Nitro 4-Tec Performance Guide

Tweaking the Performance of Your Nitro 4-Tec. Part I

The Nitro 4-Tec is definitely a fun machine with its TRX 2.5 Racing Engine™ and two-speed transmission. Blasting the Nitro 4-Tec™ across a parking lot at speeds exceeding 60mph is a thrill no one can forget. Although many people are content with just making insane speed runs back and forth with this nitro-powered bullet, the Nitro 4-Tec is also a very capable track performer. With a few accessories and proper set-up techniques, you'll be knocking out some pretty fast laps at your local raceway. The format of this guide will be similar to the Maxx and Revo series of articles, where I separated the guide into three categories. In this first article, I'll cover tips for tuning the suspension of the Nitro 4-Tec. Be sure to stay tuned for the following articles that will cover critical setup and building tips for the Nitro 4-Tec, and also tips on adjusting the drivetrain and tuning with tires. These setup tips and performance upgrades are not only useful for racers, but will also be beneficial for just ripping around a parking lot. Let's get started!

Suspension Tuning

Shocks

Shock springs do more than just handle the imperfections on the surface of the track; they also reduce or add chassis roll in the corners, playing a large part in how quickly the car reacts to steering input.Installing firmer springs on the shocks make the car more sensitive. If you install softer springs, the car will be a little more "lazy" going into the corners. Softer springs will give you a little more time to correct the chassis if it gets out of shapeare more beneficial on a slick or bumpy track.

Shock Oil

I recommended soft springs for new racers, or for racers who are a little "rusty." Once you've honed your driving skills and your hand/eye coordination gets quicker, try switching to firmer springs. The stock springs are a medium/soft rate, which are excellent for parking lot racing and low traction racing conditions. Check your local hobby shop for all of the optional aftermarket springs that will work with the Nitro 4-Tec.

Shock oil dictates how fast your shock shafts move in and out of the shock body, which is referred to as the "compression stroke" and "rebound stroke."

Lighter viscosity oil in the shocks will allow the suspension to react more quickly to bumps on the track surface. This will also cause more chassis roll in the corners, a lot like the way softer springs do.Weather conditions also have an effect on the damping effects of the suspension. Warm weather typically causes the shocks to move quicker. If the temperature outside is considerably hotter than the last time you ran, you may need to run thicker oil in the shocks to get them to work the way they did before.

Shock Length

A good starting point for the Nitro 4-tec Big Bore shocks is 60-weightwt oil with two-hole pistons all around. You may need to adjust this for your particular track and weather conditions.

The most important thing to remember about shock length is to keep them the same on both sides of your car. The Nitro 4-Tec does not have adjustable down stops built into the front suspension. To limit the down travel of the suspension in the front of the car, you have to limit the length of the shocks to get the desired down travel.
It's important to allow the rear shocks to extend as long as they need to. This will give a full range of down stop positions. (See "down travel" below for adjusting the length of the shocks).

Shock Position

There are two mounting holes in the front and rear suspension arms of the Nitro 4-Tec. The outside holes make the suspension more progressive as it's compressed, giving the car a firmer feel. The inside holes allow a little more chassis roll in the corners. Keep in mind, this is a fine tuned adjustment and will not give you big results. It should be one of the last adjustments once you're at the track. For most track conditions, I recommend starting with the shocks mounted in the outer positions.

Wheel Angles

Camber

Camber is the angle of the wheels in relation to the surface, while looking at the front or rear of the car.


If the top of the wheels are pointing toward the inside of the chassis, this is called negative camber. If the top of wheels are facing outward then, this is called positive camber and, of course, if they are standing straight up it is set at 0-camber.

Camber is measured in degrees. A good base starting point for camber on the Nitro 4-Tec is 1 degree up front and 1.5 degrees in the rear. Camber is normally adjusted to make the tires wear evenly. It's also used as a tuning tool.

Camber is easily adjusted by changing the length of the upper suspension link on the front and rear of the car.

Typically, more negative camber equals more traction (to a point), so if you're looking for more bite in the front or the rear of the car, then dial-in more negative camber (this is a finely tuned adjustment). Once your tires are wearing evenly, make small adjustments one way or the other for the desired traction.

