underdrive
Slower output ratio
Underdrive refers to a gear ratio or pulley system that reduces output speed relative to input speed, the opposite of overdrive.
In automotive contexts, an underdrive pulley slows engine accessories like the alternator and water pump, reducing parasitic drag to free up horsepower: He installed underdrive pulleys on his Mustang.
The term also applies to transmissions where lower gears multiply torque at reduced speeds.
Making something smaller
- gear ratioTeeth count relationship
- transmissionSending of information
- drivetrainVehicle power transmission system
- low gearTransmission's torque-maximizing position
differential · off-road · rock crawling · towing · hill climbing · granny gear · transfer case · powertrain
Vehicle efficiency rating
- energy savingsReduced power consumption
- engine efficiencyMotor's energy conversion rate
- mechanical advantageForce output over input
Looped automotive accessory drive
- alternatorMechanical-to-electrical energy converter
- power steeringAssisted vehicle directional control
- water pumpDevice circulating liquid mechanically
- bolt-onAttached by fastener
engine bay · throttle response · street performance · drag racing
reduction
Making something smaller
- gear ratioTeeth count relationship
- transmissionSending of information
- drivetrainVehicle power transmission system
low gear · differential · off-road · rock crawling · towing · hill climbing · granny gear · transfer case · powertrain
fuel economy
Vehicle efficiency rating
- energy savingsReduced power consumption
- engine efficiencyMotor's energy conversion rate
- mechanical advantageForce output over input
serpentine belt
Looped automotive accessory drive
- alternatorMechanical-to-electrical energy converter
- power steeringAssisted vehicle directional control
- water pumpDevice circulating liquid mechanically
bolt-on · engine bay · throttle response · street performance · drag racing
underdriveoverdrive
Efficiency mode at speed
overexertion · maximum effort · full throttle · going all out · overperformance