, purported recommended weight ranges, etc posted around here somewhere as well. The IM springs I think we’re rated at 286#/in but I only drop about 2”-3” when adding 1700# so take that for what you will. They were longer free length than OME. I used a 10mm spacer on the passengers side and I’m within 5mm left-to-right now

I think with the sale they were $165. I only wish they weren’t green but I’m sure they’ll get dirty eventually, otherwise I’ll spray some rattlecan black. FWIW the paint on them isn’t as good as the Tough Dog springs - the paint chipped a bit in shipping whereas the TD ones got scratched but didn’t chip