Tuning the lift-off torque map
Calibration engineers shape a curve of regen torque against pedal position and speed — not a single number.
- Explain tuning the lift-off torque map at engineering level
- Read the numbers that define the behaviour
- Apply the idea to a real braking system
Overview
One-pedal driving feel comes from a two-dimensional torque map: how much regen torque is commanded for a given accelerator pedal position, at a given road speed. Getting this map right is one of the most iterated calibration tasks in an EV programme.
In depth
Torque Calculator
Torque available at the shaft and at the wheel for a given power.
T (Nm) = P (kW) × 9550 ÷ n (rpm) ; T_wheel = T × gear ratioTorque is the inverse of the power equation. A single-speed reduction gear multiplies motor torque by its ratio while dividing speed by the same factor.
Example: 150 kW at 4,500 rpm → 318 Nm at the shaft; through a 9:1 reduction that is 2,865 Nm at the wheels.
- Wheel torque divided by rolling radius gives tractive force in newtons.
- Traction, not motor torque, usually limits launch acceleration.
- Gear losses of 2–4% should be subtracted from wheel torque.
The shape of a good map
A well-tuned map keeps deceleration roughly constant for a given pedal position across a wide speed range, even though the raw torque needed to produce that deceleration changes with speed — drivers judge the feel by deceleration, not by torque. The map also needs a smooth, predictable ramp-in so lifting off gently doesn't feel like hitting a wall.
| Single fixed level | Adaptive / driver-selectable | |
|---|---|---|
| Simplicity | Very simple | More complex to validate |
| Driver satisfaction | Polarising | Broader appeal |
| Energy recovery | Fixed | Driver can maximise it |
Some manufacturers put regen-level selection on steering wheel paddles, letting the driver dial in strength moment to moment rather than through a fixed drive mode.
Key takeaways
- Lift-off torque is calibrated as a map against both pedal position and speed, not a fixed number.
- Good calibration targets constant perceived deceleration, not constant torque.
- Adaptive or driver-selectable regen strength broadens appeal without changing hardware.
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