The Arrma Granite Grom starts as a plucky 1/18-scale monster truck, but with some serious upgrades—like the Furitek Scorpion brushless motor, Powerhobby PH60 servo, Arrma aluminum shocks, metal diffs, and a steel universal kit—it’s morphed into a tiny titan that laughs at punishment. I’ve been thrashing mine hard, and here’s the rundown on how this modded Grom holds up.
First Impressions
Out of the box, the Grom’s got that Arrma grit: a sturdy composite chassis, chunky dBoots Fortress tires, and a clipless body that’s a cinch to remove. At 13 inches long, it’s backpack-friendly, and the stock 2S LiPo with USB-C charger makes it an easy RTR package. Mine shipped with a higher front end than rear—a “raked” stance that looked cool but threw off the balance. Stock, it’s a solid basher, but with these upgrades, it’s a whole different beast.
Performance: Stock vs. Fully Upgraded
Stock, the MEGA 380 brushed motor and 4WD drivetrain hit 20-25 mph—decent for a beginner rig. The suspension was okay for small jumps, but that front-high stance made it understeer and pitch back in the air. Here’s how the upgrades flipped the script, with speed details on 2S and 3S using the stock 16T pinion:
- Furitek Scorpion Brushless Motor (5600kV) (Aftermarket, no Arrma part number; compatible with ARA310941 power module upgrade): Ditching the brushed motor for this sensored brushless setup (with matching ESC) turned the Grom into a rocket. The 5600kV rating means RPM per volt, and with the stock 16T pinion and 57T spur gear (3.56:1 ratio), speeds scale with battery voltage. Real-world factors—drag, weight (~2.5 lbs), and ~80% efficiency—trim the theoretical max, but it’s still fast. The motor and ESC are fully programmable via a free iPhone or Android app—I dialed the punch setting down to 1 to tame the initial kick, making it smoother off the line, especially on 3S. Calibrating the speed control to the Spektrum iXSR radio was key; I noticed a huge power boost afterward, unlocking the full potential—don’t skip this step! The sensored motor’s smoothness gives awesome air control too—jumps feel precise and predictable, no jerky nonsense.
- On 2S (7.4V): Theoretical motor RPM is 41,440 (5600 × 7.4). Divide by the 3.56:1 gear ratio (~11,634 wheel RPM), and with ~7.85” tire circumference, that’s ~17.3 ft/s or ~11,800 ft/min. Converted, theoretical top speed is ~43.3 mph, but losses drop it to 33-38 mph. I’ve hit ~35 mph on pavement—plenty quick for this little rig.
- On 3S (11.1V): Theoretical RPM jumps to 62,160 (5600 × 11.1). Same gearing gives ~17,461 wheel RPM, or ~25.9 ft/s (~15,540 ft/min), equating to ~64.9 mph theoretically. Real-world caps it at 48-53 mph due to heat, drag, and drivetrain limits. I’ve clocked ~50 mph—nuts for a 1/18-scale truck, and it’s a handful to control! Not available on Parkflyers; check Furitek’s site.
- Optional Spektrum 3S Battery: For 3S power, I’ve also run the Spektrum 11.1V 2200mAh 3S 30C Smart LiPo Battery with IC3 Connector (SPMX22003S30). It’s a compact, affordable option that fits the Grom’s battery tray and works with the iXSR’s telemetry. Priced at ~$54.99 (as of March 12, 2025, from Horizon Hobby or Amazon), it’s lighter than bigger 3S packs (180g vs. 300g+ for 5000mAh options), keeping the rig nimble. On 3S with this battery, I still hit 48-50 mph, and the Smart tech auto-discharges to storage voltage—handy for maintenance. It’s not the punchiest 3S pack (30C vs. 50C+ alternatives), but it’s reliable and budget-friendly for casual bashing. Available on Parkflyers as a similar Spektrum battery.
