reverse gear

Reverse gear is a transmission setting that inverts the direction of output shaft rotation relative to engine rotation, propelling a vehicle backward. In manual transmissions, it is typically an idler gear meshed between the main shaft and layshaft, or a separate gear pair that reverses the rotational sense. In automatic transmissions, planetary gear sets and clutch packs are reconfigured hydraulically to produce backward motion. The symbol R appears on shift gates and displays to indicate this position.

The mechanical action differs between transmission types. Manual reverse gearboxes often use a sliding gear or fork mechanism to engage a dedicated reverse idler; this idler does not mesh during forward driving, which is why reverse often requires a pause or deliberate action to select. Automatics achieve reversal through hydraulic pressure routing, without physical gear sliding. In electric vehicles, reverse is accomplished by reversing the polarity or direction of motor current, requiring no mechanical gear at all.

Gear ratios in reverse are typically numerically similar to first gear, ranging from 3.5:1 to 4.5:1 in passenger vehicles, giving adequate torque multiplication for moving heavy loads at low speed. Trucks and commercial vehicles may have deeper reverse ratios to assist with trailer work and tight-space maneuvering. The ratio is fixed once designed; there is no adjustment in service.

Engagement damage is common when drivers shift into reverse while the vehicle is moving forward, or when they select it harshly at high idle speed. This causes gear teeth to strike and wear prematurely, and can fracture teeth or shear synchronizer rings in synchronized transmissions. Proper procedure requires the vehicle to be fully stopped before engaging reverse, and gentle throttle application once engaged.

The reverse idler gear in manual boxes typically rotates on a fixed shaft perpendicular to the main and layshafts, and its teeth face the gears on both shafts. Wear on this single point of contact is cumulative; a worn idler permits the driven gear to shift laterally, causing noise and potential disengagement. Replacement requires partial transmission disassembly but is a standard repair procedure.

Reverse is also used strategically in heavy machinery and forklifts to increase effective working range without turning the vehicle. In forklifts, reverse provides an independent power path, and reverse-only vehicles exist for specialist load handling. The naming reflects direction: the gear setting itself does not move backward, but causes the vehicle to do so.