Jato Performance Guide: Suspension
Jato Performance Guide
The Traxxas Jato is an insane new 2WD nitro stadium truck that is rapidly bringing back the fun in 1/10-scale stadium truck racing. It has a list of features a mile long that includes many items that are not typically found on other stadium trucks in its class.
Jato's suspension system not only offers a wide range of tuning adjustments, but also delivers more bump travel than other trucks. This makes it one very versatile machine for either ripping around on an asphalt parking lot, or blasting the jumps at your local off-road racetrack.
This set-up guide will shed some light on the suspension tuning adjustments, and will point you in the right direction for setting up your Jato for maximum performance.
The stock Jato shocks work great, and withstand plenty of abuse. 1/10-scale stadium trucks are much lighter than monster trucks, and require lighter spring/oil combinations. The composite GTR shocks are very light and extremely durable. The shock bodies are threaded, and there are many different spring options available. They also come standard with friction-reducing X-rings for an excellent seal against dirt and moisture.
These tips will help you maximize the smoothness and performance of the shocks when you rebuild them. The rebuild kit for the stock Jato GTR shocks is available as part #5562.
When installing new X-rings, be sure to lubricate the inside of the X-ring with shock oil before sliding the X-ring onto the shock shaft. The shocks will feel smoother and much more consistent during operation.
Pre-lube the shock bladder
Pre-lubing the shock bladder prevents it from becoming torn or bound up during assembly. Check to make sure the shock bladder is seated correctly into the cap, then spread a little bit of oil around the edge of the shock bladder before threading the cap onto the shock body.
Filling the shocks with oil
The composite GTR shocks share most of the same components with the GTR aluminum shocks from the Revo. The bleed hole molded into the shock cap allows the trapped air inside of the shock body to escape when threading it.
Fill the shock body (close to the top) with desired shock oil. Move the shaft up and down (slightly) to release any air bubbles trapped under the piston (caution: don't move the piston quickly or you could shoot oil out of the shock and into your face.). Thread the cap slowly onto the shock body until the oil starts to seep out of the bleed hole. Tip: Hold the shock at an angle and turn the shock body clockwise into the cap with the bleed hole facing upward. This forces the air bubbles closer to the hole during assembly.
Next, slowly move the piston up halfway into the shock body to release any remaining air bubbles from the shock body. Now, tighten the cap until it's snug. Wipe away the excess oil and it's ready.
The fluid inside the shock body, along with the size and quantity of holes located in the piston, will dictate the resistance of the piston as it moves up and down during the compression and rebound stroke of the shock shaft.
Shock fluid of different viscosities, and pistons made with different hole sizes can be changed to alter the damping performance of the shock.
The GTR shock pistons are 2-hole pistons, which come in two different sizes for the Jato, 1.4mm and 1.3mm. The larger diameter hole allows the shock fluid to pass through more easily, which decreases the damping feel.
The Jato is factory-assembled with the 1.4mm pistons in the front and the 1.3mm pistons in the rear. This is because the front end is much lighter than the rear and does not require as much damping.
This is the same piston setup I use in my Jato for racing, and should be fine for most any track condition that you'll encounter.
Basically, the lighter the oil in the shock, the faster the suspension can react to the bumps on the track surface. Thicker oil will offer more resistance, making it harder for the piston to move back and forth within the shock body. Shock fluids are made from silicone oil, which vary in viscosity.
I recommend stocking shock fluids from 15wt to 50wt for the Jato. This should cover most any situation you'll run into, with the majority of the oils used being between 25wt and 35wt. A good starting point for most tracks is 30wt up front, and 25wt in the back.
Light vs. heavy shock oil
Lighter shock oil will react more quickly to bumps, but will allow more chassis roll in the corners, similar to using softer springs. A shock with oil that is too light for its spring rate will cause the truck to bounce excessively, and will be very difficult to drive.
Heavier shock oil will give the truck more response on smooth tracks, and also prevent the chassis from bottoming out excessively from large jumps. If the oil is too heavy, it will cause the truck to become very unstable on rough surfaces. Try to find a setup that is soft enough to handle the rough sections of the track, but not so soft that the truck is sluggish in the corners.
Weather conditions can also affect the damping performance of the shock oil. Hotter weather typically causes the oil to feel slightly thinner, thus allowing the shock shafts to move a little more quickly. If the temperature outside is considerably hotter than the last time you ran, you may need to run a slightly thicker oil in your shocks to get them to work the same as they did before.
