Sometime ago, I visited a suspension especialist and went for a ride on a long travel suspended race truck... wow... what a ride....

PARTS NEEDED:

• Sway-A-Way RaceRunner shocks (heim-joint) with remote reservoir and coil carriers: 10" travel in rear and 12" travel in front.
• Eibach coil springs: front = 350 (12") and 350 (14"), rear = 700 (8") and 900 (12").
• custom fabrication by Donahoe Racing, the front top mounts are all 100% bolt-on.
• travel limiting straps in the front. You'll need this as the panhard rod forces the axle to swing to the driver's side when articulating.
• bent trailing arms (optional)

After playing a bit with the forklift, i got the measurements (32 inches of vertical) and estimate about 936 for the RTI.
The front springs were a bit stiff. You may notice in the pictures bellow that the front tire is not tucked in as the rear. More adjusting needed.
The droop on the rear wheels is very limited by the trailing arm link. Heim joint or bent trailing arm is next. The front can be improved a lot more. Some more thinking to be done. That is also next...

On the usual trail I go to, I chose some spots where I always lifted the tires. And this time, the suspension worked like a charm. No air under the tires, no spinning wheels. Just a smooth climb over the obstacle.

Later to find out that there are trails that will still make it lift a tire. So the "long travel" suspension does have limitations.

RTI ... 956. I can conclude that the front spring rates were a bit too stiff. when reverse, most of the weight of the vehicle is on the front springs, resulting in better articulation. I think spring rates are crucial. There must be a good balance between the front and rear.
The formula below (forklift method = 936) proves to be pretty good to the actual number.

Special thanks to Mike Duncan @ Four X Doctor for letting me use the ramp.

Some info on RTI:

If you have access to a fork lift, you can determine the RTI:

• Lift the tire just before the other tires get off the ground.
• Measure the vertical distance (h) from the bottom of the tire to the ground.

let's say you get h = 25 inches. and that the wheelbase is 92.9 inches (D90).

RTI = (h/0.34202)x1000/wheelbase.

RTI = (25/0.34202)x1000/92.9 = 787
of course, it's not very accurate, but you get the idea.