I've been running the Teraflex Outback springs with their 9550 shocks on my JKU for over a year now, on big trips it gets loaded up pretty heavy. I wish I would have weighed it before our Baja trip, but I did not. I'm very impressed with the Outback spring on a loaded JKU, they support the weight well and don't sag like a normal lift spring would. These Outback springs are beefy too, much larger coil diameter than other coils. Unloaded, the ride is pretty firm... if you hit a pothole or expansion joint you feel it. Despite that, if you hit a big roller (dip) on the freeway unloaded the Outback springs are still compliant enough to soak that up and react with a firm, controlled reaction. With a loaded up JK (even a couple hundred pounds) the ride is much better.
If you've seen my Baja trip report or my build thread, you've probably seen this pic.-
I was loaded very heavy, too much weight IMO (the Jeep was a bit top-heavy)...but the springs supported it all well. Starting out we had 10 gallons of gas on the roof, 12 gallons of water, a small propane tank, CO2 tank, camping stove & related gear all on the roof. Inside we had tools, camping gear (tent, sleeping bags, clothing, etc) freezer/fridge, food, bottled water, etc. Plus a 2 gallon Rotopax on the tailgate, spare, Trasharoo. That is also on top of the aftermarket bumpers, sliders, winch, roof rack, etc. (This reminds me, I need to cut down on our packed weight!)
Offroad with lots of weight the suspension is plush at speed, one of the days in Baja we were driving for about 3 hrs in sand and running as high as 55-65 MPH... the Jeep with a heavy load was composed, yet compliant. I was actually impressed how well it handled fast dirt road driving, of course we were aired down to around 22-24 PSI so that helped.
So what I really like about the
Teraflex Outback suspension system is how it includes their Speed Bumps. These are basically similar in function to Air Bumps used on desert racers, but less expensive and maintenance-free. If you're really working your Jeep hard at speed and hit an unexpected wash/hole/bump the Speed Bumps act like a secondary spring, slowing the uptraveling axle down and making for a smooth hit rather than an jarring hit. They're really quite impressive and work well for this kind of task.