The steering system on a full-size off-road vehicle takes a lot of abuse. It is the same with RC. Whether you’re driving fast over bumps and jumps with an Yeti or crawling over rocks with an SCX10 II or doing a little of both with a Wraith, the steering is constantly taking hits. Whatever you hit, roll over or dig up onto, usually contacts the steering system first. In a similar fashion, and again just as it is in full-size off-road, one of the best ways to improve the capabilities of your RC vehicle is to make improvements its steering system. Instead of installing a hydraulic assist, in RC, we upgrade the servo. Instead of installing a custom pitman arm, in RC, we use an aluminum servo horn. These upgrades are simple tasks that can be performed by hobbyists of any experience level (if you aren’t an adult, get adult assistance and/or supervision).
Installing a New Servo Horn
STEP 1. Depending on your model, it may be necessary to remove some components to make servo access easier. On this SCX10, the bumper and cross-member have been removed.
STEP 2. Remove the servo horn. The horn is most likely retained by a Phillips head screw, or a 2 mm screw. Either way, the screw is easy to access and remove. There may be a lock washer under the screw, so be careful not to lose it. Set this hardware aside. A small dish or tray is handy to prevent losing parts. Pull the servo horn off the servo.
STEP 4. Select your new servo horn. Axial offers heavy aluminum servo horns that are essentially indestructible. These horns are offered in 23, 24 and 25 spline counts to fit any brand of servo. Axial servos use 25 spline count output shafts. These servo horns are highly recommended and go a long way towards improving a vehicle’s reliability. They should, however, only be used with heavy-duty metal gear servos that can withstand the forces that will be pass through the steering to the servo.
STEP 5. Attach the steering link to the servo horn. This is pretty simple. Note that even if you use a servo horn with threaded holes, you still need a locknut on the screw that attaches the link to the horn.
STEP 6. The vehicle must be powered up to properly install a new servo horn. Install a battery and turn on your transmitter. Plug in the battery and turn your vehicle on. Next, set your transmitter’s steering trim (channel 1) to zero. If your transmitter has sub trim, you need to also set that to zero for steering. After the trims have been set to zero, you can turn off the vehicle and then the transmitter.
STEP 7. Slide the servo horn onto the output shaft and secure it with the main center screw. Axial’s HD servo horns are a double clamping design, so if you’re using one, you will also need to tighten the two 1.5 mm screws on the sides of the horn. Tighten all three screws down tight. Thread lock is not recommended on any of these screws. If you find, over time, that the main screw repeatable loosens and using a new screw doesn’t help, you can use a small amount of medium strength thread lock. Never use high strength thread lock.
Removing an Old Servo
Refer to Steps 1 & 2 above to remove the servo horn from the installed servo.
STEP 3. Open the radio box using a 2 mm wrench (it may vary by model). With the lid removed, you will be able to carefully unplug the servo lead from the receiver. Again, be careful so that you do not damage the receiver and its internal circuit board. The servo lead (wires connecting it to the receiver) may be attached to the chassis in some places with cable ties. It is essential that you be extremely careful when cutting any cable ties as you could easily damage the small wires.
STEP 4. Before removing the servo, take note as to which side the output shaft sits. The servo itself is retained by four screws. These may be Phillips or hex. Some screws may have built-in wide shoulders and others may have washers. Either way, carefully put this hardware aside. The servo can now be removed and set aside.
STEP 5. Place the new servo on its mounting plate. Servos can vary in size, but Axial vehicles have adjustable servo mounts. If you do need to adjust the servo mount (one is in a fixed position and one adjusts), the process is the same on SCX10 and Wraith, which all feature servos mounted directly on the front axle. On these vehicles, with the new servo set aside, remove the mounting plate from the axial. You can make this process easier by disconnecting the upper links and the upper shock mounts. This will allow the axle assembly to pivot forward and give you much better access to the screws attaching the servo mounting plate to the axle. After you remove the servo mounting plate, turn it over and locate the screw securing the adjustable mount. To identify this mount, look for the screw going into an oval shaped hole. The oval shape is what allows for the side-to-side adjustment for narrow or wide servos. Now, simply loosen the screw a small amount (usually a partial turn is all that’s needed) and test fit your new servo. Holding the servo in place, tighten the screw back down. Remove the servo and reinstall the servo mounting plate to the axle. You can now reconnect the upper links and shocks. If the male and female driveshaft pieces pulled apart, make sure it gets reconnected as well (before reconnecting the upper links).
