You're actually in the wrong forum for this. No one here is an expert in modifying things that can become a major liability issue, and if they did have the answer, they wouldn't help you wreck your truck. You're attempting to degrade braking ability, cornering, steering response, and comfort. The goal of installing larger tires is what people who do off-roading are after. If you're not going off road, what is your reason for wanting larger tires? Rather than retype everything that I normally like to include to make you an informed consumer, here are copy / paste versions of some pieces of my previous replies:
The problem is most owners do not understand the ramifications of making modifications to what the engineers designed in. If a vehicle could be raised or lowered without compromising safety, the manufacturer would offer that as an option. In fact, you will find some trucks sit quite a bit higher than similar versions based on optional equipment but that is an entire package that was developed by the experts to work properly as part of a system.
You can also find trucks that appear to be lowered but that is an illusion created by adding moldings along the bottom of the body.
All cars and trucks have height specs that are published. Alignment specialists have small books that show each model, where to take those measurements, and what they should be. As an alignment mechanic there were three parts to my job. The first was to inspect the steering and suspension systems to identify and replace loose or worn parts. That included "reading" the tire wear patterns and determining what was needed to improve that wear. Next was measuring and correcting ride height. When I worked for a mass merchandiser, that commonly meant installing new coil springs on the rear of GM cars, (which was real easy and inexpensive), and on Chryslers it involved adding helper springs around the rear shock absorbers and simply adjusting the front torsion bars. The final step was to perform the alignment. Years later when I worked for a very nice Chrysler dealership I saw mostly newer vehicles and very few with sagged springs. The exception was the Dakotas that still were using torsion bars. In almost every case of tire wear complaints, the "before" readings on the alignment computer could easily be shown to be the cause of the tire wear, and the "after" readings, which were after I made the adjustments, were right at factory specs. The funny thing is though I rarely had to adjust the "camber", "caster", or "toe" with the factory-provided adjustments. All I did was raise the front end to specs by adjusting the torsion bars. As the suspension approached the proper ride height the alignment numbers and suspension geometry fell right into place. We often ended up charging the customers for an "alignment check" instead of the full alignment.
To add a few tidbits of information, your truck has what is referred to as the "short arm / long arm (SLA) front suspension. The lower control arm is the long one and from the frame it goes straight out to the lower ball joint. That arm should be nearly parallel to the ground. The upper control arm is considerably shorter and it usually angles down from the bushings to the upper ball joint. The different lengths makes them go through different arcs as they travel up and down. That causes the wheel to tip in and out on top as the truck goes up and down over bumps in the road. A long time ago a few vehicles had equal length upper and lower control arms. They found that design made the tires slide left and right across the road as the vehicle went up and down, and tires would scrub off in about 10,000 miles. With your SLA suspension the tires don't slide sideways as much, and they tip in and out on top to reduce the effect of that sliding. The system is strong and one of the best for tire wear and comfort as long as the geometry is correct, meaning ride height. The only disadvantages are it's a heavy system and it takes up room needed for the drive train on lightweight front-wheel-drive cars. That's why those use a strut suspension system.
"Scrub radius" is a designed-in angle that can not be adjusted, but it can be wrong if ride height is wrong. Imagine standing in front of the truck and looking back at the upper and lower ball joint. Draw an imaginary line through them. That line should intersect the road surface exactly in the middle of the tire tread. That will not be the case if tires with a larger circumference or wheels with a deeper offset are installed. Due to friction and rolling resistance the left half of the tire tread wants to pull to the left, and the right half of the tread wants to pull to the right. Lowering the ride height by replacing or adjusting the springs will not change that relationship but it does seriously affect the other geometry as I mentioned. Using drop spindles raises the wheel and tire so in effect it lowers the two ball joints along with the rest of the truck. Now that imaginary line intersects the road surface closer to the inside of the tire. A lot more of the tread wants to pull toward the outside and little of it wants to pull toward the center of the truck. When the left tire strikes a bump it will want to pull that way instead of staying straight. That can be very tiring to maintain directional stability on longer drives.
Where braking comes into play is when one tire momentarily loses traction from going over bumps, potholes, and even sand on the road. The two halves of each tire tread balance each other to maintain straight braking. With altered scrub radius, in the case of a lowered vehicle, if the right tire slides over some sand while braking, the left tire will pull the steering linkages to the left and you will have to counter-steer to the right. THAT is what a good lawyer will explain to a jury when he is trying to shift the blame from the guy who caused a crash. You don't want to give him that option, and no mechanic wants to get you involved in that possibility.