Caster

Caster is the angle of the axis that the front hub carriers pivot on, when looking at the side of the chassis. More caster will allow more weight to be transferred to the front of the chassis off throttle or under braking. This promotes more steering. While under throttle, the weight is shifted to the outside rear tire providing more traction from this tire to pivot the car around the corner more easily.

To adjust front caster, simply move the caster spacers located on the upper suspension pin next to the upper suspension arm.

By moving the spacers to the rear of the arm, (pulling the arms back toward the rear of the chassis, on the left) you are adding more caster, and you should get more steering from the car. By placing the spacers toward the front (pushing the arms toward the front of the chassis, on the right) you reduce the caster and will take some steering out of the car. This usually makes the car a little easier to drive and less sensitive out of the corners.

Start with all of the shims placed to the front of the arm then move one shim at a time, from each side, back to the rear as you need more steering.

Re-active Caster

Re-active caster is adjusted by using the re-active caster wedges (part #4334). By changing the angle of the upper suspension mount, the caster will change as the suspension is compressed. Remember, if you are using the three-degree upper mount and a zero-degree lower mount, you already have re-active caster built-in. By placing the thicker side of the wedge to the front, the caster angle will rise as the suspension is compressed.

Three-degree front upper suspension mount (stock)

Placing the thicker side of the wedge toward the front of the chassis will increase caster as the suspension is compressed. Placing the thicker side of the wedge toward the rear will kick up the backside of the upper suspension mount. This takes away caster as the suspension is compressed. There is also a zero-degree lower suspension mount (part #4329) available for the Nitro 4-Tec. It takes away more steering (for smooth and extreme high-bite conditions).

Three-degree front lower suspension mount (stock)

The use of caster wedges is a fine-tuning adjustment that should be one of the last items to adjust. A good base starting point for re-active caster the stock three-degree lower suspension mount, stock three-degree upper suspension mount and the Nitro re-active caster wedges. Use the wedges as they're described above as needed.

Toe angle - in/out

Toe is the direction the wheels are angled in relation to the centerline of the chassis while looking from above the chassis. Toe settings are measured in degrees, and are measured independently front and rear. Toe-in is when the front edge of the tires point toward each other. Toe-out is the opposite, when the front edge of the tires point away from each other.

Front

Toe-in: More straight-line stability with a less sensitive response to input. This allows the car to be more drivable on the straightaway with a little less "instant steering."

Toe-out: Less straight-line stability with a more sensitive response to input. This makes the car twitchy on the straightaway, but offers more "instant" steering for tighter tracks.

Rear

Toe-in: More stability under throttle. This helps keep the rear end of the car under control during acceleration, but it also takes out some steering.

Toe-out: Unstable under throttle. Toe-out is not used in racing set-ups because of the very unstable characteristics it produces. It creates an incredible amount of turn-in, and renders the car virtually uncontrollable under throttle.

A good starting point up front for the Nitro 4-Tec is zero-degrees, then adjust in or out according to what's needed. In the rear, the 2.5-degrees hub carriers are typically used. The zero-degree carriers are not used in racing conditions. Some aftermarket companies offer different angles for the rear hub carriers. Start with the 2.5-degree rear carriers, then decide what's needed for current track conditions.

Ride Height

Ride height is adjusted by adding or taking away spring pre-load spacers on the shocks. Important: Do not use the length of the shock to determine ride height. This will make a very twitchy and unpredictable car. Also, do not use extra pre-load spacers to give the shock a firmer feel. If you want to firm-up the suspension, use a firmer spring. Pre-load spacers are only used for adjusting ride height. Generally, it is best to run the chassis as low as you can without causing contact between the chassis and the track surface.

Measuring ride height is easy. Digital calipers, or even a ruler, can be used.

Smooth surfaces will allow lower ride height settings and bumpy tracks will need a higher stance. A good all-around starting point would be about four millimeters in the front and rear for smooth surfaces and five mm in the front and rear for fairly bumpy tracks.