There are eight different spring rates for the Jato. For off-road racing, the Jato tends to work a little better with the softer spring sets.
I generally use the orange (#5428) springs up front and the tan (#5429) springs in the rear.
Soft springs are more beneficial on slick and bumpy tracks and allow a little more chassis roll in the corners, which improves traction and bump handling. They also give you a little more time to correct the chassis when it gets out of shape from driving over rough sections of a track.
Firm springs are more sensitive to input. A track with large, high-speed jumps may require a firmer spring to help keep the chassis from slapping the ground too hard, which can upset the handling of the truck. Keep in mind that when you change to a firmer spring, you may need to go to a thicker shock oil to keep the shock from rebounding too fast.
An important thing to remember when reducing or adding weight to the chassis is that you may need to adjust the spring rate or firmness to compensate for the weight change. The stock springs were selected with the stock weight of the truck in mind.
If you intend to remove the EZ-Start® system and replace some of the heavier steel parts with aluminum ones, you may want to try dropping the spring rate a notch or two to maintain the same suspension performance.
The length of the GTR shocks is adjusted on the Jato by threading the shock end up or down on the shock shaft. This is just a fine-tuning option and should not be used to make large changes. I do not recommend lengthening the shock more than a couple of millimeters. If the shock end is threaded off of the shaft any more than this, it is in danger of pulling completely off of the shaft under rough conditions.
I use this adjustment when I want to get just a little more down travel, but I don't want to change the shocks' position, which will change the damping and spring force at the wheel.
The base setting for shock length is 96mm (end to end), which allows for a safe adjustment to 98mm.
There are four mounting positions on the lower front and rear suspension arms on the Jato. The inside holes are less progressive, and allow a little more chassis role in the corners.
The outside holes make the suspension more progressive as it is compressed. This will give the truck a slightly firmer feel.
Keep in mind that changing the lower position of the shocks will also alter the down travel of the arms (see down travel below) and the ride height of the chassis, so you may need to make other changes if you want to keep those current settings.
There are three upper shock mount positions. Changing the upper mounting positions to the outside holes will add a firmer spring rate feel to the wheels, but will speed up the damping (faster compression and rebound). I normally mount the shocks in the middle (B) location on the shock towers and start with the #2 position (2nd from inside) on the arms for most tracks. This gives me a good amount of suspension travel for most rough tracks, which makes the truck easier to drive.
Ride height is adjusted by threading the preload collars on the shocks up or down on the shock body. Do not use the length of the shock to determine the ride height. This will make a very twitchy and unpredictable truck.
I also do not recommend using extra preload to give the shocks a firmer feel. If you want to firm up the suspension, use a firmer spring. You should only use the pre-load adjustment for adjusting ride height.
Generally, it is best to run the chassis as low as you can, but still high enough to negotiate the bumps and jumps on the track. Smooth surfaces will allow lower ride height settings, and bumpy tracks will need a higher stance. Ride height is checked with the truck on a smooth flat surface. Push down on the front and rear of the truck at the same time and allow the shocks to rebound the truck to its set ride height.
Camber is the angle of the wheels in relation to the surface when looking at the front or rear of the truck when the truck is set at ride height. Negative camber is when the top of the wheels point toward the inside of the chassis. Positive camber is when the tops of the wheels point outward. If they are standing straight up, it is set at 0-degrees camber.
Camber can easily be measured by using a simple, inexpensive camber gauge. Most hobby shops carry camber gauges for less than $10. Check with your local hobby shop for price and availability.
The default camber setting from the factory is -1.0-degrees, front and rear. A good base starting point for most racing conditions is -0.5-degrees in the front, and -1.5-degrees in the rear.
Typically, more negative camber equals more traction. If you are looking for a little more bite in the front or the rear of the Jato, just dial in a little more negative camber. Be careful not to go too far. There is a window of adjustment from 0 degrees to about 3 degrees of camber. Going further than that will decrease the contact patch, traction will be lost in the corners, and handling will suffer.
Camber gain is the progressive change in the camber angle as the wheel moves up during the compression stroke of the suspension. Typically, the negative camber angle will increase as this happens. This provides a little more side bite as the suspension is compressed. You can alter the rate of the angle change by adjusting the length of the camber link and selecting different mounting holes.
Lengthening the link will reduce camber gain, which will help with stability and traction. Shortening the link will reduce traction, but will provide a little better bump handling.
The base setup for camber link position in the front is to have the link attached to the inner hole on the caster block and the other end attached to the inner hole on the bulkhead. If you want more steering, move the outer link to the outer hole. For less steering, try the outer hole on the bulkhead.