STEP 6. Slide the new servo into the mount, paying close attention to which side the output shaft sits. When working on an SCX10 or Wraith, and when viewed from the front, the output shaft is on the right-hand side. Secure the servo with the four screws that were holding the original servo in place. If the screw holes are stripped out and the screws cannot be fully tightened, you will need to replace the plastic servo mounts.
STEP 7. The next step is routing the servo lead back to the radio box and receiver. Make sure the wires are not near any moving parts such as articulating suspension components or driveshafts. This is especially true if your Axial model has exposed gears. Small cable ties can be used to keep wires secure and out of harm’s way. Note that Axial includes provisions to secure wires on vehicles such as the SCX10 and SCX10 II. These should definitely be used to secure wiring.
Excessive wire should be neatly stored in the radio box. Do not make the wires too tight or they will get damaged as the suspension articulates. The wires should be slack enough to allow for complete suspension movement.
Once the wiring is complete, you reinstall the radio box lid. Some radio boxes are not fully sealed, but if you are using a sealed box, you should add grease to the area where the wires pass into the box.
STEP 7. Finally reinstall the servo horn on the centered servo. Refer to STEP 7 above. Your servo swap is complete! You can now power up your radio and vehicle and go out for a drive.
TIP: Radio Settings
You may need to slightly adjust your steering trim to get the vehicle to track straight with no input. If your transmitter has sub trim, this adjustment is used first.
If your transmitter has end-point adjustments, you should also use these to adjust how far the servo travels in either direction. A servo that turns farther than the steering system will allow can eventually burn out. The best tool to see if your servo is moving too far and straining is your ear. All servos, especially digital models, make an audible whine when pushing against a resistance. Bench test your steering. If you hear a whine at full lock in either direction, adjust the end points until you don’t hear a whine. If your transmitter doesn’t have end point adjustments, it may have dual rates, which also reduces steering throw, but does both sides simultaneously.
Axial’s Ready-to-Run (RTR) vehicles are true hobby-grade products and, as such, they use sophisticated electronic components. One of the primary advantages to such high-tech gear is adjustability and an area of adjustability includes battery type. Axial’s electronic speed controls (ESCs) are designed to be used with a variety of battery chemistry types and can, and should, be adjusted for the type of battery you’re using.
IMPORTANT NOTE: As a safety measure, Axial uses the LiPo setting as the default setting on the ESC, but NiMH batteries, are often recommended for use with RTRs. NiMH batteries will provide best performance when the ESC is used in NiMH mode.
LiPo batteries must be run with the ESC set in LiPo for safe use. This isn’t optional. When properly set in LiPo mode, Axial ESCs are designed to eliminate the chance of over discharging the battery and permanently damaging it, which is a potential safety issue. As such, LiPo batteries should never be used in any other mode other than LiPo mode on the ESC.
NiMH batteries will work in LiPo mode, but there will be a noticeable reduction in performance that will suddenly become apparent as the pack starts to lose voltage (discharge). This is because LiPo mode has what is called LiPo cutoff or low voltage cutoff. As the voltage drops in the NiMH pack, it is still delivering usable power, but the LiPo cutoff engages and impairs performance. The LiPo cutoff is designed to reduce power to the motor in order to keep the battery at a safe minimum voltage. Let’s go over setting up NiMh mode on the various Axial ESC offerings so you can get maximum performance when using this type of battery.
AE-2. The AE-2 is a brushed motor speed control. While Castle Creation’s Castle Link system can be used to link the ESC up to a computer (availabe as an aftermarket item,) for ease of use, the AE-2 can be programmed manually by using the throttle trigger on your transmitter to indicate yes or or no to selections as you scroll through each option. To get the best performance when using a NiMH, the ESC should be programmed to operate in NiMH mode.
