Before your add a Leveling Kit or Lift Kit and Larger Wheels and Tires
First off I want to start with how to get correct final ratios. Remember that for most trucks was a 265/75 R16 tire... Like my truck came with 265/75 R16 tires even though the door sticker states 245/75 R16. The 245/75 R16 was used in the early 24V body design. The most common axle is 3.55 gears. If you are going to use a larger than stock tire makes sure to have 4.10 gears. Its a REQUIREMENT!
Final Ratio Goals
Let me just state you aiming for a final ratio of 3.55 to 3.73 which is the most optimal for power and economy.
Let's just show how just a small jump from 265's to 285/75 R16 turns the final ratio. This will now create a final ratio of 3.42:1 which is a marginal you could use it but optimally it will add more EGT's and higher engine loads. The more you keep increasing the tire size it will drop the final ratio too low. For example, going from 265/75 R16 to 37 x 12.50 R16 you are now at 3.04 for the final ratio. Again you cannot install large tires on a 3.55 geared axle. This combination is going to create super high EGT's and high engine loads so the power is greatly reduced and the EGT's will sore well past 1,200*F. Another wanting to run oversized tires should consider installing 4.10 gear for everything up to 37-inch tires. This again impacts even tuning with the Quadzilla being you are going to require a large drop in timing more retard timings just so the turbo will spool quicker.
The tool I use to find the final ratio to the ground.
Me personally, I ditched the 265/65 R16 and opted for the 245/75 R16 being that gives a final ratio of 3.69.1. Cruising at 66 MPH is just about dead money at 2,000 RPM. At 82 MPH you are at 2,500 RPMs. This is a good ratio. I've gotten many trips to Boise down the I84 interstate at 80 MPH and cleared 20 MPG commonly. I'm also NV4500 transmission (0.75:1) where a 47RE transmission is lower yet at (0.69:1) these should be a touch lower in RPM. The NV5600 is close to the NV4500 at (0.73:1).
Now a lot of people don't know but just adding a 1-inch lift to a 2nd Gen truck will screw all the angles up in the axle. Even the 2-inch lift will do it even worse. The problem is the axle is swung on 4 control arms. When you add lift to the axle you are swinging the axle downwards as it swings down more the control arms are fixed and the axle rolls forward more which now makes for a more neutral caster angle. This could be corrected by install adjustable control arms on the bottom this would allow you to recover most of the caster angle. Then as you lift or level the front axle the track bar is a fixed length since its farther from the frame the track bar will pull the axle to the left side some this now enhances the thrust angle to the left. Between these two angles, you now created a truck that has poor centering on the highway and darts. Then the thrust angle is off it will tend to pull left. You could install an adjustable track bar to correct the thrust angle.
Wide wheels tend to place a lot of stress on the wheel bearings and ball joint being most have quite a bit of offset having the wheel poking out of the wheel well. Being you've added a long lever to pry against the bearings and the ball joints. In any case, you are going to add a lot of load on the steering box. I recommend using the standard ratio steering box. This is a lower gear ratio steering box and makes it easier for the box to steer those wide tires and reduce stress.
I highly recommend that you find a good alignment shop that does not work out of a book someone that understands the lifted truck and the needed angle changes to make a stable ride.
The larger your wheels and tires, the more mass you have in the wheels the more it will take to get the axles rolling. The rule of thumb is for every 1 pound of rotational mas you remove is like 8 pounds off the frame. To show this you might remember the park where those big merry go rounds.
Like this one, you could get about 2 or 3 kids to pull it around. Bigger the Merry go round got the more kids you needed to get it up to speed. Maybe even a few adults to help out. The point is the more mass in any rotational part is going to take even more power or energy to get it spinning and even more to hold the speed up. I've studied this on many trucks and driven plenty of oversized trucks too. No matter what larger tires do come at a cost of loss of power and lowered MPGs. The only way to make it better is to ditch the weight. which most after spending a small fortune outfitting with new wheels and tires. Hence why this article is to warn most of what you coming into. Being this weighed load is there you find that EGT's are going to be higher and the engine loads to maintain speed are higher.
Example of this in real life. I went to a dyno event with my truck back in 2006. All I had was stock injectors and Edge Comp. I was green to the whole dyno event but rush to get in line to run the rollers. One I ran the rollers I had 381/831 on my dyno sheet. Now my buddy with a 96 Dodge 12V jump in and ran the rollers came up just short 362/825. I gave him a big load of crap over it. He requested to get off the rollers after his first run. He pulled out in the lot and pull the outer two dual tires off and got back up on the rollers grinning. I didn't know why. Now I know why after shedding the rotational mass of the outer dual wheels and ran on the inners alone and surpassed me in power. He had a net gain of about 28 HP gain which gave him the win at 390 HP.
Another example at the same dyno shop different events. I have seen a jacked-up Ford on the rollers and barely made 260 HP with 37-inch tires. Then he rolled off the rollers and took off the 37-inch tires and put on stock 31-inch tires and well in the 400 HP range. Again larger tires do limit the power to the ground. Looks cool but steals the power from getting to the ground.
As for my own truck I never used any leveling kits or lift kits its complete stock. I've changed only one set of ball joints at 180k miles. I bought some cheap ball joints off of RockAuto years ago and now over 250k miles and still running those ball joints. OEM Tie Rod Ends lasted for 350k miles and was replaced only once. As for the track bar, I'll admit will all the offroad driving I manage to typically wear them out at about 100 to 150k miles for a NAPA track bar. I've replaced a few. Brakes wise I go upwards of 200k miles for a set of brake shoes. Yes, I have an exhaust brake and use it every day. With running the optimal ratio that I am I shaved off at least...
- At least -100°F in EGT temperature.
- At least -30°F in transmission temperature.
- At least 5% engine load reduction.
- At least +2 to +3 MPG gain.
- Most suspernsion parts lasting 200k miles.
- Lower Differential temperatures.
- More power produced at lower RPMs.
Never had a single case of death wobble, never had any tracking issues or sloppy steering. I'm currently at 421k miles at the time of this article.