You also have to consider drive line angles. If your truck is a four-wheel-drive it will have cv joints on the two front half shafts. Those are designed to go through specific angles as they rotate. The inner joints have three large rollers that move back and forth about a half inch each revolution. Rear universal joints go through the same angle changes on purpose. Their needle bearings in the cups can't be allowed to stay in one location because they will wear indentations into the cross and cups, then when you bounce up and down on bumpy roads or load the truck, that angle will change and cause the needle bearings to roll across those indentations. That will set up a howl and vibration. Similar wear takes place in the front inner cv joint housing but it is minimized by those rollers moving back and forth a lot. When the angle between the shaft and joint is reduced those rollers go through a smaller change so all the wear is concentrated in a smaller area. You will likely never notice that on your truck if you don't drive in four-wheel-drive often, but when that occurs on front-wheel-drive cars it sets up a horrendous steering wheel shimmy during acceleration. Due to the engine torque the rollers bind when trying to run over the raised parts of the worn spots. That prevents the shaft from smoothly changing length as it rotates. Instead, it pushes and pulls on the spindle. Those are attached by the ball joints to the control arms which are mounted on rubber bushings that can easily flex so the moving spindle tugs on the steering linkage.
That wear can set up a severe steering wheel shimmy but it can be way too small to feel, (the wear, not the shimmy). Those rolling surfaces are polished, and the only way to identify that wear is to clean the housing, then shine a light in it and look for the slightest irregularity in the reflection. People have also run into that shimmy on front-wheel-drive cars when putting the ride height back to where it should be. Since the wear was concentrated on a smaller-than-normal area, once raised back up the rollers go through their normal range of travel and they run over those raised spots and can bind.
One last comment that most do-it-yourselfers aren't aware of is when any suspension parts are replaced that are mounted with rubber bushings, mainly the upper and lower control arms, the pivot bolts must not be tightened while the vehicle is jacked up. Those parts will be hanging down and if the bolts are tightened that way the bushings will be clamped in that position. When the vehicle is set on the ground the control arms will pivot up and those bushings will be in a permanent twist. That will greatly reduce their life. The vehicle must be lowered from the jacks so it's sitting at normal height, then the bolts can be tightened.
The smaller GM trucks eat upper ball joints like crazy. At the correct ride height there will be reduced movement through the pivoting of the ball in the socket, and reduced wear. Also, If you watch the visual "camber" graph on the alignment computer, you will see very little change as the truck is bounced up and down when it starts out at the correct height. When the height is not correct the camber will change a lot as the truck is bounced. Camber is the inward or outward tilt of the wheel as viewed from in front and has the biggest affect on tire wear. Camber can be corrected on most vehicles except many Fords, so it will look good and "in specs." On the alignment printout, but it's that exaggerated tilting while driving that causes accelerated wear to both edges of the tire tread. It will look the same as under-inflation wear and is often mistaken for that. That's why if ride height is not correct you will still have poor tire wear even though the alignment computer says the adjustments are perfect. Some of the newer computers now even make the mechanic use a special gauge to check ride height before allowing him to make any adjustments.
You've decreased the truck's ability to stop in a hurry, and believe me, lawyers know it. All cars and trucks use a proportioning valve in the brake hydraulic system to reduce rear-wheel-lockup under hard braking. You've raised the center of gravity a lot. Under moderate braking the weight is going to shift to the front more than normal. That proportioning valve is carefully calibrated to your specific set of options including engine weight, with or without air conditioning, weight distribution, and "unsprung weight", meaning axles and wheels, ... Anything not supported by the springs. The proportioning valve works on brake fluid pressure, not weight transfer, so it won't start doing its job until well after the rear tires are skidding. A lot of trucks and minivans have height-sensing proportioning valves mounted in the rear because there can be such a wide range of loading, from empty to fully-loaded, and the braking system needs to adjust for those conditions. If your truck has that height-sensing valve in the rear, how was that handled? You've changed the height in the rear twice. Did you fashion a longer link between the axle and valve twice? The adjustment of that link is critical and very precise
I CAN tell you I've had many Mopar muscle cars, and still have a '72 Challenger, and every one of them was at exactly the specified ride height. Most experienced alignment mechanics, me included, won't even touch a vehicle with altered ride height. I had my manager's approval, along with the dealership owners blessings, to refuse to get involved with any modified vehicles. We all knew that if the other guy ran the red light and caused a crash, his lawyer would convince a jury that you were partly at fault because you were less able to avoid the crash, and he would be right. We already have the threat of a lawsuit on every vehicle we work on, and we had better be able to prove our actions didn't have anything to do with a crash. Once we work on an altered vehicle, we become a party to any potential lawsuit. You could be the safest driver in the world, but that doesn't protect us from the other people on the road.
