Engine braking happens when a rider closes the throttle and the engine resists the rotation of the rear wheel through the drivetrain. In MotoGP, this effect is powerful because the engines have high compression, low rotating mass, and very direct mechanical connections. Used well, engine braking helps slow the bike and load the front tire as the rider enters a corner.
Used poorly, it can make the rear wheel hop, slide, or lose stability.
Key Facts
- Engine braking torque is a negative torque at the rear wheel when the closed throttle engine resists wheel rotation.
- Wheel torque from the engine is approximately T_wheel = T_engine x gear ratio x final drive ratio.
- Rear wheel power during engine braking is P = T x omega, where T is negative and omega is wheel angular speed.
- Rear slip ratio can be estimated as slip = (v_bike - v_wheel) / v_bike during deceleration.
- MotoGP engine braking control adjusts throttle butterflies, fuel, ignition, and sometimes clutch behavior to tune negative torque.
- A slipper clutch reduces back torque mechanically so the rear wheel is less likely to hop during aggressive downshifts.
Vocabulary
- Engine braking
- Engine braking is the slowing force produced when a closed throttle engine resists the rotation of the driven wheel.
- Back torque
- Back torque is the reverse torque sent from the rear wheel through the drivetrain into the engine during deceleration.
- Slip ratio
- Slip ratio compares wheel speed with bike speed to describe how much the tire is sliding or being overdriven.
- Slipper clutch
- A slipper clutch is a clutch mechanism that partially disengages under strong back torque to prevent rear wheel hop.
- Ride-by-wire
- Ride-by-wire is an electronic throttle system where sensors and a control unit command throttle opening instead of a direct cable.
Common Mistakes to Avoid
- Treating engine braking as the same as the rear brake is wrong because engine braking comes through the drivetrain and changes with gear, rpm, throttle position, and electronic control.
- Assuming more engine braking always means faster corner entry is wrong because too much negative torque can overload the rear tire and reduce stability.
- Ignoring the effect of downshifting is wrong because a lower gear increases torque multiplication and can sharply increase back torque at the rear wheel.
- Thinking electronics only reduce engine power is wrong because MotoGP control systems also shape deceleration torque by adjusting throttle, ignition, fuel, and clutch related behavior.
Practice Questions
- 1 A MotoGP engine produces -18 N m of braking torque at the crank. The selected gear ratio is 2.0 and the final drive ratio is 2.8. Ignoring losses, what braking torque reaches the rear wheel?
- 2 A bike enters a braking zone at 70 m/s. During deceleration the rear wheel speed corresponds to 66.5 m/s. Using slip = (v_bike - v_wheel) / v_bike, calculate the rear slip ratio as a decimal and as a percent.
- 3 A rider complains that the rear wheel chatters when downshifting into a corner. Explain how reducing engine braking electronically or using a slipper clutch can improve stability.