▶ How to use this simulator
click to collapse
1
Weigh your car
Weigh the car fully assembled with axles and wheels, but without the CO₂ cartridge. The 23g empty cartridge shell is added automatically by the sim.
scale / balance
2
Measure your wheels
Diameter (front and rear), mass of each wheel individually, and the axle bore diameter. Wheels are modelled as annular discs (PLA with bore hole) for rotational inertia.
callipers + scale
3
Measure frontal area & Cd
Trace the front of your car onto graph paper and count squares. Use the Cd preset closest to your body shape, or enter a measured value.
graph paper / wind tunnel
4
Select rolling resistance
Pick the surface type your car will race on. μr is the rolling resistance coefficient — it captures friction between wheels and track throughout the entire run.
track inspection
5
Set track length
Enter your competition track length. The sim uses a standard 8g Pitsco cartridge with a measured thrust curve — no cartridge setup needed.
ruler / tape measure
💡 Physics model: Euler integration at dt=0.0001s. Thrust-proportional CO₂ mass depletion conserving total impulse. Dynamic m_eff (chassis + CO₂ + annular-disc wheel inertia + optional axle inertia). Track rolling resistance, bore friction (static axle), and body bearing friction (dynamic axle) all update each timestep. Most reliable for comparing designs rather than predicting exact times.
Car Body
▶
g
Cd measures how easily air flows around your car. Lower is faster. Most CO₂ dragsters with exposed wheels fall between 0.4 and 0.6.
dim.
Cross-section area head-on. In Fusion 360: sketch on the front face, use Project to trace the outline, then check the sketch area in the bottom-right corner.
mm²
Wheels
▶
Front Wheels
mm
g
Rear Wheels
mm
g
The diameter of the hole through the centre of each wheel. Measure with callipers. PLA wheels are modelled as annular discs: I = ½m(R_outer² + R_bore²). A larger bore pushes mass further from the axis, increasing rotational inertia. Typical 1/8" steel axle → bore ≈ 3.2–3.5 mm.
mm
I = ½m(R² + r_bore²) · same bore applied to all four wheels
Axles
▶
Wheels spin / axle fixed: The axle is glued or press-fit into the car body and does not rotate. Only the wheels spin — axle inertia adds nothing.

Axle spins with wheels: The axle is free to rotate and turns with the wheels. Both the wheel and axle inertia must be overcome at launch. Solid-cylinder axle: I = ½mr², contributing an extra ½m_axle effective mass per axle.
Outside diameter of the steel axle rod. Standard CO₂ dragster axles are 1/8" (3.175 mm). Used to calculate bore friction: F_bore = μ_bore × m × g × (r_axle / r_wheel).
mm
Friction coefficient (μ) between the PLA wheel bore and the steel axle. Dry PLA-on-steel is ~0.25. Graphite powder reduces this to ~0.10.
F_bore = μ_bore × m(t) × g × (r_axle/r_wheel) — weighted 40/60 front/rear.
Rolling Resistance
▶
Rolling resistance coefficient (μr) captures energy lost as wheels flex and deform against the track. F_roll = μr × m × g. Smooth aluminium gives the lowest values.
Froll = μr × m(t) × g — updates each step as CO₂ mass depletes.
CO₂ & Environment
▶
Standard 8g CO₂ cartridge. Thrust curve fitted to Pitsco 8g measured data.
m
Assumes smooth, flat surface. CO₂ mass depletes proportionally to instantaneous thrust.
Predicted Finish Time
—
seconds · see model note below
Peak Speed
—
m/s · — km/h
Peak Accel
—
G's at launch · — m/s²
Speed & Distance vs Time
Speed (m/s)
Distance (m)
◎
Configure inputs and run simulation
CO₂ Thrust Curve
Thrust (N)
◎
Run simulation to see thrust curve
Race Replay
◎
Save runs to see replay
Run simulation to see model note.
What's slowing your car down? explain these forces
At Launch
Wheel Spin-up
—
Throughout Race
Track Rolling
—
Bore Friction
—
Body Bearing
—
At Peak Speed
Air Resistance
—
Saved Runs
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No saved runs yet