When programming, as a safety measure, remove the pinion from the motor. This will prevent the gears and/or vehicle from moving and causing damage to the vehicle or you. Turn the transmitter on and then connect a freshly charged battery to the ESC. Hold full throttle and turn on the ESC. You will hear four tones from the ESC and then another four tones. After the second series of four tones, release the throttle. The ESC will beep twice indicating you’re in programming mode.
There are three settings that can be adjusted on the AE-3. Each setting, in turn, has a varying number of options. You will use your transmitter’s throttle to select yes (full throttle) or no (full brake) for each option. When you select yes, the next setting will come up. Every time you select no, you will toggle to the next option within that setting. When you select yes or no, wait for a continuous tone and let the throttle go to neutral. If you selected yes, the ESC will go to the next setting.
To change to NiMH mode, you will need to go to the first setting. Remember, LiPo batteries must be used LiPo mode.
Vanguard AE-3. The Vanguard AE-3 is a brushless motor speed control. It comes preprogrammed in the “Auto-LiPo” mode. Like the AE-2, you can use the Castle-Link to program the ESC with your PC, but you can also manually program the ESC with your transmitter.
When programming, as a safety measure, remove the pinion from the motor. This will prevent the gears and/or vehicle from moving and causing damage to the vehicle or you. Turn the transmitter on and then connect a freshly charged battery to the ESC. Hold full throttle and then turn on the ESC. You will hear four tones from the ESC and then another four tones. After the second series of four tones, release the throttle. The ESC will beep twice indicating you’re in programming mode.
There are nine settings that can be adjusted. Each setting, in turn, has a varying number of options. You will use your transmitter’s throttle to select yes (full throttle) or no (full brake) for each option. When you select yes, the next setting will come up. Every time you select no, you will toggle to the next option within that setting. When you select yes or no, wait for a continuous tone and let the throttle go to neutral. If you selected yes, the ESC will go to the next setting.
To change to NiMH mode, you will need to go through settings one through six to get to setting seven, which changes the battery mode. Remember, LiPo batteries must be used LiPo mode.
Setting 1 Brake/Reverse Type
Option 1: With Reverse*
Option 2: Without Reverse
Option 3: Crawler Reverse. No delay from throttle to brake to reverse.
Setting 2 Brake Amount
Option 1: 25% Power
Option 2: 50% Power*
Option 3: 75% Power
Option 4: 100% Power
Setting 3 Reverse Amount
Option 1: 25% Power
Option 2: 50% Power*
Option 3: 75% Power
Option 4: 100% Power
Setting 4 Punch/Traction Control
Option 1: High
Option 2: Medium
Option 3: Low
Option 4: Lowest
Option 5: Disabled*
AE-5. The AE-5 is a brushed speed control and is by far the easiest ESC to program. To switch from the factory LiPo mode, remove the “jumper” and move it over one position. Not only is this ESC easy to program, it’s also waterproof.
AE-1. Axial’s AE-1 ESC does not have a LiPo cutoff. If you use LiPo batteries in a vehicle equipped with an AE-1 ESC you must use a separate LiPo low-voltage cut-off device. Axial does not sell a separate LiPo cut-off device, so the best choice would be to upgrade to an ESC such as the Axial AE-5 (see above), which is extremely easy to program and waterproof.
Store-bought RTR scale trucks are a blast; they’re already built and ready to get out on the trails as soon as your battery is charged. There are those, however, that love the extra challenge of scratch building their next scaler – pulling parts from multiple rigs to create a one-off design that suits their technical needs.
If you’re that scratch-built guy then this post is for you! We’ve gathered all our current transmissions and put together a little transmission guide complete with part numbers and specific details. This should help you choose the best transmission configuration for your custom build.
About a year ago, you may have noticed a project that popped up on YouTube created by HemiStorm RC, an Axial Yeti XXL. For a split second this may seem confusing because you’re probably asking yourself, does Axial make a Yeti XXL? Unfortunately that is not the case. However, HemiStorm had an idea that would technically produce the largest Yeti XL in existence by grafting two, YES TWO, Yeti XL’s together and appropriately calling it the “Yeti XXL.” Essentially the back half of one chassis was cut off just in front of the transmission while the front half of another chassis was cut off just behind the transmission thus giving the Yeti XXL two transmissions. It seems slightly odd, but when you toss in two Castle Creations Mamba Monster X ESC’s the idea starts to make sense. Each half of the vehicle is powered by its own esc and transmission allowing for the possibility of adding front or rear bias to the drivetrain. It’s an excellent idea considering the entire array of channel mixing capabilities within the Futaba 4PL radio he uses. To HemiStorm’s credit, this was a massive task to take on that required a bit of engineering know-how, some trial and error, and the acquisition of a few special tools. In order to properly tell the story behind the Yeti XXL, Hemistorm is going to be the best storyteller.