Weight Transfer

Sway Bars

Traxxas offers a front and rear sway bar set (part #4875) for the Nitro 4-Tec. Sway bars are essential for fast lap times on smooth high-bite surfaces. The sway bars are adjusted by placing the eyelets in the bars that pass through in one of four positions. The positions farther away from the pivot point are softer than the positions closer to the pivot.

Sway bars effect chassis handling a lot like springs do. The softer settings allow more chassis roll in the corners, and produce a less sensitive, more drivable car.For quicker response and a flatter chassis in the corners, stiffen the sway bar settings (use the eyelets closer to the pivot point). A good starting point is the softest position (farthest away from the pivot point). The photos above show the bars set in the softest position.

Down Travel (Droop)

Down travel is the distance the suspension arms travel as you lift the chassis off of the ground. Down travel, down stop, or "droop", is measured by the distance between the bottom of the outer end of the suspension arm and the ground or surface the chassis is sitting on (with all wheels removed).

Rear down travel adjustment

Down travel of the rear suspension arms is set by threading one 3x8mm set screw into each of the holes molded into the rear suspension arms (shown at left). Thread the set screws so they exit the bottom of the arm (shown at right). The screw will contact the chassis stopping the arm from falling any farther. By adjusting the set screw up and down, the down travel of the suspension will change. Turning the screw clockwise will decrease travel, and threading the screw counter-clockwise will allow more down travel.

To measure rear down travel, remove all of the shocks and sway bars so the chassis sits flat on the set-up surface. The arms should be able to move freely and fall down to the position in which they are set to fall. A good starting point for the rear is about six mm from the surface to the arm (see photo below). More down travel for the rear will allow more weight to shift to the front giving the front more bite off throttle.

Front down travel adjustment

The front of the car does not have a down stop adjustment independent from the shock. The length of the shock will dictate how far the arms will move downward. It's very important that both of the front shocks are the same length.

Check the front down stop by mounting all shocks and wheels, but without the sway bars and set the chassis at the desired ride height. After pushing down a couple of times on the front and rear of the car compressing the suspension and allowing it to come back up (to the desired ride height), lift the front of the chassis (in the center) and check how far the arms fall before the wheels leave the surface. A good starting point is to have the outer edges of the arms drop around two mm-to-three mm. Also, make sure that both arms drop the same distance when lifted. The more down travel that is allowed the more chassis roll that will occur. More down travel up front will give slightly more bite up front on throttle.

Adjusting the length of the shocks can be accomplished by threading the shock end up and down on the shock shaft (shown at left). Never allow more than one mm of thread to show above the shock end. Any more will allow the piston to rise too far up into the shock body causing damping problems.

Limiting the length of the shocks can be achieved by placing three mm I.D. spacers on the shock shaft (within the shock body) under the piston (shown at right).

Roll Center

The rear roll center on the Nitro 4-Tec can be adjusted by positioning the rear camber links in a variety of different holes. The upper holes on the bulkhead will make the car easier to drive, the lower holes will increase steering and response (start with the upper/inner position on the bulkhead). The inner holes on the bulkhead will change the camber curve less aggressively, while the outer holes will affect the camber more aggressively. Only use the upper holes on the rear hub carrier. The lower holes can make the car too unpredictable in the corners.

All of the cool accessories you see in this set-up guide are featured on the Nitro 4-Tec accessories pages.

Critical Setup and Building Tips for the Nitro 4-Tec

Another very important part of making fat and consistent lap times on the track is taking the time to build (or rebuild) your car the correct way for smooth operation and consistent performance. In this segment, I'll show you the way to rebuild and prepare some of the more important components on your Nitro 4-Tec.

Shock Assembly

	The Traxxas Big Bore shock set (part #2658) for the Nitro 4-Tec offers smooth operation and long lasting durability. The Big Bore shocks in this article are equipped with the optional Titanium Nitride-coated shafts (part #2765T) to resist shaft wear. Follow the instructions below to get the most out of your Big Bore shocks:
	Before inserting the shock shaft through the bottom of the shock body, pre-lube the o-rings with shock oil. This will allow the shock shafts to operate better (smoother action) and will also prevent damage to the o-rings.
	Next, fill the shock body with shock oil (allowing room for the shock bladder). Move the piston up and down slowly, allowing all air bubbles to emerge from below the piston to the top of the shock body. Let the shock stand (fully extended) until the shock body is rid of all air bubbles.
	Now, install the shock bladder into the shock cap and apply a small amount of shock oil around the outer ring of the bladder (to prevent tears). Thread the cap on the body until it is snug, do not over tighten the cap (damage to the bladder may occur).

