Motor Air Gap
Motor air gap is the physical clearance between the stationary stator and rotating rotor across which the motor's magnetic field must pass.
Why it matters
Air has much lower magnetic permeability than electrical steel, so the gap contributes strongly to the magnetic reluctance of the motor. A smaller, controlled gap can improve magnetic coupling and reduce the current or magnet strength needed for a given air-gap field.
Why it cannot be eliminated
The rotor still needs mechanical clearance. Bearings, shaft deflection, thermal expansion, manufacturing variation, vibration, overspeed, and loads from the gearbox or wheels can all move parts away from their nominal positions. Too little clearance risks contact; too much can weaken coupling and increase losses or material requirements.
The gap may be cylindrical in a radial-flux motor or disc-shaped in an axial-flux motor. It may also vary intentionally around a salient rotor. Engineers control average gap, local variation, roundness, alignment, and surface features together.
“Air gap” describes the electromagnetic clearance inside the motor, not vehicle ground clearance and not a cooling duct, even when air or oil is present nearby.
For the construction trade-offs, see EV Motor Construction and Windings.