Think of this as a tutorial or timeline behind his Yeti XXL build. So grab a notepad, some snacks, and click the auto play button on your YouTube account to watch the entirety of his build process because it’s certainly worth a watch.
The entire Yeti XXL progress in one playlist:
Now that you’ve got your healthy dose of video behind what it took for HemiStorm to make the Yeti XXL, it’s time for photos. While Chris was in town for RCX he made a pitstop over to Axial HQ so we could get a closer look.
Chris de Graaf a.k.a. “HemiStorm” and Axial’s Rodney Wills having a few choice words.
It goes without saying, but HemiStorm you’ve truly built a one-of-a-kind vehicle. Keep up all the great work and if you want to follow Chris on his various social media platforms see the links below.
Slow motion video, long wheel travel, wheels tucking up into a Trophy Truck body mixed in with off road bashing is a lot like attempting to say “NO” to that last cookie in the cookie jar. It’s fair to assume that cookie didn’t stand a chance, just like this video had to be watched. If you’ve been following JPRC’s YouTube page you’ll notice he’s a fan of Trophy Trucks, if not, make sure to take a few moments and check out his page.
Given the opportunity to paint up a few SCORE® Retro Trophy Truck® bodies for the up coming body release, Axial staff nabbed a few bodies and took some creative liberty and ran with it. Lets be honest, wouldn’t have you? And from the looks of it each body has its own unique flare ranging from an old school Las Vegas race truck flare to budget Trophy Truck® with multi colored fender panels. Despite all the differences, all chose to use the full roll cage assembly for full effect. Here is a closer look into each vehicle.
Brandon’s Retro Truck Build
Contrasting colors with a fair amount of flare, more Rasta less Retro.
Randall’s Retro Truck Build
The Every Man’s Trophy Truck.
Jamie’s Retro Truck Build
Look familiar? If you watched “On the Loose in Baja” then you’ve certainly seen this truck. Classic Ford Racing color scheme.
John’s Retro Truck Build
And then there is te classic Retro Trophy Truck paint scheme littered with bass boat gold flake that screams early SCORE race days.
And just in case you missed “On the Loose in Baja”…
On the Loose in BajaWhat do you do when you’re in Mexico for the Score International Baja 1000 with you’ve a couple Yeti Trophy Trucks at your disposal… Let loose and have a great time.
Whenever I get a new vehicle, I like to take the first couple weeks to just drive it in box-stock form to learn about its traits; how it handles, any quirky nuances, etc. During this time I also take some time to review any hop ups that might become available, giving me an idea on how my long-term upgrade process is going to play out. Thankfully, the SCORE Trophy Truck shares the same platform as the Yeti Rock Racer, which means that there are a slew of performance goodies already available. Armed with a bag of aluminum bits, I decided it was time to install them prior to getting this rig all dirty. Not only did that make it a lot easier to deal with (read: no dirt!), it also looks much prettier in pictures. Time for an Axial Yeti SCORE Trophy Truck Full Option Build!
Here are the parts I’ll be installing in this article. I’ve got quite a bit of work ahead; shocks, gears, machined parts and turnbuckles. A full list of the parts I installed is included at the bottom of this article.
Since I’m going to need to remove the center transmission for upgrades, I disconnected the motor wires from the ESC. Pay attention to how the wires connect; if you have a photographic memory, you’re good to go. If not (like me), you can mark them to keep things straight. I put one silver mark for the A wire, 2 for the B and 3 for the C.
I’m going to be working on the front end of the SCORE TT first. I started by removing the top deck support brace. It requires the removal of 10 screws in two different lengths so, to keep things organized, I put them back in the holes after removal.