- Powerhobby PH60 Servo (Aftermarket, no Arrma part number; replaces ARA340181 stock servo): The stock steering felt mushy under load; the PH60 is a beast—fast, precise, and unfazed by the brushless torque. Corners are tight, and mid-air corrections are spot-on. You’ll need a Hot Racing Micro 25T Servo Saver (part #HRAMG48025) available on Parkflyers to make it work right—for some reason, the Powerhobby-branded version incompatible, Parkflyers link comes with the wrong hardware and won’t fit properly. The Hot Racing one bolts up perfectly and handles the PH60’s power like a champ. Also, the Furitek Carbon Fiber Servo Mount (part #FUR2028) available on Parkflyers is a must to secure it properly—stock mounting won’t cut it with this servo’s grunt.
- Arrma Aluminum Shock Set (ARA330706 - Aluminum Shock Set, Grom-compatible): Swapped the stock shocks for Arrma’s aluminum upgrade—sleek, durable, and filled with Traxxas 80wt shock oil (Traxxas 5037, 1000cSt, 60cc silicone) to slow rebound speed. I upped it from the stock ~40wt to 80wt available on Parkflyers, and it pairs perfectly with the spring cut (see below) to keep it level and soak up landings—no more bottoming out under the brushless power. The heavier oil makes it settle smoother after jumps and keeps it planted on rough terrain, a noticeable step up from the stock bounciness. Shocks available on Parkflyers.
- Metal Diffs (ARA310944 - Metal Differential Gear Set): The stock diffs were a known weak point, especially with brushless power. Upgraded to all-metal differentials, and they’re bulletproof—zero slop, no grinding, just pure power to the wheels. For better launch off the line, swap the rear diff fluid to Kyosho 1000-weight grease—it hooks up harder and gets you moving quick. Available on Parkflyers.
- Steel Universal Kit (ARA310943 - Steel Driveshaft Set): Ditched the stock driveshafts for a steel universal setup. Smoother power transfer, no binding, and they shrug off high-speed torque like it’s nothing. Perfect match for the Scorpion motor. Available on Parkflyers.
This combo is wild. We swapped the stock Spektrum SLT2 radio for the Spektrum iXSR—a premium upgrade with sharper response, customizable settings, and telemetry to monitor speed and battery life. The throttle limits (50% and 75%) are clutch for taming that 50 mph 3S beast mode. Jumps are long and flat, cornering’s razor-sharp, and it eats terrain for breakfast.
Durability: Built Like a Tank
Stock, the Grom could take a beating—bumps and flips barely scratched it. With these mods, it’s a fortress. The steel universals and metal diffs handle the brushless grunt without a whimper, and the Arrma aluminum shocks soak up abuse that’d shatter plastic. I’ve sent it off ramps, slammed it into roots, and flipped it at speed—no major damage. The stock plastic arms hold up fine so far, and the body mounts flex a bit under extreme hits, but the chassis and drivetrain are rock-solid. The stock weak links are gone—this thing’s ready for war.
The Ride Height Fix
That front-high “raked” stance was a handling buzzkill stock—weight shifted back, making it twitchy and nose-up on jumps. The stock setup had positive droop—front arms angled upward from the chassis—which threw off balance and made landings sketchy. We fixed it by cutting the front springs just enough to level the chassis with the rear, keeping the front arms parallel to the ground. Paired with the Arrma aluminum shocks (ARA330706) running Traxxas 80wt oil, this tweak is a game-changer. The car’s now dead even, and the difference is night and day. Jumps are way better—no more pitching back mid-air; it flies flat and lands smooth, even at 50 mph on 3S, with the slower rebound keeping it controlled on touchdown. Handling’s sharper too—eliminating that droop kills the understeer, keeps the front tires planted, and makes high-speed turns feel locked-in. Stability’s through the roof, especially with the brushless power pushing it hard.
Power-to-Weight Breakdown: Stock vs. Upgraded
Here’s how the upgrades stack up in power and weight. The brushless swap saves ~20g on the motor, but durability upgrades add weight—worth it for the power jump from 60W stock to 200W (2S) or 300W (3S). Check the chart:
|
Setup |
Weight |
Power |
Power-to-Weight |
Weight Change |
|
Stock (2S) |
1.13 kg (2.5 lbs) |
60W |
53.1 W/kg |
Baseline (0g) |
|
Upgraded (2S) |
1.18 kg (2.6 lbs) |
200W |
169.5 W/kg |
+50g |
|
Upgraded (3S) |
1.23 kg (2.71 lbs) |
300W |
243.9 W/kg |
+100g |
Upgraded 2S triples the stock power-to-weight (3.2x), while 3S quadruples it (4.6x), driving that 35-50 mph leap. The ~50g (2S) or ~100g (3S) added weight comes from beefier shocks (+20g), diffs (+20g), driveshafts (+20g), servo (+5g), servo saver (+5g), and the 3S battery swap (+50g).
