Maxx-imum SportMaxx Part II
In part one of my Maxximum SportMaxx series I mentioned hop-ups that are available to improve the performance, durability, and consistency of the S-Maxx. Not all of those items were used for function. Of course, some were chosen just because they look very cool on the truck, and did not add any excess weight or drag to the chassis. Not all of the items that I had listed before are absolutely necessary either, but each one of them does provide a particular benefit that can be useful in achieving faster and more consistent lap times. You may have also noticed that I did not list every aftermarket hop-up item that is available for the S-Maxx. In effort to keep the weight of the truck very low, I limited the amount of aluminum components on the truck. Although aluminum is stiffer and stronger than the stock plastic parts, I decided to keep the bulkheads and suspension components plastic for this particular project.
The factory S-Maxx suspension is highly adjustable and performs as well as any other suspension system that I\'ve seen. Not to mention, seeing the stock chassis/suspension components survive some the most vicious thrashings that I\'ve ever put an R/C vehicle through leads me to believe that I shouldn\'t worry so much about the durability of the stock plastic components. This is especially true when considering that this truck is going to be extremely light, and used for racing rather than bashing.
|Setting up the S-Maxx is a lot like setting up a nitro stadium truck because it is 2WD, but things like shock oil, springs and other general suspension settings will need to be different due to its larger size and weight compared to a typical 1/10-scale nitro stadium truck.|
This, combined with my experience gained from racing the T-Maxx over the past three years, have allowed me to find a very good 3base2 set-up for this 2WD Maxx machine. A good base set-up is what I try to find on all of my cars and trucks, because going to different tracks without one can really create a lot of extra work for you on race day. Starting with a good all-around set-up frees you up for other important things like spending quality 3wheel-time2 on the drivers stand practicing lines and jump sequences, making sure that all of your batteries are topped off, and organizing all of your tools and pit accessories for the day\'s racing at the track. Follow closely for some pointers in this segment that will improve the handling of your truck and get you closer to that magic set-up.
Four shocks or all eight?
Over the past few years racing the T-Maxx, I\'ve tested various shock arrangements and suspension set-ups. I\'ve used the 8-shock set-up with many different spring and oil combos. I\'ve also used the 4-shock set-up with firmer springs and thicker fluids. I\'ve even tried eight dampers with four springs, along with various viscosities of fluid in them as well. With the 4-shock set-up, it was a little difficult to find the right combo of springs and oil to provide that 3sweetspot2 setting for the T-Maxx. This is due to the extra weight of a the 4WD truck. For vehicles over 7lbs., there is just simply not enough total volume in a 4-shock (1/10-scale size shock) set-up to handle the load consistently on today\'s nitro off-road tracks. Using four 1/8-scale buggy (larger volume) shocks is an alternative that does work well for the T-Maxx, however 1/8-scale shocks are heavier and in most cases more expensive, so going this route really isn\'t gaining much for you. I\'ll speak more on this subject in a future article when I focus on the T-Maxx.
This is where the Maxximum S-Maxx is different. The S-Maxx that I have created for this segment is under 7lbs. That means that it is over a pound lighter than a stock S-Maxx and over 2 ? lbs. lighter than a stock T-Maxx. Although the 8-shock set-up works great and can be tuned to handle any kind of track condition, the lighter weight 4-shock set-up will work just fine on this sub-7lb. racing S-Maxx chassis.
When going to a 4-shock set-up, the remaining four shocks will be now supporting the whole truck, so it will be necessary to go with firmer springs. For a 7lb. off-road vehicle a medium/firm to firm 1/8-scale buggy spring works great. There are many different brands of springs out there. I chose a set of Ofna 1/8-scale white (firm) front springs for all four shocks on my test truck. 1/8-scale buggy rear springs can be used as well, but they are too long and will need to be trimmed before they are installed onto the shocks. I recommend using front springs.
When setting up an off-road vehicle you want the shocks to react quickly to the little stuff, but you don\'t want them to be too fast, which will cause the truck to feel bouncy and bottom out heavily when landing from larger jumps. When choosing shock oil, try to go as light as you can while still providing enough damping for the big jumps.
