The prerunner truck is a popular build style. If done right, they look beautiful, and deliver astounding performance. If you’ve ever built one, then you understand the complexity involved when you take a vehicle so far from what it once was. For those of you who have not, but would like to, this article will give you some insight into the evolution of a prerunner build. It will be the first of a series going over the who, what, where, when, why, and how of prerunners.
The first thing you need to do is come up with a plan. The end result will usually stray from your original intent, but if you don’t have an initial plan, you cannot budget time or money accurately. The easiest thing to do is go down to your local fab shop, write a check with many zeros, and hope to have your ride in six months to a year or more.
Since most of us can’t do that, it’s better to sit down and figure out exactly what you want to achieve. Do you want a street truck that just looks cool? Do you want a truck capable of merely driving around in the desert? Or do you want a vehicle that is capable of prerunning the Baja peninsula at race speeds for an entire season?
Planning Out The Prerunner
You have to ask yourself whether you have the time and money to continue your project to completion. Do you have a space to work? Do you have tools, and the skills to use them? Are you going to drive your vehicle during the process, or do a complete build from the ground up?
Many projects are started, but stall out because they were not properly planned out from the beginning. Once you evaluate your wants and needs, your goals may change.
You might be just as happy with a leveling kit, wheels, and tires. There is a lot to be said for the people smart enough to do a mild build, and enjoy it, instead of spending years dropping money into a garage trophy.
Another reason to make a plan relates to the best advice you will ever get about building any automotive project; do it right the first time. Most temporary fixes are just plain wasted money. If you have to do something over, you are still paying the money you thought you couldn’t afford, and the money you laid out when you went for the quick fix. That adds on a lot of cost that can be used to better advantage somewhere else.
Part of your plan must include what type of vehicle you want to build. Are you looking for a full-size truck, midsize, or something altogether different. A popular trend right now is to outfit road-going cars or SUVs with big tires, shocks, and a few off-road accessories, then hit the dirt. They don’t have nearly the capabilities of a long-travel prerunner, but it might just fit your needs.
2WD Or 4WD? You Decide
One of the biggest factors in deciding what to start with is the question of two- or four-wheel-drive. Four-wheel-drive is a real luxury. When it comes to traversing all types of terrain with little drama, four-wheel-drive takes the cake. Building a two-wheel-drive prerunner almost locks you into building something highly modified because you will be running at higher speeds, and putting more of a strain on the components. When you slow down or stop in 2WD, you are always at risk of getting stuck. When speed is your only friend, you will use all the wheel travel and traction you can muster. That means you will need beefier suspension and driveline components.
What 2WD does do better at than 4WD is saving weight and having far fewer moving parts. Generally, you are able to get much more wheel travel out of a 2WD suspension than a 4WD, because 4WD articulation depends on the maximum angle you can put on the CVs or U-joints on the front axle shafts. If your goal is to do actual prerunning, 2WD will be fine, because you will be running at high speeds most of the time. You can drive through just about anything at speed; but if you plan on stopping in the silt, mud, or sand, you will need a good shovel.
Piece By Piece: Tires And Fiberglass
If you can save your money and do it all at once, that’s great, but most of you will need to build in stages. There is a popular saying that goes with automotive projects about a snowball rolling downhill, and it’s true. As the snowball rolls downhill, it gets bigger and bigger. The same will be true with your build because everything that you do affects everything else. Vehicles are engineered from the factory to perform in a certain way and once you upset that, there are consequences.
The first priority is tires. Your tires are the only connection your vehicle has to the dirt. Good tires that are capable of taking some punishment from rocks, and other environmental factors are a must. You will have to assess the ratio of on-road to off-road travel you will be doing. All-terrain tires perform better on pavement. More aggressive tread patterns perform better in the dirt, but might be noisy on the pavement and grip less on wet pavement due to the voids in the tread.
What size tire will clear the fenders, and how much the overall diameter will affect your gearing, will determine what size you can run. The larger the diameter of the tire, the harder it is to start or stop. Increasing the diameter will also affect your turning radius. Most factory wheel openings are not very accommodating to bigger tires, and the rear typically has more clearance than the front. “Self-clearancing” is bad for both the sheet metal and your tires, so take the time to do some trimming before you experience damage.
