HMS Beagle wrote:
With a live rear axle, 11" at the wheel is 11" at the spring/bag.
Good luck getting 11" of vertical travel out of both wheels at the same time, which is required on a live axle to make the spring and wheel travel the same amount.
I used to do a bit of 4wheeling and rock crawling and had some custom suspension setups on my rigs. I would get 19" of wheel travel, but only when one wheel was stuffed and one was drooped, the spring rate increases too much to get the full travel out of both tires in the same direction at the same time. Off road shock setups are also not designed around full compression or extension of both shocks at the same time, but articulation. I ran shocks with 12.875" of travel and my 19" of wheel travel was limited by the springs and not the shocks. A 6" bag will give more than 6" of useable travel in nearly all conditions. The bags used on the Dodges have just under 6" of travel, more than enough for the OEM suspension.
Spring rates on the lighter 3/4 Dodge pack are 2600 lb/in, your not going to get full travel on both sets at the same time without racing thru whoops.
The axle also rarely moves both tires at the same time when driving off road, usually one side moves more than the other.. this is why 6" of potential travel at the bag makes for a bit more than 6" at the wheel, keeping your traction and stability and not reducing useable travel.
About the only time one has to worry about airbags limiting travel with stock shocks and springs is when lifting the vehicle off the ground by the frame.