I feel that the 2-hole pistons that come in the Traxxas Big Bore shocks work the best for most off-road track conditions. When only using four shocks on a 7lb. S-Maxx, the standard 30wt to 50wt oils that you would normally use in an 8-shock set-up will be too light. For a 4-shock set-up, keep your shock fluids in the 60wt to 80wt range. Keep in mind that this is with a 2-hole piston set-up. Your current climate will also be a factor in choosing the best shock oil. The relative temperatures during my test sessions were in the upper 80\'s to lower 90\'s. Cooler temperatures may require lighter oils.
Here\'s the shock set-up on my S-Maxx. Note that this set-up is for most track conditions with an ambient temperature of around 80 to 90 degrees.
Front Shock Set-up
Damper: Traxxas Big Bore w/ Ti. Nitride shock shafts
Oil: Team Associated 80wt
Spring: Ofna 1/8-scale buggy front white (firm)
Travel Limit: no limiters
Length: 110mm (top of cap to bottom of rod end)
Location: Upper - A (middle) Lower - #3 (3rd from inside)
Rear Shock Set-up
Damper: Traxxas Big Bore w/ Ti. Nitride shock shafts
Oil: Team Associated 80wt
Spring: Ofna 1/8-scale buggy front white (firm)
Travel Limit: no limiters
Length: 110mm (top of cap to bottom of rod end)
Location: Upper - A (middle) Lower - #3 (3rd from inside)
Ride height is adjusted by adding or taking away spring pre-load spacers. Do not use the length of the shock to set ride height. This will make a very twitchy and unpredictable truck. The suspension needs down travel for stability. Also, do not use extra pre-load spacers to give the shock a firmer feel. If you want to firm up the suspension, then 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, but still be 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 flat smooth 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. A good starting point is when the truck rebounds to where the front and rear suspension arms are level (parallel with the ground). You can run the rear a little higher than the front for more steering into the corners.
Down travel / Shock length
Down travel (also known as droop) is the distance that the suspension arms travel downward as you lift the chassis from the surface. This is determined from the point at which the truck is at its set ride height.
The length of the shocks, along with the shock mount position, will dictate how much down travel the suspension arms will have. The most important thing to remember is that the left and right shocks need to be the same length. You can decrease the length of the shocks by placing 3mm I.D. spacers underneath the pistons in the shocks. I\'m not using in spacers in our test vehicle. The larger the spacer the shorter the shock will be. Rough tracks or tracks with large high speed jumps will require more down travel. Smooth high bite tracks will allow you to take advantage of less down travel. This will make the truck more responsive through the turns.
The base length and position of the shocks for the S-Maxx are listed above under Shock set-up.
Camber is the angle of the front and rear tires in relation to the surface as seen from the front or rear of the chassis. If the upper end of the wheel is leaning inward toward the chassis, then this is known as a Negative camber setting. A slight amount of negative camber is most widely used by racers so that when the a vehicle leans into a corner the outside tire\'s contact patch will 3square-up2 with the racing surface providing more traction. Do not go too far though, as this will start to decrease the tire\'s contact patch with the surface, and traction will be lost; Start with 1 to 2 degrees of negative camber.
Positive camber is never used. In most cases, positive camber will cause the sidewall of the tire to roll under the wheel when cornering causing inconsistent traction through the turn.
Caster is the angle at which the axles and hub carriers turn on. The S-Maxx and the T-Maxx both have adjustable caster up front. Adjusting this setting is accomplished by moving the plastic spacer clips around on the upper suspension pin, altering the location of the upper arm from front to rear. The further back that the arms are positioned, the more the caster increases, and the more 3on-throttle2 steering you will experience. My S-Maxx is configured for 7? of caster (see illustration).
Toe angle is the angle that the front and rear wheels are positioned at when looking at the vehicle from above. An easy reference is to think of it as looking down at your feet. If your toes were pointing outward, then you would call that "toe-out2. If your toes were pointing inward toward each other, then you would call that 3toe-in2.
Front toe angle will determine your 3instant2 steering response. Toe-in will reduce response, and toe-out will quicken the response of your steering. Toe-out will also give you the feel that your truck has more steering through the corner.
Rear toe angle is a very important setting, especially on a 2WD vehicle. This, next to the tires, is the main factor that dictates how much traction and control you have over the vehicle on and off throttle. More toe-in dialed into the rear will make the truck more stable and will give the truck more rear traction. Do not go too far with this though, as you will lose steering and response, forcing you to over-work the truck in the turns to hold a tight line. Toe-out in the rear will basically render your truck undrivable with over-steer. Toe-out should never be used.