Once the top deck support brace has been lifted off, removal of the front clip is easy. There are 4 screws underneath the chassis and the two hinge pin screws. I also disconnected the fixed-length steering turnbuckles as well – I’m replacing them with adjustable ones.
Separate the gearbox from the shock tower by removing the 4 screws holding them together. I’m only working with the differential at this time so I set the rest of the front clip assembly aside. Note the orientation of the diff in the gearbox. You’ll want to make sure you re-install it the same way.
Next, I removed the differential and bevel gear assemblies from the gearbox. I’m replacing them with the AX30395 Heavy Duty Bevel Gear Set shown in the picture. One thing to notice is that the assemblies have straight cut gears; this design is pretty strong and easy to machine. The new HD versions are helical cut, or machined with a slight angle in them. These are great for high-torque applications like crawlers or, in this case, hardcore trophy trucks! To replace, remove the 4 screws on the diff to release the gear, set the new gear in place and re-install the 4 screws. If you’re the tinkering type, you might think about adding some optional fluid to the diff prior to putting it back together (I did, 1000wt). The HD bevel gear is a one-piece unit so replacing the stock part is a simple pull-and-replace operation. One final step I performed was to remove the rubber stops that are installed in each diff outdrive. If you hold the diff on its side, you’ll see them down inside there. These are used to keep the dogbones tight and prevent them from ejecting during a hard crash, however they hinder the up and down suspension movement slightly. Since I’ll be replacing the dogbones with universals, they’re not needed anymore.
I’m ditching the stock dogbone setup for a set of Axial’s AX31135 94mm Universal Axle Set. These come as a pair, are pre-assembled and slide right into place.
I re-assembled the front clip – the new shock tower to the gearbox and the front bumper to the tower. I left the shocks off for now since I was replacing them with a full set of Axial’s Icons. You can also see the aluminum upper shock mounts that are included with the aluminum shock tower.
For strength and additional tuning, I’m adding a full set of front adjustable turnbuckles (AX31249 Yeti Turnbuckle Set). This kit includes an excellent build sheet, so assembly is very easy. Just build the turnbuckles to the appropriate lengths and you’re good to go. I would suggest keeping them separate during the build so you don’t mix up the steering links with the camber links; the two are different.
Before attaching the front clip back on the TT, I need to do a little work on the transmission. I pulled it from the TT and removed the gear cover, motor, plastic backing plate and plastic motor mount.
I installed Axial’s AX31156 Machined Adjustable Motor Mount, a 2-piece unit that includes the main mount that attaches to the gearbox and a mount that attaches to the motor. The motor mount part swivels to adjust the gear mesh and uses an upper clamp to keep it securely in place. Because it’s aluminum, this system is SUPER strong and helps pull unwanted heat away from the motor. I re-attached the plastic backing plate followed by the spur gear assembly (I used Axial’s AX31161 32P 64T Steel Spur Gear and AX31164 Machined Slipper Plates in place of the stock parts). These upgrades look awesome and should make the gearbox virtually bulletproof. After I tightened everything up, I went ahead and re-installed the gearbox into the TT.
Time to get the front back together, so I started by sliding the front clip onto the chassis and securing with the 4 screws from underneath as well as the two hinge pins. I made sure to key the center universal into the outdrive located under the transmission. It’s a little tricky, so I would suggest rotating the transmission gears (using the back tires) until you see the slots in the outdrive; this will make it easier to key the universal. Next, I slid the front axles through the steering blocks, attaching the wheel hexes to keep them in place. I installed the steering and camber links, making sure to key the axle bones into the outdrives. A little care has to be taken here to make sure the axle bones stay inside the outdrive.
Now that the front is back on and looking good, it was time to move on to the rear clip and the installation of a lot of performance parts. The first thing I needed to do is separate the rear clip from the rest of the chassis; front cage screws, rear cage screws and the 4-link mounts. If you did it right, this is what you should be left with.
My first plan of attack is the rear differential. To extract it, I needed to remove the diff cover, the straight axle hub carriers and the axles (just pull them out slightly). I also removed the two plastic diff-capture plates that hold the diff in place. Note the orientation of the diff gear inside the housing.