If you are also upgrading the wheels, it’s important to get the offset and diameter right so you don’t put undue stress on your wheel bearings, negatively affect your scrub radius, or create interference with your brake components. Bigger tires will increase your unsprung weight –the weight of your suspension components – so your stock shocks will no longer be up to the task.
Piece By Piece: Springs
Your project will ride on some type of springs whether they are coils, torsion bars, or leaves. Torsion bars and coils operate the same; leaf springs are unique.
Springs have a number of factors that determine their spring rate, which is the amount of force required to deflect a spring one inch. Standard coil springs have a linear spring rate. That means if the spring rate is 500 pounds, it will take 500 pounds to compress it one inch; 1000 pounds, to compress it two inches, and so on. On the other hand, leaf springs have a progressive rate. As they compress, the spring rate increases. Leaf springs pull double duty by carrying the load and locating the axle. In rear truck applications, their progressive rate works well – as you load cargo into the truck bed, the weight increases, compressing the springs. As that load compresses the springs farther, the spring rate increases to compensate. The job of your springs, regardless of the type, is only to carry the load of your vehicle. Controlling the movement of the suspension falls on your shocks.
Piece By Piece: Shocks
Thanks to racing, shock technology has reached a high level of sophistication. When you break it down to basics, shocks dissipate kinetic energy by using friction to create heat. They are filled with thick oil that flows through orifices in the piston, and/or in bypass openings. By controlling the flow of fluid, you control the movement of the shock. Shocks can also be used as a coil carrier to combine the spring and the shock together in a single component. They are called coilover shocks.
The other type of shock commonly used on prerunners is a bypass shock. A bypass shock has additional passageways for oil to flow through. By changing the location of the bypass passage, you can control motion in specific zones according to shock shaft position. These shocks are known as position-sensitive shocks. The passageways can either be internal or external to the shock body. To muddy things up, coilover shocks may also contain internal bypass technology.
Shocks with external bypass tubes contain adjustable valves that allow you to control the amount of fluid that flows through the passageway. Bypass tubes can control both the compression and rebound strokes of the shock. This gives you an incredible amount of control.
Another form of shock adjustment is the use of compression adjusters. These control the flow of fluid in and out of the reservoir. Reservoirs may be mounted to the shock body, or remotely. The reservoir has a floating, solid piston inside. A charge of nitrogen is introduced on one side of the piston to exert pressure on it, and hence the fluid. This prevents the fluid from mixing with any air, as air in the fluid reduces the effectiveness of the shock. Compressing the shock fluid will increase the point at which it will boil; reducing shock fade. The reservoir gives the shock fluid room to expand when it gets hot, and contains the fluid that gets displaced by the shock shaft when the shock compresses. Slight adjustment to the shock valving is possible by changing the charge pressure in the reservoir.
Performance shocks can also be taken apart for rebuilding or to modify the piston valving. The valving consists of shims that are made in varying thicknesses and diameters. The shims cover ports in the piston, and flex open when the fluid is pushed through the ports. Performance shocks are constructed from high-end materials to exacting dimensions. That’s why they cost substantially more than generic shocks. Since a prerunner’s suspension is so important, good shocks are crucial to the vehicle’s performance.
Thanks to the automotive aftermarket, there are many options available that bolt directly to your truck’s existing suspension mounts, meaning you can experience enhanced suspension performance without doing any fabrication work. Bilstein, Fox, King, and others have direct replacement shocks that are substantially better than the factory offerings.
As an example, Bilstein’s 2.65-inch diameter B8 6112 has additional oil capacity that helps cooling, increases damping potential, and provides long-term durability. Like many of the coilover factory replacement shocks, it bolts to the stock mounting assembly and allows slight ride height adjustments to level the front end. Aftermarket bolt-on shocks are a simple and effective way to get enhanced performance without sacrificing the factory ride.
With good tires, performance shocks, and a traction aid like a limited-slip or locking differential, you’ll now have a vehicle capable of getting around the desert – but you are probably still limited to slower speeds. In order to reach the next level of performance, you will have to take the next step which entails cutting into your cab, and doing custom fabrication. Stay tuned for part two of our series, where we will go over the next steps in prerunner builds – advanced prerunners.