As with any 2WD vehicle, obtaining rear traction on a slick surface is usually pretty difficult. Adjust these settings to get as much rear bite as possible, but be careful not to go too far.
This is my base set-up for wheel angles:
Camber Caster Toe Angle
Front: -1.5 ? Front: 7? (mid) Front: +0.5 ? (toe-out)
Rear: -2.0 ? Rear: +2.5 ? (toe-in)
Maxx-imum Sportmaxx Part III - "Chassis"
75cc Fuel Tank
The first modification that I made to the chassis was the installation of the Traxxas 75cc fuel tank, part #4448. This is the same tank that is found on the N. 4-Tec and the N. Rustler models. The stock 125cc fuel tank works fine, and offers well over 10 minutes of run time. It\'s a perfect tank for bashing or racing on a sport level.
When it comes down to getting everything that you can out of your small-block truck for serious racing, I recommend using a lower profile and/or smaller capacity fuel tank for several reasons:
1. The TRX 2.5 Racing Engine, as powerful as it is, does not consume a large amount of fuel very quickly. Even in race conditions, you can expect over 6 to 7 minutes of run time from a 75cc tank (with a properly tuned engine of course). The extra fuel and weight of a 125cc tank really isn\'t needed, when most racers pit around the 5-minute mark anyway.
2. Like I mentioned above, the tank is smaller, lighter, and lower to the chassis for improved weight transfer in the corners. This tank is very low-profile and positioned out of harm\'s way, which means it is very unlikely that you will damage the tank in the event you crash or roll over in a turn.
3. Due to the high profile, and large capacity of the stock 125cc tank, the mixture changes that the engine will go through from a full tank to an empty tank can sometimes cause tuning difficulty when trying to find that perfect needle setting for a race. With the stock tank, it is typical to have to tune your engine to be a little bit sluggish when the tank is full, so that it will not be too lean when it gets to the bottom of the tank. This will leave your truck under-powered for the first few laps of a race, and it is just not feasable to have to make an extra pit-stop just to retune the hi-spd needle. When racing, you want to be able to run an optimized needle setting for maximum performance for the duration of the entire tank. A smaller tank gives you that ability without carrying the extra weight.
5-Cell Receiver Pack
The next mod is the installation of a 5-cell NiMH flat reciever pack to power the electronics. A 5-cell/6volt receiver pack is the only way to go when getting the most out of your radio equiment. Rechargable 5-cell receiver packs offer more power to your servos to deliver quicker steering response and more powerful braking. For this project, I am using a 5-cell flat style pack. Check with your local hobby dealer for the correct receiver pack.
The receiver pack is mounted under the chassis for low CG, and is also strapped to the chassis with with two Zip ties. The Zip ties are plenty strong enough to hold the pack securely without the need for mounting brackets or extra hardware. Notice the clearance between the bottom side of the battery pack and the lower edge of the tranny skid plate in the photo above (see arrow). The battery pack must not extend below the tranny skid plate, or the battery pack can become damaged when landing on top of another jump or truck. This is why I do not recommend hump style packs for this application.
75cc Fuel tank/5-cell receiver pack installation instructions
Note that these instructions are for the aftermarket Traxxas 4922X hop-up chassis. The measurements will be different for the stock chassis.
The 75cc tank will be located to the driver\'s side of the transmission, and will be mounted using the three mounting bosses located on the bottom of the tank.
Routing of fuel & pressure lines
Mount and secure the fuel line to the chassis with small Zip ties. Use the existing (stock) fuel tank mount holes for the small Zip ties. Tip: Coil up some extra fuel tubing in a circle before connecting to the carburetor. Since the fuel pick-up is at the bottom of the fuel tank, your engine will only run off of what fuel is in the fuel line, in the event that your truck has flipped over onto its top. This extra fuel line will help ensure that you have enough fuel for your engine to run on while waiting for a turn marshal to flip your truck back over.
Remember: Never gas the throttle when upside down waiting for a marshal. First of all, if your engine is tuned correctly, it will run just fine upside down. Secondly, the more you throttle it, the faster the engine will consume the fuel in the line, inceasing the chance of your engine stalling out before you get back onto your wheels. Plus, this is also dangerous for the marshal who is being so kind enough to put your truck back onto its wheels.