Push the shock shaft up into the shock body, and then release. The shaft should go all the way up to the shock end, and then should come back out slowly. Make sure both shocks on each side of your car have the same amount of shock rebound. It may take a couple of tries to get these results, but a little practice will make it easier. Before installing the shock springs and collars, make sure the left and right hand shocks are the same length. This is very important for proper performance

Pro Ball Differential Assembly

The Traxxas Pro ball differential (part #4840) for the Nitro 4-Tec is one of the first accessories I recommend getting for racing. The Pro ball diff is very smooth and easy to use. Adjustability of the front and rear differentials is crucial for maximum performance on a variety of track conditions.
	Traxxas Pro ball differential Part #4840

When assembling the Pro ball differential, pay close attention to the direction the bevel washers are facing in the thrust bearing assembly.

Proper orientation of beveled thrust washers

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Lube all diff balls with Traxxas diff grease (supplied with the Pro ball differential). Lube the thrust bearings with Traxxas thrust bearing grease (supplied as well).

After the diff is assembled, start out with a fairly snug tension on the diff adjustment screw. After running the car around the track for a couple of laps, bring the car closer and listen for slippage. When the car accelerates, the diffs should not slip.

The Pro ball diff is very smooth, which allows you to run a slightly tighter setting without sacrificing the smoothness of the diff action. Run the car for a few more laps to allow the diff components to settle. It's now ready to adjust for your track conditions.

Fitting Parts for Smooth Operation

When fitting moving parts together, such as suspension arms, hub carriers, etc, and before you move to the next step, it's a good idea to check the movement of the parts after they're connected to each other. This is very important when it comes to the suspension arms. If any moving parts bind after assembly, then this can -- and will -- cause undesirable and inconsistent performance from the car.

Use a file or a rotary tool to remove any excess material from the parts that are binding. Also, remember that the parts will 'break-in' on their own through the course of running the car, so be careful not to 'over-work' any components. This can also cause premature play and slop, which can hinder consistent handling.

Smooth Out the Steering Linkage

For precise control, the steering linkage needs to move freely. It's ideal that the hollow ball connectors move freely inside of the rod ends. This will allow you to tighten down on the fasteners holding the turnbuckles onto the steering components.

If you are having trouble with a hollow ball not moving freely within a rod end and you are in a crunch for time, try backing off of the fastener just a little to allow it to pivot more freely. Replace the binding rod end and/or hollow ball at your earliest convenience. Also, when threading into in any kind of metal, such aluminum (shown above), I recommend using a drop of medium (blue) compound thread locker on the fastener to keep the hollow ball secure.

The two holes in the bell-crank arm are for adjusting steering sensitivity. In most cases the outside hole will work best, giving you more control over the car (easiest to drive). If you feel that you would benefit from more response, and you don't have that adjustment from your transmitter, mount the rod onto the inside hole. This will give you the feel of a faster servo and the car will respond quickly to your input.

Clean and Lube Bearings

Here's a trick that has been around for a long time, but there are still a lot of racers that have yet to try it. First, you'll need to purchase a bearing cleaning tool and a can of electric motor spray. Before you assemble the car, or if you plan on rebuilding the car, take the time to clean all of the heavy factory grease out of the bearings. This will allow the bearings to spin fast and free.


A bearing cleaning tool, like this one by RPM™, can be found at most hobby shops

Now, apply a few drops of a light bearing oil to the bearing and spin it. This allows the oil to get down into the ball bearings. Doing this to all of your bearings will really free up the car, allowing it to accelerate quicker and reach a greater top speed. Just think of how much smoother the drivetrain will be!

