This is from Ron. He couldn't have stated it better.
I'm starting to notice a large influx of newbies inquiring about lifting their jeeps around five to six inches. I'm wondering why you all desire this lift height and what you plan on accomplishing by doing so (ie. what size tires you want to run, specs on your lift/drivetrain, type of wheeling you plan to do).
The reason I ask is because, in my opinion, a 5-6" lift on a grand with short arms and stock axles/driveshafts is a very poor setup. This can be done but, the cost goes up!
Do you want to lift your ZJ 5-6" to fit a specific tire size? Do you realize the consequences on the drivetrain as a result of running that tire size? I'm guessing that most people who want to lift their grands this much are planning on running 33-35" tires, and that lift height/tire size is a wonderful combination that will likely not require excessive fender/bumper trimming and/or rediculously extended bumpstops. HOWEVER... to SAFELY and RELIABLY wheel on 33-35" tires, the axles will need to be regeared (especially if you have a 4.0L w/ 3.55:1 gears), or better yet, completely replaced with stronger axles capable of handling the loads that these bigger tires impose upon them. I swapped out my stock axles because I kept breaking them every time I went wheeling with my 33" tires...and even when my rig wasn't being wheeled, I was going through hubs and balljoints like crazy. I have ~4500$ in axle parts from doing my axle swap, and it would've cost a lot more had I not done all the work myself and made every single little bracket from scratch.
Control arm angles are another thing to consider. Anything above about 4" of lift makes for noticeably steep control arm angles. These steep angles suck because they do not allow the suspension to work properly. As the control arm angles get steeper, their bushings start to become the absorbers of vertical movement of the axle, which is supposed to be absorbed/dampened by the shock absorbers. Also, everytime a bump in the road is hit, the front axle not only travels up as usual, but it's also now forced to travel forward following the arc of the control arms pivoting at the frame...the more severe the CA angles, the more forward movement the front axle is forced to make when a bump is hit. This is not really a factor for the rear axle, as it is forced backwards when it goes up...which is much easier for it to do as the vehicle is traveling forward. Taking note of this should make it easy to understand why steep CA angles result in poor ride quality.
Another thing to think about with a 5-6" lift is poor steering geometry. The inverted "Y" design of the stock ZJ steering works very well at stock ride height since the tie-rod and drag link are relatively close to parallel. As the vehicle is lifted, the tie-rod and drag link become more perpendicular. Due to the geometry of the inverted "Y" steering, the toe of the tires will change significantly when a bump is hit if the two links are not close to parallel. If you can't visualize why this happens, make a quick model of your stock steering with a couple pencils and notice how the ends of the links where the steering knuckles would be move together and apart as the "ride height" changes via the mock pitman arm. The rapidly changing toe angles of the front tires after hitting a bump is a primary source of the dreaded deathwobble.
Have you thought about driveshafts? Odds are good that with 5-6" of lift and stock axles, you will have a very difficult time adjusting the caster of the front axle correctly without introducing terrible vibrations from the front driveshaft. With a double-cardan style front driveshaft, the axle pinion should be pointed directly at the transfercase...if it is not, the driveshaft will likely vibrate like a *****...which will not only annoy the crap out of you, but it will also quickly wear out your driveshaft U-joints, pinion bearings, and transfercase output bearings (these vibrations may also result in female passengers reaching orgasm while riding in your jeep, but we all know the female orgasm is only an urban legend anyway). So since the front axle needs to be close to its stock orientation to maintain decent caster, the pinion will not be able to point at the t-case like it needs to.
The rear driveshaft is not as much of an issue as the front axle if adjustable lower rear control arms are used. Adjustable/longer control arms will allow you to rotate the rear axle back to a "level" (stock) position, and will result in proper d/s angles so that vibrations should be minimal.
There are several other things I could go into detail on, but they're not quite as significant as the issues stated above.
But basically what I'm trying to make a lot of you realize is something I've stated several times before: you can lift a grand to about 4" very easily, safely, and inexpensively...but lifting it the next couple inches is a huge step that opens a huge can of worms that will likely cost you a small fortune.
So if you are a newbie to wheeling grands and are curious about lifting it, I'd strongly recommend you keep it at 4" or less lift and 32" or smaller tires unless you are very dedicated to working on it and wish to spend obscene amounts of money on it to make it drive and wheel properly. Keep It Simple Stupid!
If ya'll don't understand some part of this or need further clarification on anything, or disagree with anything I've written, speak up and I'll gladly address your concerns.
I copied and pasted that from here http://www.jeepforum.com/forum/f13/z...u-post-880249/
welcome to the forum, you're in the right place, you'll learn a lot. after doing some research and looking through the picture threads you can probably get away with what you're looking to do with one of the 3.5'' kits. 6'' seems like the most popular height for a lot of other rigs, chevy, toyota, ford, dodge, nissan, but Jeeps have superior/legendary off road performance so you often wont need to go as high as you think to achieve the desired results.