Route the pressure line across the top of the transmission over to the exhaust pipe. Tip: Use a body clip (left) to hold the tubing close to the tranny case to keep the line from getting caught in the spur gear.
Trim skid plates
You won\'t save a lot of weight by trimming your skid plates, but you may save them from snapping completely off. If the truck lands just right on its front or rear end, it can snap the skid plates at the bend. Shortening them will improve their durability while still maintainng the function that they were designed for.
Note that the front skid will need more kick-up than the rear. Trim the rear just past the bend. The front needs to be longer to prevent the front end from digging into the track when landing nose-down from a jump.
Direct mount steering servo
As I mentioned in the first installment, I chose to mount the the steering servo directly to the chassis using four 3x8 machine screws (w/ washers) and four 3.0mm lock nuts.
Ball bearings in steering bell cranks
The steering bell cranks on the Maxx trucks pivot on plastic bushings. These bushings can be replaced with 5x8 ball bearings for smoother operation. Traxxas part #2728 includes two (2) 5x8x2.5 ball bearings. The bell crank system requires four (4) total ball bearings.
Aluminum transmission skid plate
The Traxxas aluminum transmission skidplate (part #4947x) for the Maxx trucks is designed to brace the lower chassis braces and to protect the tranny case from damage. Once bolted on, this component is very instrumental in improving the lateral strength of the entire chassis.
Keep your receiver box
Although this is not a hi-performance hop-up or a super-trick modification, there really isn\'t another chassis component more important on a nitro off-road vehicle than the receiver box. If it wasn\'t for this little plastic container bolted onto your rig, your receiver would be very vulnerable to every element known to exist at a track i.e., dust, water, mud, fuel, etc. Any one of these can contaminate your precious radio receiver, not only causing you to fall out of a race, but it could also cause your truck to fly off of the track and head toward the nearest wall, highway, pond, or even worse, another person - causing severe damage and a possible injury to a spectator. It\'s always best to keep your receiver protected. Besides, it\'s a great place for some more cool stickers, heh heh heh....
Maxx-imum SportMaxx part IV
On high bite tracks that offer a lot of grip, a properly adjusted slipper can help prevent the front end from lifting up when accelerating out of a corner. This will keep the front end down preventing a push or under-steer.
On slick tracks or surfaces that do not offer much traction, the slipper can be loosened enough to limit wheel spin to keep the rear end stable under acceleration.
A good starting point for the slipper setting on the S-Maxx is to tighten the slipper nut all the way until the spring is stacked solid, then back the nut out 1/2 turn. Experiment with different settings for your track conditions to obtain optimum traction with as little wheel spin as possible. Be careful not to run the slipper too loose. This will cause excessive heat build-up and could result in a melted spur gear.
It is fairly common for people to wonder why their spur gear wobbles when they rotate the gear after assembly. This is because the spur gear rides on friction pegs, and the gear itself is not designed to come in direct contact with the pressure plates. It basically free-floats on the pegs and since there is a little bit of room between the gear and the pressure plates, the gear can sometimes appear crooked or warped when it actually isn\'t.
Once the engine is warmed up and has revved out a few times, the spur gear should straighten up. If the gear seems to be too far out of whack, then apply an even amount of pressure to one side of the gear with your fingers to straighten the gear out before your start the engine. I have never seen any damage occur to a spur gear due to this situation, but this tip may make a lot of people feel a little better about it before they run their truck.
Shaving the front axles
Removing the un-used material from the front axles isn\'t much of a speed secret, but it is definitely a cleaner look for the front of the the S-Maxx. Unless you just want to use them as spares for your T-Maxx, the universal ears on the axles are not used for anything. You won\'t need them for the 4WD conversion kit either, because the 4WD kit comes with its own pair of axles.
Clean the bearings
Cleaning the ball bearings inside your Maxx is a very simple task, yet very effective in improving the performance of the truck. There are different brands of bearing cleaning devices out there, but they all perform the same function; getting the dirt and grime out of your bearings. Your local hobby shop should carry at least one or two types of these inexpensive bearing cleaning tools. The model above is the Bearing Blaster by RPM.
