What is overdrive Is is the same as all-wheel drive?

Answer 1

Overdrive can refer to two different things. An overdrive is a device which was commonly used on rear-wheel drive automobiles to allow the choice of an extra-high overall gear ratio for high speed cruising, thus saving fuel, at the cost of less torque. It also refers to a combination of gearing inside a transmission or transaxle which results in the output speed being greater than the input speed. In the latter case, "overdrive" does not refer to a physically separate identifiable part/assembly. Four-wheel drive, 4WD, 4x4 ("four by four"), all-wheel drive, and AWD are terms used to describe a four-wheeled vehicle with a drivetrain that allows all four wheels to receive power from the engine simultaneously. While many people think exclusively of off-road vehicles, powering all four wheels provides better control on slick ice and is an important part of rally racing on mostly-paved roads. Four-wheel drive (4WD or 4x4 for short) was the original term, often used to describe truck-like vehicles that required the driver to manually switch between a two wheel drive mode for streets and a four-wheel drive mode for low traction conditions such as ice, mud, or loose gravel. The "all wheel drive" term (AWD for short) is just a marketing term. The AWD term is now being used to market both vehicles which continuously drive all four wheels and vehicles which switch from two wheel drive to four-wheel drive automatically as the primary drive wheels slip. The terms are thus quite vague in modern usage. The buyer must be wary. It is common for identical drivetrain systems to be marketed under different names for upmarket and downmarket branding, and also common for very different drivetrain systems to be marketed under the same name for brand uniformity. For example, Quattro, 4matic and 4motion can mean either an automatically engaging system with a Haldex clutch or a continuously operating system with a Torsen differential.