Thanks! Already got a few of those open in tabs actually. Will read up and probably come back with more q's.

Are FJ80 springs knowns to be taller than LR ones? I ask because it seems stock fronts are 160in/lbs which according to my math are perfect for the extra ~340lbs of diesel motor.

 

yeah i dont think mine rides harsh at all and i commute from va to south n.j. and back once every other month plus its my daily, but i am running i would guess 300# + in winch and bumper with skid, carry hi lift jack on second row floor, have a sd roof rack, home made dog/ cargo barrier, and carry some offroad gear in totes in the boot all the time so guess i got some static weight to help the ride?, and i thought it rode great loaded down with all our camping gear in the boot and on the roof cxrawling around rausch last year

you can watch me going over some rocks on u tube, little bit taller might be nice

 

Yes they are taller, which limits their use.

Take your stock front spring and calculate its compressed length assuming 880lb per tire.
(uncompressed length)-(weight)/(rate) = compressed spring length

16.54 - 880 / 133 = 9.92"

Now take a spring you're considering. Let's say an OME 2851 and let's add 100lbs to the front axle (50lb per front spring).

18.8976 - 930 / 220 = 14.67"

14.67" - 9.92" = 4.75"
In this case we'd gain 4.75" lift in the front even with 100lb extra weight on the front axle. This may or may not be desirable. Calculations work the same for the rear where I usually assume 1320lbs stock unladen weight per spring.

Remember to factor in not just the weight of your engine, but any other additions as well like bumpers, winch, sliders, bigger rear tire, ladder, roof rack, extreme obesity, etc and estimate what portion of the weight sits on which axle.

 

Don't forget you can use spring seat spacers, spring isolators, and D2 spring seats to raise or lower the ride height. This allows you to level truck and use a spring that has the desired rate, but is a little too short or tall.

 

Thanks for all that info! Definitely helps demystify the whole spring/length/weight/rate question.

So, hypothetically, if I wanted a 420lb increase (diesel + 100# provisions for armor) on the front axle with factory ride comfort and 2" lift I'd be looking for a spring:

~19" tall with a 165 lb/in rate

Right? Of course I'll ultimately have to take some other factors into account like the weight of all the fluids, extra batteries, etc. as well as a slight bump in rate to help compensate for higher CG. But I really want to keep the ride comfort (and resulting increase in ground contact pressure) as close to stock as possible.

 

That's about right. I calculated 2.48 inches lift, but you could run D2 rear spring seats in the front to lower it to right about 2 inches.

 

Yep I'll play with it some more to get it just right. More interested in about 3" actually, but it seems comfort vs. wheeling (vs. tire size) vs. stability at speed can be a delicate balancing act!

 

Exactly.

The stock suspension geometry performance goes downhill steeply after 2 inches lift so I'd caution you going for 3, unless you planned on being at 2 while laden with gear. Of course 3 and more has been done many times, but results vary and can require costly investments like DC drive shafts, drilled swivel *****, castor corrected radius arms, corrected rear arms, extended shocks, extended bump stops, etc all for diminishing returns. It's possible to run up to 33s on 2" lift and trimming anyways. Big tires decrease acceleration and crawling ability, and increase risk of breaking diffs and axles, so often HD axles, custom gears, and locking/ATB/LSD diffs are used at considerable cost. Hard core offroaders go big, pay for it, and for them it's worth it. Overlanders tend to go more conservative on the tire size and lift since in reality even a stock truck is highly capable.

 

So how can I add another inch without buying another set of springs?

 

Agreed on the deep dark rabbit hole that is suspension mods... as implied by the OP, I'm really going for a "highly capable" overlanding/camp rig than the technical crawling focused mods. Same with the driveline - at most I'll probably invest in some truetracs.

Currently running 235/85's and am not interested in going any taller than that. If anything a little shorter but widen the stance out a tad. 2" might be the ticket then - how much trimming are we talking about?