Fan car suction calculator
Put in a car’s weight, the floor area its skirts seal and how many G you want, and see how much lower the air pressure under the floor has to be, as in Tesla’s new Roadster driving upside down.
- Air under the floor
- 10.5% lower
- Air pressure under a 3.5 m² floor, against the air around the car at sea level
- Pull
- 3,800 kg
- 2 G on a 1,900 kg car
- Pressure difference
- 10.6 kPa
- 106 millibars, or 1,086 kg on every square metre of floor
- Upside down, left pressing the tyres on
- 1,900 kg
- The same as its weight on flat ground, so the tyres grip as they would on a normal road
To pull a 1,900 kg car down with 2 G, the fans have to take away 3,800 kg of force. Spread over 3.5 m² of floor, that’s 1,086 kg on every square metre, so the air under the car has to be about 10.5% below the air around it. Upside down, gravity pulls the car off the ceiling with its own weight, which leaves 1,900 kg pressing the tyres on. This assumes the skirts seal perfectly; real cars leak, so the fans have to work harder.
G here means multiples of the car’s own weight. The sum uses standard sea-level air pressure, 101,325 pascals, and standard gravity, and assumes the skirts seal the floor perfectly. Higher up, the air pressure is lower, so the same pull takes a bigger share of it. Tesla hasn’t published the Roadster’s floor area or the weight of the car that drove upside down, so the starting numbers are our estimates.
What goes in
Put in the car’s weight, the area of floor its skirts seal against the road, and how many G you want the fans to pull it down with. 1 G is the car’s own weight; 2 G is twice that.
What the result means
Air presses on everything at about 10.33 tonnes per square metre at sea level. Fans that suck air out from under a sealed floor take some of that away underneath, so the air on top pushes the car onto the road. The calculator shows how much lower the pressure under the floor has to be, as a share of the air pressure around the car, and the same in kilopascals and millibars.
Upside down, gravity pulls the car off the ceiling with its own weight. At exactly 1 G the tyres carry nothing and can’t grip. At 2 G they’re pressed on as hard as they would be on a normal road.
During the upside-down run at its October 2026 event, Tesla’s screen showed about 4,700 kg of downforce. Tesla hasn’t said how big the Roadster’s sealed floor is. If it’s 3 to 4 square metres, our estimate, that needs the air underneath about 11 to 15% below the air around it.
The figures behind it
The pull is the weight times the G, and pressure is force divided by area, using standard gravity (9.80665 m/s²) and standard sea-level air pressure (101,325 pascals). 4,700 kg over 3 m² is 15.2% lower, over 4 m² it’s 11.4%, and a 1,900 kg car at 2 G over 3.5 m² is 10.5%. The sum assumes a perfect seal; real skirts leak, so the fans have to keep pumping air out.
Sources
- Tesla: Roadster page (the fan and ground-sealing system), and the Roadster event livestream, whose on-screen readout during the inverted ramp run showed about 4,700 kg of downforce
- NIST: standard acceleration of gravity (9.80665 m/s², exact) and standard atmosphere (101,325 Pa, exact)