Wes at Trail Jeeps was explaining it to me. Not sure there's an actual spring but the idea was that without a pass through, the pressure would be uneven between the two sides and, thus, always pull a little to the left. This is the fundamental reason people go for dual stabilizers, so they even each other out by pointing in opposite directions. Rather than doing dual, you could just buy the one with the pass through. (I've extrapolated more based on some research I did after talking to Wes so may be best to discuss with him before purchasing and make sure this is all accurate).
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http://wayalife.com/showthread.php?p=621404
Hey Guys! Sorry we're a little late to the thread. So, steering stabilizers can be surprisingly tricky on JKs, there are a lot of variables, maybe I can help by sharing our experience.
One thing that is always true is that a steering stabilizer is not there to make your Jeep "drive better." It should never be used to mask damaged, improperly installed components or bad steering geometry. The steering stabilizer is there to do exactly what the name implies: to"stabilize" the steering by keeping feedback from the road from reaching the steering wheel. It should "smooth" out the road feel and keep those little lines in the pavement from causing your wheel to wobble. It will also absorb some of the sharp impacts from the road from reaching the steering box in full, helping to save a little bit of wear from the mechanical components of your steering system. We do not recommend driving around without a steering stabilizer long term as it will accelerate wear on your steering components. If you have a wobble, vibration or twitchy steering before adding a stabilizer, something is wrong with your Jeep, and by not addressing it you are giving it the opportunity to continue to wear, fail, or present itself in a more extreme situation that it would without the stabilizer (like catastrophic failure on a bumpy freeway overpass doing 70 miles per hours, instead of something you notice on your way to the neighborhood grocery store, for instance).
The factory stabilizer should be adequate up to a "small" 35x12.50 tire. It is worth noting that a stabilizer on the tie rod does theoretically save the tie rod ends from a little bit of wear and does a better job at "stabilizing" because it's closer to the source of the feedback, eating up feedback before it passes through the tie rod and drag link.
Ideally, a single high quality stabilizer on the tie rod should do the trick for most situations. As mentioned in the thread below, a gas stabilizer is a one way shock and can cause a slightly pull if slightly over pressurized. Fox is notorious for inconsistent stabilizers. A single Fox Adventure or Performance series 2.0 does a great job for most applications, although the magic formula is a properly dialed Fox ATS stabilizer, which is the pass through designed mentioned in the thread. Its two way design should guarantee even performance and you can adjust the pressure the stabilizer applies to the steering system. They're expensive, but worth every penny. Occasionally you get a "sticky" ATS that will cause your steering to feed twitchy because you're constantly over correcting.
Speaking of twitchy, the potential for twitchiness is one of the primary reasons for not running a dual stabilizer. Just like a sticky ATS, a dual gas setup will often apply too much pressure to the steering system. A dual stabilizer consistently works well in an old school hydraulic set up (see those old school set ups full-size Chevy's used to run in the 80s) because they only provide resistance to the steering system, not constant pressure. But, by the time you do all that, you might as well invest in a gas stabilizer which is simpler, cleaner and is more high clearance and doesn't leave you with a bunch of junk hanging out under your Jeep.
We are obviously a Fox dealer and push Fox. While there are inconsistencies, the Fox stuff does a great job for us and our customers. There are other, great choices out there as well! It's all about choosing what's right for you.
In the end if you're looking at the best solution, we will always recommend shelling out the dough for a Fox ATS and calling it a day.