A tire impact wrench is a specialized pneumatic or electric power tool designed for the specific task of installing and removing lug nuts on vehicle wheels. Its primary function is to deliver high levels of rotational torque in sudden, impactful bursts, making it capable of loosening fasteners that are extremely tight or corroded, which would be difficult or impossible to handle with a standard ratchet or breaker bar. The defining characteristic of a tire impact wrench is its internal impact mechanism. When resistance is encountered—such as when the socket contacts a tight lug nut—the tool does not stall. Instead, a rotating hammer inside the tool repeatedly strikes an anvil, transferring concussive rotational force to the output drive. This hammer-and-anvil action generates a series of high-torque impacts that shock the fastener loose without requiring the user to apply sustained physical force.

The power source for a tire impact wrench is a key differentiator. Pneumatic models, commonly called air impact wrenches, are powered by compressed air supplied from a shop compressor. They are known for their high power-to-weight ratio, durability, and consistent performance in professional automotive settings. An air-powered tire impact wrench requires a sufficient air compressor with adequate cubic feet per minute delivery to operate effectively. Cordless electric tire impact wrenches have advanced significantly, utilizing high-voltage lithium-ion battery packs. These battery-powered tools offer excellent portability and convenience, eliminating the need for an air hose, making them popular for mobile mechanics and roadside assistance. The torque output of a tire impact wrench is its most critical specification, typically measured in foot-pounds or Newton-meters. Professional-grade models can deliver substantial torque, often exceeding 1,000 ft-lbs of breakaway torque to remove stubborn lug nuts.

Using a tire impact wrench requires attention to technique and safety. The correct size impact socket must be used, as standard chrome sockets can shatter under the tool's intense force. The socket should be firmly seated on both the tool's drive and the lug nut. When removing a nut, the tire impact wrench should be held firmly, and the trigger squeezed to allow the impacts to work. It is common practice to use the tool to initially loosen the lug nuts before jacking up the vehicle to prevent the wheel from spinning. For installation, a torque-limiting feature or a separate torque wrench is essential. Running a tire impact wrench at full power to tighten lug nuts can dangerously over-torque them, leading to stretched studs or warped brake rotors. Many technicians use the tire impact wrench to snug the nuts and then finish tightening to the vehicle manufacturer's exact specification with a calibrated torque wrench. This combination of powerful impact mechanism and controlled application makes the tire impact wrench an indispensable tool for efficient and safe wheel service.