Replacement of the diff gear and bevel gear is the same as the front. Once completed, re-assemble by inserting the diff gear, diff-capture plates and axles (key and slide back into place). I installed the optional AX30789 AR60 OCP Aluminum Straight Axle Hub Carrier.
I also installed Axial’s AX31245 Lower Link Plate Set. These also bolt right on using existing holes in the plastic links. I would suggest installing and tightening the two end screws while leaving the centermost pair loose. They can be tightened up when you re-install the shocks and anti-roll bar.
Here is the rear clip assembled with all of the aluminum parts installed. You can see I’ve also added the AX31166 Machined Shock Mount Plates, AX30830 AR60 OCP Machined Link Mounts and AX31167 Machined Sway Bar Clamps. The Machined Sway Bar Clamps are a little hard to see, but I’ve added some additional pictures at the end that help show their install. When re-attaching the rear clip back to the chassis, add some threadlocker to the screws that secure the aluminum 4-link mounts. This will help prevent the screws from backing out when you’re out having a good time.
While I loved the look of the King shocks, I couldn’t pass up installing a full set of Axial’s Icons. Per the included instructions, I built a set of front and rears and installed them in place of the Kings. I have an additional set of shocks to create a dual-shock setup, but I’m going to give it a whirl with the single shocks first. The dual-shock install (and tuning) will be for a later article. As you can see from the pictures, the aluminum parts look awesome and will provide additional strength as well as give the truck a bit more of a ‘factory’ look. Time for me to get outside and get this thing dirty!
If you didn’t already know, tires make the single biggest difference in the overall performance of a competition vehicle. A fast motor will increase top speed, but if you want lower lap times, if you want to be in front of the competition, if you want to win, it is absolutely essential you spend time to getting the right tire setup on your Axial Racing vehicle. This includes tread pattern, rubber compound, size, inserts and even, to some extent, wheels.
While all Axial Racing vehicles include high-performance scale tires, there is no single best tire. What works perfectly at one rock racing track simply may not work at all at another track. Also, track conditions change, so what worked at one point in a race day might not be the ideal choice later in the same day.
Rock racing is tricky because what works exceptionally well on rocks is unlikely to work on high-speed dirt sections and vice versa. It is essentially impossible to pick out a rock racing tire without making some sort of compromise. The specific track you are racing on will determine which way you want to compromise performance.
The tread is the most obvious feature of a tire. All of the other features in a tire design matter to varying degrees, but it’s hard to argue that tread pattern makes a big difference.
Treads with taller, flexible lugs can sometimes be beneficial on rocks, but they are unlikely to do well on typical hard racing surfaces where the tread easily folds over. When the lug folds over, it provides inconsistent and unpredictable handling as they can slightly squirm around. If a track has a lot of silt, which is very common, tall lugs do help. Most racing-specific tires, however, have short lugs, so if the rock racing track you’re competing on has a lot of fast sections, select a tires with smaller, closer-spaced lugs.
Large voids (open spaces) between lugs help keep tires from clogging with soft, wet dirt. If the track is muddy due to weather conditions or heavy watering by the track crew, consider a tire with large spaces between the treads such as the Axial BFGoodrich Krawler T/A tire.
Another part of the tread to look at is the sidewall. Tires such as the Axial Maxxis Trepador and Axial Ripsaw have significant tread wrapping down the side of the tire carcass. These side treads can be a huge advantage on the rocky section and typically won’t impact handling on the fast sections.
Don’t be afraid to mix and match tires to achieve the desired handling. Often rock racers have a hard time with squirrelly handling on the fast sections and at the start. Going with a less aggressive front tire can help reduce oversteer. If the car slides (not spins out) in the corners, it will benefit a more aggressive front tire and might need more traction overall.
There are numerous rubber compounds to choose from. Softer compounds such as Axial’s R35 compound (white dot) are softer and stickier. Soft compounds provide more traction, but wear faster. A soft compound such as R35 is almost always better for rock racing.
In the same way treads can be mixed and matched, different compounds can be used the front compared to the rear. It might make sense to start with R35 compound with the rear tires only.
Often, when selecting tires for rock crawling, the focus is on tire height, but width is just as important when choosing a rock racing tire. In general, and with all things being equal, a wider tire has an increased contact patch and will provide more traction. Narrow tires up front teamed up with wider rear tires can be an ideal setup. This is especially worth trying if your truck is struggling to track well in the corners.
