2012 Jeep Wrangler: RTI Ramp Trips #4 and #5 (Mopar Stage III Suspension With Stab On, Stab Off)
February 23, 2012
With the addition of the Mopar Pre-Runner Stage III Suspension System, a 3-inch lift kit, our 2012 Jeep Wrangler Sport is fast approaching the limit of our 20-degree RTI ramp. But not quite yet.
The smidge of daylight under the left-rear in the above pose indicates this shot was taken just before I backed it down the ramp slightly to find the official measurement point where the BFG rubber barely kisses the concrete.
This time I made the measurement two ways: once with the front stabilizer bar connected and once with it disconnected.
The results were surprising.
You'd think that three inches of lift and remote reservoir shocks would add up to a healthy bump in measured suspension articulation. With the front stabilizer bar disconnected, at least, you'd be right.
So configured, our lifted Wrangler produced 29-5/8" of left-front wheel lift, a number that corresponds 86-5/8" of progress up our 20-degree ramp. That works out to 908 RTI points when compared to our 2-door Jeep's 95.4-inch wheelbase.
The same measurement was 820 before I installed the Mopar Stage III kit.
But a funny thing happened when I measured RTI with the front stabilizer bar connected: It was worse. And by that I mean worse than the stock un-lifted suspension with the front stabilizer bar in the same state.
With the bar in full effect, the Stage III kit hiked the front wheel 18-3/32" and generated an RTI of 564. The stock suspension allowed 20-7/16" of lift and 626 RTI points.
How can this be?
Turns out, the Mopar Stage III kit employs springs that are not only taller -- they're also stiffer by about 25 percent. Articulation is limited by roll stiffness, and roll stiffness is generated by the stabilizer bars and the springs. For a given stabilizer bar size, stiffer springs produce more overall roll stiffness. And so the stiffer stage III springs restrict RTI somewhat when the stabilizer bar is connected.
But the stabilizer bar still represents the lion's share of the roll stiffness, and when it is disconnected the stiffer springs don't produce enough to limit articulation on their own.
And so we see pictures like this...
The front spring is impressively compressed, but there's still a fair amount of daylight.
We may yet be able to squeeze more RTI out of this suspension. After all, we have not yet disconnected the rear stabilizer bar, and we have not yet played around with tire pressures on the RTI ramp. We may yet get to 1000 -- or beyond.
But we will probably have to institute our Plan B for the RTI ramp before we cross that threshold.
Dan Edmunds, Director of Vehicle Testing @ I forgot to check miles