The rear is adjusted by moving the camber link horizontally between the different mounting positions on the bulkhead. The inner most positions will improve rear bite, and the outer positions will improve steering.
Caster is the angle of the axis that the front hub carriers pivot on when looking at the chassis from the side. More positive caster will allow the wheels to lie back a little more when they are turned one way or the other. Typically, a larger caster angle will provide more steering coming out of the corners.
Caster is adjusted by changing out the caster blocks and the steering blocks. There are two caster block sets available for the Jato, 30-degrees (stock) and 25-degrees.
30-degree blocks are good to start with, but if you feel you need a little less steering, try the 25-degree set.
Toe angle is the angle of the front and rear wheels when looking at the truck from above. If the front of the wheels point inward, this is called "toe-in," and if they point outward, it is called "toe-out."
The front wheels are normally set with 0 degrees (straight) of toe. Toe-out will give the truck more instant steering. Toe-in will make the truck feel a little more stable with less response. The window of adjustment is from 1.0-degree of toe-in to 1.0-degree of toe-out. I generally run 0-toe angle up front, and if the truck starts to feel a little loose, I'll add a little toe-in to calm it down.
Rear toe angle is a very important setting. This is nearly as important as selecting the right tire. Increased rear toe-in will make the truck more stable and will give the truck more rear bite. This will also reduce steering some, but the Jato turns so well, overall steering is really not affected. However, keep in mind the steering response will be reduced slightly from the increased rear toe angle.
There are three rear toe plates available for the Jato: 3-degrees, 4-degrees (stock part# 5558), and 5-degrees. The 3 and 5-degrees plates are both included under the part# 5557.
I normally run the 5-deg for most conditions, but if you are experiencing too much rear bite, try the 4-deg plate.
Anti-squat refers to the resistance of chassis to squat under acceleration. The level of resistance depends on the angle of the lower inboard suspension pins that the rear suspension arms pivot on.
The angle can be changed by swapping out the lower suspension pin mounts. There are four anti-squat blocks available: 1.5-deg, 2.25-deg (stock), 3.0-deg, and 3.75-deg. All of these blocks are included in part# 5559.
Increasing the anti-squat angle will reduce the tendency of the rear end to squat under acceleration. This provides a little more forward bite, but at the expense of side bite and bump handling.
I like the 1.5-deg block for its handling over rough terrain and its excellent side bite when accelerating out of the corners.
Note: Refer to the Jato manual (pg.# 42) for the installation procedure for the anti-squat blocks.
The most important thing to remember is that the left and right shocks need to be the same length. See "Shock length & position" above.
Measuring down stop
Smooth high bite tracks will allow you to take advantage of less down travel. Less down travel will make the truck more responsive when cornering, and enable the truck to react more quickly to steering input.
More down travel will handle larger bumps and jumps much better, and will be a little easier to drive overall. A good base starting point for down travel is approximately 32mm in the front and 30mm in the rear.
Down stop limiters
Traxxas also offers down travel limiters (suspension down stop screws #5554) that are easily installed into the suspension arms of the Jato to adjust how much down travel is allowed. I rarely use these screws in off-road racing, since most of the tracks I race on are pretty rough. However, when racing on very smooth and high-bite tracks, limiting the downtravel helps keep the Jato planted to the surface.
The roll center adjustment on the Jato changes the geometry of the camber in relation to the lower suspension arm. The affects of roll center work a lot like a sway bar, but it is built into the geometry of the suspension system.
The inner camber link can be adjusted up or down to raise or lower the roll center of the chassis. By raising the roll center (lowering the inner end of the camber link), you increase your chassis roll stiffness, which is essentially the resistance of the chassis to roll (sway) in a corner.
The inner camber link can be shimmed up or down with spacers to adjust roll center. Mounting the link directly to the bulkhead is the lowest position, and will reduce steering, but it will also increase steering sensitivity, and may make the Jato a little more difficult to drive. Raising this position will lower the roll center, and allow the truck to rotate more in the corner. This will also make the truck a little more forgiving to drive.
I like to start with the lowest position in the front, since the Jato already steers so well. This also helps keep the front end from dipping while entering a corner. I'll raise this position if the track becomes badly rutted or pitted in the corners.
With most nitro tracks being outdoors where they tend to get hard-packed and dry, the traction is usually at a minimum. So, I'll start off with a setting that will give me the most rear bite as possible. I use the #3 position on the bulkhead, which is the inner most position on the upper row.
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