RC Motor Sizes Explained: What Size Numbers like 3650 and KV Ratings Really Mean
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Choosing the right RC motor can feel confusing when you start seeing numbers like 3650, 2845, 540, 3300KV, 4400KV and 7200KV.
If you’re new to the hobby, it’s not obvious what any of this means — but once you understand the basics, it all becomes simple.
Here’s a breakdown that will help you understand the motors inside the models we sell at The Truck Monster, and how to choose the right power system for your RC car.
What Do Motor Size Numbers Mean? (3650, 2845, 540 etc.)
Brushless motor sizes are usually written as four digits, such as:
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3650
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2845
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2435
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3660
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4074
These four digits describe the physical size of the motor:
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First two digits = motor diameter in mm
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Last two digits = motor length in mm
So:
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3650 motor → 36mm diameter, 50mm length
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2845 motor → 28mm diameter, 45mm length
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3660 motor → 36mm diameter, 60mm length
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2435 motor → 24mm diameter, 35mm length
Larger motors = more torque and more cooling capacity.
Smaller motors = lighter, more efficient, used in 1/18–1/28 scale cars.
This is why:
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The MJX Hyper Go 16208 uses a 2845 brushless motor — perfect for 1/16 scale.
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Bigger 1/10 scale models often use 3650 or 3660 motors.
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Micro crawlers like FMS FCX24M use tiny outrunners designed for torque, not speed.
The Difference Between Inrunners and Outrunners
Inrunner motors
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Used in most RC cars
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Rotor spins inside a stationary can
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High RPM, lower torque
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Perfect for speed and acceleration
Outrunner motors
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Used in many small crawlers and planes
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Outer can spins
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High torque, lower RPM
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Great for crawling and slow control
For example, the FMS 1/24 Defender FCX24M uses a crawler-tuned outrunner-style motor, built for control instead of top speed.
What Does KV Mean? (3300KV, 4400KV, 7200KV)
KV is one of the most misunderstood numbers in RC.
KV = RPM per volt.
The higher the KV, the faster the motor spins — but with less torque.
For example:
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3300KV motor → spins at 3300 RPM per volt
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4400KV motor → spins at 4400 RPM per volt
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7200KV motor → extremely high RPM, low torque
So on a 2S LiPo (7.4V):
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3300KV → ~24,000 RPM
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4400KV → ~32,500 RPM
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7200KV → ~53,000 RPM
On a 3S LiPo (11.1V):
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3300KV → ~36,600 RPM
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4400KV → ~48,800 RPM
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7200KV → ~80,000 RPM (not suitable for most RC cars)
High KV vs Low KV: Which Is Better?
High KV (e.g., 4400KV+)
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Very fast
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Less torque
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More heat
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Best for on-road and drift
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Needs good gearing
Low KV (e.g., 1800KV–3300KV)
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More torque
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Cooler running
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Better acceleration
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Ideal for off-road and bashing
This is why:
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The MJX Hyper Go 14301 Drift/Rally uses a high-KV motor for strong top speed.
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The MJX Hyper Go 16208 uses a balanced KV to keep temperatures low while bashing off-road.
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Crawlers like the FMS Defender rely on very low KV for precise slow-speed torque.
Motor Size + KV Rating = The Motor’s True Character
Think of the two numbers like this:
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Size (3650, 2845, etc.) = Strength
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KV (3300KV, 4400KV, etc.) = Speed
So a big motor + low KV = torque monster (ideal for big off-road trucks)
A large motor + high KV = extreme speed (on-road missiles)
A small motor + high KV = lightweight rocket (1/16 or 1/14 drift cars)
A small motor + low KV = perfect crawler motor
This explains why models can perform so differently despite being of a similar size and running on the same number of cells:
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16208 (1/16 basher) → mid-KV 2845 for balanced torque & speed
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14301 (1/14 rally/drift) → high-KV motor for rapid acceleration and high top speed
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FMS 1/24 Defender → tiny, low-KV outrunner for fine control and climbing torque
Choosing the Right Motor for Your RC Car
Here’s a quick reference:
For Off-Road Bashing (Grass, Dirt, Gravel)
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Motor size: 2845, 3650, 3660
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KV: 2800KV–3800KV
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Example: MJX Hyper Go 16208
For On-Road and Drift
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Motor size: 2435, 2845, 3650
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KV: 4000KV–6000KV
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Example: MJX Hyper Go 14301
For Crawling
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Motor type: Outrunner or low-KV brushed
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KV: Low KV torque motors
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Example: FMS 1/24 Defender D110 FCX24M
Final Thoughts: Motor Numbers Matter More Than You Think
Understanding motor sizes and KV ratings helps you choose the right RC for your terrain and driving style. Bigger numbers don’t always mean better — it depends on how you use the car.
That’s why at The Truck Monster, we test everything we sell.
When you see us recommending a model like the:
…it’s because the motor system genuinely matches what the car is designed to do.