The sub frame is a structural part of the car's chassis that sits within the larger frame of the chassis and can accommodate the engine, transmission and steering components and acts as a base to fix the suspension to the vehicle.
A sub frame helps to reinforce the chassis and is usually made of thick steel tubing or panels which are spot welded or welded together and bolted or welded onto the car. Modern front wheel drive vehicles have a separate front and rear sub frame, which helps to spread the weight of the vehicle evenly, improving the overall handling of the vehicle on the road.
The main function of the sub frame is to assist the chassis in helping to take some of the strain, and balance the load of the vehicle. The sub frame is also responsible for absorbing and dampening some of the vibrations produced by the engine and, if fixed with springs or rubber bushings, they can also help to absorb some of the noise. The sub frame also functions to absorb some of the impact of a collision, helping to distribute the force of the impact across the entire car which results in minimising the impact experienced by the occupants of the car in a crash.
Sub frames can become misaligned which can affect the suspension and steering and cause the vehicle to vibrate when in motion. Often the cost to rebuild and realign an old or damaged sub frame far exceeds the cost of buying a new one. Whether you need a new sub frame because you are embarking on a project to build your own car, or the current sub frame needs replacing because of damage received in an accident, or it's suffering from old age with the metal tired and rusted, buying a sub frame will ensure you get the perfect component for the car make and model you require.