Sales Snapshot
The Granite Grom’s a hot ticket from Horizon Hobby—its compact size and upgrade potential have made it a go-to for bashers since its release. Exact 2025 sales figures aren’t public yet, but its popularity is clear from the buzz and aftermarket support. [Insert current yearly sales here if available from Horizon Hobby or your records—e.g., “Horizon Hobby reports X units sold in 2025 so far.”] Either way, it’s a small-scale monster with big demand.
Pros
- Compact size, insane durability
- Stock RTR is affordable (~$130-$150), upgrades unlock next-level potential
- Furitek Scorpion + PH60 servo = speed and control
- Metal diffs and steel universals make it tough as hell
- Handles like a pro rig once leveled
Cons
- Stock diffs and driveshafts can’t handle brushless power (fixed with upgrades)
- Ride height needed cutting to fix rake (simple tweak)
- Weight creeps up with upgrades—still worth it
Final Thoughts
The Arrma Granite Grom is a gem stock—a tough, fun mini basher for the price. But load it with the Furitek Scorpion brushless motor, Powerhobby PH60 servo, Arrma aluminum shocks, metal diffs, and a steel universal kit, and it’s a pocket-sized juggernaut. Cutting the front springs to ditch that raked stance and positive droop was key—now it’s fast, precise, and damn near unbreakable. You’re looking at $150 stock plus maybe $250-$300 in upgrades—pricey, but you get a rig that outpunches most 1/10-scale trucks. I’m calling it a 4.8 out of 5—stock it’s great, fully modded it’s a legend. Just don’t blame me when you can’t stop driving it!
Where to Get It
Ready to grab your own Granite Grom and start modding? Buy Now at Parkflyers. For a custom rig like this, call Marc from Parkflyers at 1-800-470-8932 (ask for Marc) or email Marc@parkflyers.com. Swing by the hobby shop at 55 Park Ave South, Lakewood, NJ 08701—hours are 11-5 PM, closed Saturday. Marc and the crew can hook you up with these upgrades and more, tailored to your style.
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Perfect Backpacks to Carry Your Granite Grom
The Grom’s compact (13 x 8 x 5 inches) and light (~2.5-2.7 lbs with upgrades), so here are some slick backpacks to haul it with ease and style, plus room for the radio, batteries, and tools:
- Cabin Max Metz 44L Carry-On Backpack (~$40-$50): 20 x 16 x 8 inches, 44L. Spacious, lightweight (1.5 lbs), and stylish—fits the Grom and all gear. Not waterproof, but affordable and sleek.
- SwissGear 1900 Scansmart TSA Laptop Backpack (~$80-$100): 18.5 x 13.5 x 9 inches, 31L. Snug fit for the Grom, with a laptop sleeve for the radio. Water-resistant, padded, and urban-chic, though heavier (3.2 lbs).
- Ogio Alpha Core Convoy 320 Backpack (~$90-$120): 19.5 x 14 x 9 inches, 32L. Rugged and roomy, with MOLLE webbing for extras. Tough Cordura build, great for bashing, but pricey.
- Herschel Little America (Mid-Volume) (~$100-$120): 17 x 11.25 x 5.5 inches, 17L. Tight fit for the Grom, super stylish with retro vibes. Light (1.8 lbs), but less rugged and cozy for extras.
- Sandpiper of California Bugout Bag (~$90-$110): 20 x 15 x 10 inches, 36L. Big and tough, swallows the Grom and gear with MOLLE options. Heavy (3.5 lbs), but a bashing beast.
These keep the total load (Grom + gear ~5 lbs) comfy under 10 lbs. Marc at Parkflyers might stock similar bags—call 1-800-470-8932 to check!