Adjusting the Drivetrain and Tuning with Tires

Welcome to my third and final leg of the Nitro 4-Tec performance series. In this installment, I will discuss ways to get the most out of your drivetrain, and also shed some light on tire choice options for concrete parking lot racing. Correct shift points and properly adjusted differentials are key to fast and consistent laps. These items listed below are the more important areas to concentrate on.

Drivetrain

Two-speed adjustment

Adjusting the two-speed to shift at the correct moment is very important for making fast and consistent lap times. The engine needs to clear out in first gear before shifting into second, but it's not good to let the engine rev-out too high in first gear before shifting. Set the two-speed to shift just as soon as the engine reaches its upper rpm range.

Caution: An early shift point can bog the engine down, resulting in higher temperatures and poor performance. A late shift point can cause excessive wear and strain on the moving parts inside of the engine, and also higher temperatures. Always adjust the two-speed in small increments.

Two-speed adjustments
for gear changes

Two-speed adjustments are necessary when changing the gear ratio in the transmission. Changing the gears on the clutch bell to a higher number of teeth, and/or changing to spur gears with a smaller number of teeth, will result in higher top speeds and take away a little bit of low end punch. This will also cause your two-speed shaft to turn at a higher RPM, thus causing the two-speed to engage sooner.

If you are going to clutch bell gears that have a lower number of teeth and/or spur gears that have a larger number of teeth, then the two-speed will react just the opposite. Turn the adjustment screw clockwise for a later engagement or turn the adjustment screw counter-clockwise for an earlier engagement.

Again, always adjust the two-speed in small increments (1/8 turn), this is a fine adjustment and can get way off quickly if large adjustments are made.

Differentials

Traxxas Pro ball differentials can be adjusted to get the car to react differently in the corners, as mentioned earlier.

A tighter front differential will typically give the car a little bit of a push going into the corners. A tighter rear differential will allow the rear end to come around a little quicker coming out of a corner.

Use small adjustments and try not to adjust both of the differentials at the same time. This could cause the chassis to change too much, worsening your results. On tracks with a high-bite surface, you can run both diffs a little tighter than on a track with less traction.

Larger tracks may also allow you to run both diffs tighter. The car will be under acceleration a lot more on larger tracks, and the tighter diff adjustment will keep the power from unloading as much allowing you to get more power to the ground.

Tuning with Tires

Chassis Handling

Tires are the single most important part of chassis tuning. Without the right tires it may be impossible to get your car to handle well.

It's always a good idea to see what the faster racers at the track are using. Get some ideas from them on what works well in the front and what works well on the rear of the car for that particular track. Start there, and use a good base set-up on your car. Try to get the best performance through tires first before making adjustments to the chassis. When you get to point where the car works consistently well, start fine-tuning the handling with chassis/suspension adjustments.

The stock Nitro 4-Tec tires (left) along with the Pro-Line V-Rage tires (right) are excellent parking lot racing tires where the surface can be bumpy and slightly dusty. On smooth clean tracks that are treated with traction sprays, such as sugar water or VHT, slicks can be used for maximum grip. Check your local hobby shop for a look at all of the different tires designed for track racing.

Compounds

Tire compounds range from very soft to very firm. The softer compounds provide more traction but also wear faster. Keep this in mind when racing in long mains. Temperatures affect compound choices too. Hot temperatures will require harder compounds, and colder weather requires softer compounds.

A good base set-up on the chassis is very important. This can vary from person to person, so the more experience you have with the car, the more you'll learn what set-up is for you... so get out there and practice!

For all of the cool accessories you've seen here on the Nitro 4-Tec in this article, check out the Nitro 4-Tec pages on this website found here: Nitro 4-Tec hop-ups & accessories.

Traxxas offers an incredible list of aftermarket accessories for turning your RTR into a killer racing machine. By practicing the tips in this guide, you'll be sure to make faster, more consistent laps at the track.

I hope everyone enjoyed my Nitro 4-Tec Performance Guide for getting Traxxas' ballistic pavement-pounder dialed in at the racetrack. Remember, the most important aspect of racing is practice. There's nothing better. So, take what you've learned here and go to the track and practice, practice, practice… Happy racing!!!