While width is important when looking for the right front to rear balance, height is still important. The main benefit of taller tires is increased ground clearance. Taller tires also have taller sidewalls since we only use a few wheel sizes in R/C. Taller sidewalls have no benefit on the fast sections, but tall sidewalls do allow for a more flexible tire that can wrap around rocks and aid in climbing.
In full-size tires, compressed air supports the tire. There are a few exceptions, of course. In R/C, foam inserts replaces the air, and just like the air inside a full-size tire, the foam supports the tire. Firmer foam is like higher PSI and softer foam is like less PSI.
Foam can be divided into four groups: open-cell, closed cell, memory, and multi-stage.
Open-cell foam is the most common type of foam found in R/C. Not all open-cell foam is the same; there are countless varieties. This is the same for all of the foam types. Axial Racing includes a medium density (firmness) foam insert.
Closed-cell foam is molded foam and in the last five years has become the most common type of foam used with racing vehicles. A solid closed-cell insert is, however, almost always too firm to work well for rock racing.
Memory foam is often used in rock crawling, but it can have some ill effects when rock racing. Memory foam is heavier than both open- and closed-cell foam. This helps with rock crawling, but can actually cause accelerated parts wear. Unlike traditional foam, memory foam is slow to return to its original shape after encountering an obstacle. This characteristic of memory foam helps when rock crawling where going slow is the norm. The memory foam conforms to and wraps around obstacles. When rock racing, if memory foam is compressed it will cause an out-of-balance tires and erratic handling.
Multi-stage foams use more than one type of foam and allow you to have a “best of both worlds” setup. Just about any combination is possible, but the best setup for rock racing would be a closed-cell inner ring surrounded by an open-cell outer ring.
How the foam fits inside the tire also impacts how firm it feels. For rock racing, it is best to use a foam insert properly sized to the tire. An oversized foam insert will make the foam firmer than possibly desired and an undersized foam will provide erratic handling as it moves around inside the tire. In high-speed racing, a slight air gap (space between outside top of the foam and inside of the tread are) will increase traction without hampering handling as long air gap isn’t too large. Creating a consistent air gap when using open-cell foam can be difficult, but with careful attention to detail it is possible.
An important item to consider is that foam inserts wear out. Sometimes tires might not show a lot of visible wear, but the inserts inside have broken down. Open-cell foam wears out the fastest. Often simply squeezing a tire doesn’t demonstrate how the foam is holding up. Instead, squeeze all of the tires and make sure the foam rebounds at the same in rate in all of the tires. Carefully feel the tires to see if the is an increased gap between the tire and the foam insert. If you’re using bead lock wheels, disassembling the tires and wheels may be in order.
Where rock crawlers often favor heavier aluminum wheels, lightweight wheels are best rock racing. Increasing rotational mass, such as with heavy wheels, is never desirable on a high-speed vehicle. In fact, lightweight and more flexible wheels will most likely improve handling over bumps and jumps.
While bead lock wheels have the advantages of being easily reused and unlikely to fail (have a tire come apart) if properly installed, they are heavier. Glue-up style one-piece wheels are often appropriately flexible and lightweight, which, as stated, are good qualities for racing.
Straight out of the box, the Yeti Trophy Truck features gearing (16T pinion / 64T spur gear) best suited for extended run time on a 3S LiPo 5000 mAh battery. While this gearing yields a healthy amount of run time on both 2S and 3S (perfect for extended outdoor adventures), as customers, we are always looking for MORE SPEED. This is likely due to the fact that once people experience just how capable a Yeti Trophy Truck is in the wild, the tendency to want more speed becomes an overwhelming thought. Truth is… it can handle more, although more than what Axial offers with regard to available pinion gears.
After extensive testing with a variety of battery / pinion / spur gear combinations, we came to the following conclusion for best run time and speed on 2S and 3S:
2S 5000 mAh – 21T pinion / 64T spur gear • top speed 20mph • 15 minutes of run time 3S 5000 mAh - 21T pinion / 64T spur gear • top speed 32mph • 20 minutes of run time