Here\'s a speed tip for new models: Cleaning the heavy factory grease out of the model\'s ball bearings and replacing it with a light and thin bearing oil will decrease the drag within your truck\'s drivetrain considerably. This will not only increase the speed and power of your Maxx truck, but it will also allow the engine and clutch assembly to run cooler and much more efficiently.
Locate the bearing onto the conical adapter inside the tool, then cover with the top. Insert the bearing cleaner straw into the cover, and flush out the bearing. Electric motor spray works very well for cleaning bearings. Caution: Always wear eye protection when using pressurized cleaning solvents. Repeat this step until the bearing spins very freely and all of the gritty feeling of dirt has completely gone away. Once the cleaner has dried away, lubricate the bearings with a thin bearing oil. It may take a while to do your whole vehicle, but is well worth it in the end.
When cleaning sealed bearings, the rubber seal must be removed from the bearing for easier cleaning. After the bearing is clean and relubricated, simply press the seal back into the bearing until it snaps in.
Mounting the TRX2.5 throttle bell crank onto the Traxxas 4922X chassis
There will need to be a few holes drilled into the Traxxas 4922X hop-up chassis to mount the throttle bell crank post for the slide carb on the TRX 2.5 engine. Use the template on the instructions at this link to mark the locations for the holes that need to be drilled.
Once complete, the assembly should look like this on the bottom of the chassis.
Make sure that when the carb is in its set idle postion, the linkage looks like this. Notice how the throttle servo horn and the throttle bell crank are aligned with each other nearly perpendicular to the rods. Also, make sure that when the carb is at idle, the brake is not engaged; meaning that there is no pressure being applied by the brake arm to the brake calipers.
When the transmitter trigger is at neutral and the carb is at idle, there should be a small gap between the set screw collar and the linkage eyelet on the servo horn. This will ensure that there is enough pressure against the throttle arm to keep the slide valve closed in the idle position.
Throttle bell crank bearings
Smooth out the action of the throttle linkage by installing two 5x8 ball bearings (Traxxas part #2728) into the throttle bell crank.
Replace brake tubing with coil spring
I use this mod on all of my vehicles. A spring provides a much more linear feel for your brakes vs. a piece of fuel tubing. With fuel tubing, there is a very fine line between delivering a comfortable amount of progressive pressure against the brake arm and instantly locking up the brakes. A coil spring delivers a more predictable amount of pressure against the brake arm when entering a corner. This benefit is especially valuable on 2WD vehicles.
I\'ve tested different coil springs over the years from various mechanisms and gadgets. I have found that the coil spring from a servo saver works very well for this application. You can experiment with different lengths to get the desired progression and feel. The brake spring on my S-Maxx was pulled from a stock Traxxas S-Maxx/T-Maxx servo saver, and cut down to 16mm in length.
See you at the races
There you go; everything you need to know to build a super-lightweight, and very competitive 2WD monster Maxx race truck. I know that there is quite a lot to digest here, so try performing one mod or two at a time and see where it takes you. This will better allow you to understand what each mod was designed for.
The S-Maxx in this article weighs in at a very respectable 6.9lbs. Compared to the stock S-Maxx (8.2lbs.), the Maxximum S-Maxx is over a pound lighter without sacrificing durability. In fact, this S-Maxx is not only considerably lighter, but it is also more durable and consistent than the stock S-Maxx. This Hi-performance S-Maxx is a blast to drive on the track and runs right with the best 1/10-scale stadium trucks out there.
The tips and mods that I have discussed here are mainly geared toward racing, but what works well on the track also works great for bashing around too. So, even if you don\'t race, try some of them out, and see what they can do for you. For you race-junkies, hopefully there are some ideas in this guide that will help shed some unwanted seconds off your laptimes.
If you\'ve been wondering where all of the cool flame decals on my chassis came from, pick up the Traxxas accessory flame decal sheet (part# 3913X). The graphics on this decal sheet are very sweet, and compliment the chassis quite nicely giving the truck a custom look when the body is off. So, good luck with your new Maxximum S-Maxx, and for all of you 4WD guys and gals out there, stay tuned for some serious T-Maxx talk coming soon where I\'ll explain the ins and outs of racing the most popular truck on the planet. Until next time, take care and happy racing! See ya.....
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