Walk into any RC discussion forum and you'll find two camps: the "upgrade everything to aluminium" crowd and the "plastic is fine, you're wasting money" crowd. Both are partially right. The truth — as usual — is more nuanced. Some plastic parts genuinely work better than aluminium alternatives. Others are false economy. Here's an honest breakdown.
The Design Intent Behind Plastic RC Parts
Traxxas engineers aren't cutting corners when they spec plastic steering knuckles or shock towers. It's a deliberate engineering decision. Plastic parts are designed to be sacrificial — they're the weak link that absorbs energy and breaks before more expensive components (transmission, motor, ESC) do.
At 2S LiPo power levels and moderate bashing, this philosophy is sound. You break a $9 plastic knuckle instead of a $60 gearbox. The system works. Traxxas even sells the replacement parts cheaply to support this model.
The logic starts to break down at higher power levels (3S+), on harder terrain (concrete, packed gravel, rocks), and with repeated high-energy impacts. At that point, you're replacing the same plastic parts repeatedly, the "cheap sacrifice" is no longer cheap, and the cumulative stress on connected components from repeated impacts starts to matter.
This is the core of the upgrade argument: not that aluminium is inherently better, but that at a certain intensity of use, the sacrificial model stops being economical.
What Aluminium Actually Does Better
Aluminium CNC parts offer several genuine advantages over plastic:
- Rigidity: Aluminium doesn't flex under load. This maintains geometry — camber, toe, caster — consistently during high-speed or high-load situations. Plastic flex is small but real, and it changes your handling baseline constantly.
- Crash resistance: Aluminium deforms rather than shattering. A crashed aluminium knuckle may bend slightly; a plastic one typically shatters or cracks through a wall, requiring full replacement.
- Dimensional stability: Aluminium doesn't creep or warp under heat and load the way some plastics do. Motor heat, sun on a hot day, repeated load cycles — aluminium holds its shape.
- Lifespan: Properly anodised aluminium parts in non-crash applications last essentially forever. Thread engagement is better, hinge pin bores don't wear oval as quickly.
When these properties matter to your specific use case, aluminium is worth it. When they don't, you may be spending money unnecessarily.
Parts Where Aluminium Makes a Huge Difference
These are the upgrades with the clearest cost-benefit case.
Steering Knuckles
The front steering knuckles on any Slash or Arrma truck take the first direct impact on frontal collisions. They're in the firing line every time you stack into a kerb. Plastic knuckles crack and break repeatedly. Aluminium CNC knuckles take the same hits without breaking. This is the clearest case for upgrading — the part that breaks most often, most directly replaced with a part that doesn't. The ROI on aluminium knuckles is fast.
Shock Towers
Shock towers take repeated stress on every landing — not catastrophic crash force, but the cyclic stress of hundreds of jumps. Plastic shock towers develop micro-cracks over time and eventually fail — often mid-bash when you're far from home. Aluminium shock towers handle the same cyclic stress indefinitely. They also hold shock positions precisely, which affects handling consistency.
C-Hubs and Steering Assembly
C-hubs are a wear item in plastic form — the hinge pins wear the plastic bore oval over time, introducing slop into your front steering. That slop feels like vague, unpredictable steering that worsens gradually. Aluminium C-hubs maintain their bore diameter essentially permanently, keeping front-end steering precise for years. This is a durability upgrade with a clear handling benefit.
Bulkhead
The front and rear bulkheads are the structural spine of the truck. In a hard crash, plastic bulkheads can crack or shear, misaligning the drivetrain. Aluminium bulkheads absorb crash energy without structural failure, protecting the transmission and differential. This is the "insurance policy" upgrade for trucks running at high power.
Parts Where the Upgrade Is Nice but Not Essential
These upgrades provide real benefits, but the urgency is lower — buy them when budget allows rather than first.
Battery Hold-Down
An aluminium battery plate is stiffer and more secure than a strap, but the stock system works fine in practice. This is a quality-of-life upgrade. The battery will be protected adequately either way; aluminium just feels and works better.
Servo Mount
An aluminium servo mount eliminates steering flex from a loose servo position. The benefit is more about precision and feel than durability — the stock plastic mount doesn't typically break, it just allows slight steering play under load. Worth doing, but not urgent unless you're running at 3S or above and want precise handling.
Motor Plate
Consistent motor mesh matters more at higher power. An aluminium motor plate keeps the motor-to-spur gear mesh constant under load. At 2S bashing this is minor. At 3S or above, it's a meaningful upgrade that reduces noise and wear on both gears.
Parts Where You Should Stick with Stock
This is where many hobbyists waste money. Some plastic parts are deliberately plastic for good reason.
Chassis Rails (Tub Chassis Trucks)
The Slash uses a tub chassis with flex engineered into the design. The flex acts as a torsional spring, keeping all four wheels on the ground over uneven terrain. Stiffening the chassis with aluminium rails or braces removes this flex and can actually make the truck handle worse on rough terrain. Don't brace the chassis unless you're building a race setup on flat surfaces.
Body Posts
Body posts are designed to snap before the body cracks. They're a fuse. Aluminium body posts that don't snap transfer crash energy to the body itself, cracking or ripping the body instead. Stock plastic body posts are correct here — they sacrifice themselves to protect the body.
Some Suspension Arms
This one is controversial. Aluminium suspension arms don't snap — but they bend on hard impacts, and a bent aluminium arm causes misalignment that's hard to spot and affects handling. A broken plastic arm is obvious and cheap to replace. In some scenarios, particularly heavy bashing on rough terrain, stock plastic arms fail in a more obvious and manageable way than bent aluminium. Know your use case.
The Value Equation — What's the ROI?
Here's a practical comparison for Australian hobbyists:
- Stock plastic steering knuckle: ~$9–12. Replaced every 3–4 sessions of hard bashing = $36–48 per year.
- Aluminium CNC knuckle: ~$28–35. Lasts 2–3+ years with normal use.
In 12–18 months of bashing, the aluminium knuckle has paid for itself versus replacing plastic repeatedly. The same maths applies to shock towers and C-hubs. Parts that break repeatedly are excellent candidates for upgrade. Parts that rarely break are lower priority.
Focus your budget on the parts that actually fail on your specific truck with your specific use patterns. Then work outward from there.
The Bottom Line
Aluminium is definitively better in direct impact zones (knuckles, bulkheads), cyclic stress zones (shock towers), and precision wear zones (C-hubs, motor plate at high power). It's marginal or counterproductive in deliberately flexible or sacrificial components (chassis, body posts, some arms).
Upgrade strategically, not comprehensively. Your truck will be faster, more durable, and better-feeling — without spending money on parts that didn't need changing.
Browse upgrade parts for your Slash: Traxxas Slash Upgrades