An EV power curve in the browser

/race runs a drivetrain model, not a throttle. Most browser demos fake the drive — a fixed acceleration shove that feels right. This one models the motor, because the motor is part of what the product is.

The curve every EV has

Electric drivetrains have a two-phase character:

v < v_base   F = T·G / r      traction-limited — flat torque
v > v_base   F = P / v        power-limited — pull fades with speed

Below base speed the limit is what the wheels can take — constant torque, constant acceleration. Above it the motor has no more watts to give, so force falls off as P/v. It's why EVs feel violent at launch and merely strong at highway speed.

The code

function driveAccel(v: number): number {
  return Math.min(LAUNCH_ACCEL, POWER_PER_MASS / Math.max(Math.abs(v), 0.5));
}

One line is the whole curve: min() of the two phases. The constants come from the vehicle class — a 1:10-scale racer runs ~1 kW on ~3 kg, which is ~330 W/kg. That number sounds wrong until you watch a real car in this class do a standing backflip off the throttle. Small electric vehicles are the most power-dense machines on wheels.

The honest ceiling

There is no top-speed clamp worth talking about — the clamp that matters is physical. Linear drag bleeds speed each frame (v̇ = −k·v), and with the drag constant tuned for the class, the car finds its own equilibrium at ~24 m/s ≈ 86 km/h: the speed where P/(m·v) exactly equals k·v. Top speed is a solution to an equation, not a constant in a config file.

That also means the demo degrades honestly — run onto grass and the drag constant triples; the car bogs down to a crawl for the same reason a real one would: the watts run out before the will does.