Keep in mind that automotive sales is extremely competitive, and if there's anything a manufacturer can do to build a model that will increase sales, they're going to do it. The reason they don't offer raised trucks and lowered cars is they know it can't be done while maintaining the level of safety and handling they already have. No aftermarket lift kit supplier is going to come up with something better and safer, so you know all of those characteristics have been compromised by altering the ride height.
I know there's little chance I'm going to convince you to take that stuff off and put the ride height back where it belongs. At least you are now an informed consumer so you can decide how much risk is worth having bigger tires.
This whole ride height story took up about ten hours in my 180-hour-long Suspension and Alignment class. Some of my kids wanted to alter the ride height on their cars and trucks but once they learned what would be affected no one wanted to pursue the project. We wouldn't have let them do it anyway because of liability reasons, and it is not something legitimate to be teaching.
One of my former students had previously lowered his truck, and when he got hired by the local Goodyear tire dealer, he lied and said he did it in my Auto Shop at school. That shop owner, along with the owner of the Chrysler dealership I used to work for were both on our Advisory Committee, and together they started the first-of-its-kind in the nation organization (Google "WATEA"), to promote high school to community college to work program and scholarships to get kids into our program. The roof just about blew off the school when that kid told them he altered his truck in my class. The phone lines were red hot in our city until other students assured them this didn't take place in my school. The point I'm trying to make is altering ride height is a really big deal. No one expects owners to understand how the suspension geometry works and affects all the other characteristics of the vehicle. That's our job, but it's also our job to look out for the best interests of our customers and explain why correct ride height is so important.
Okay, I'm back now. Remember those are excerpts from three or four previous replies. I need to add something about your torsion bar suspension system. I've had dozens of Chrysler products, some that I raced, (on three local racetracks), so between that and my training and experience, I know all about torsion bar systems. Somewhere in this previous novel, I mentioned the lower control arm is supposed to be parallel to the ground. The steering linkage also must be parallel to the ground to prevent the vehicle from steering left or right as it goes up and down over bumps. What I mean by that is one tire will run over a spot in the road that's just a half inch higher for a few feet. That puts a lot more weight on that tire for a fraction of a second, and it will tug unevenly on the steering linkage. Even by '97 standards your truck handles well enough that you can drive it for hours on end at highway speed without getting tired. That comfort is going to be lost because you'll be constantly making small, barely-noticeable steering corrections. Each tire is going to contribute a small "bump" to the steering wheel each time it hits a pebble or crack in the road. At first that increased "road feel" might feel like a good thing, but you'll get over that pretty quickly.
Imagine your arm stretched out straight to your side so it is parallel to the floor and your fingertips are just touching a wall. Now move it up 6" and down 6". That is what your lower control arms do on your truck as you're driving. As you go through those motions, look how far your fingertips move from the wall. Probably less than 1/4".
Now hold your arm down at a 45 degree angle and do the same thing. Move your arm up and down through the 12" range and see how much your fingertips move closer to and further from the wall. If my memory of geometry is right, that's also 12". That's an extreme example, but that's what the bottoms of your tires will be doing. The only time this doesn't happen is with a solid tube front 4wd front axle. Those trucks have their own special problems when people forget to lower the steering linkage to keep it parallel to the axle.
Trucks with coil springs in front require a lot more work to modify. With torsion bars, making a simple adjustment allows owners to do that without giving much thought to what else is changing. Even when people tell me they need the added ground clearance, they're a little disappointed when they see it's only the frame and body that are raised. A tire that's 4" taller only raises the axles 2", so you're still going to get hung up on that tree stump you want to drive over.
You also have to remember that on your truck, the front suspension travel going down is limited by the upper control arm hitting the rubber "bump stop". I don't know what you're referring to by "key", but if you can't lower the front from where it is now, what's going to happen when you drive over wavy road surfaces and the truck wants to bounce smoothly up and down? If you feel the front suspension reach the end of its travel and bottom out one time, you're going to take notice. If that happens constantly, you're going to be a very unhappy truck owner.
I know I didn't answer your question and this isn't what you wanted to hear, but if you look at how much time I put into this reply, you'll see how important this topic is. If you still want to pursue this, I can answer specific questions about how the system and its parts work, and how it affects various characteristics of braking and handling. I can tell you about some of the parts needed, but I don't know aftermarket parts suppliers or part numbers. I'll have to leave that up to the people who sell these kits.
Saturday, October 18th, 2014 AT 11:27 PM