A strut brace is a relatively simple device usually made of steel, carbon fibre or aluminium that bolts to the tops of the strut towers on a car. Strut braces can go in two places: across the engine bay or across the boot. Some vehicles come with strut braces from the factory, but this is primarily an aftermarket addition to a vehicle.
The primary benefit of a strut brace is the rigidity it provides to a chassis. During cornering, a tremendous amount of pressure is exerted on the chassis where the struts are mounted, which in turn can cause the chassis to flex a little. How much flex depends on the type of car. Some cars experience a lot of chassis flex while others may have hardly any. By tying the opposing strut towers together with a rigid brace, the chassis flex that occurs during cornering can be reduced or eliminated, resulting in a more rigid and responsive chassis and suspension.
More Precise Steering
Beyond making a chassis more rigid and less prone to flex, the other major benefit of a strut brace is it sharpens up steering response. During cornering, the steering feels more immediate and stable. This is why most strut braces are front strut braces and span the engine bay on a front-engine car or over the front boot on a rear-engine car like a Porsche 911.
The end purpose of a strut brace, like any other suspension improvement, is to improve the handling and driving characteristics of a vehicle, which in turn allows it to be driven more easily and confidently by the driver. It can also make a car more fun to drive, since the car feels more stable and has more immediate response.
Though the installation of a strut brace is ostensibly a performance upgrade, it could be argued that many people install a strut brace in their car to make it look more tuned or modified. Strut braces often feature a polished or chromed finish, which adds bit of brightness to an otherwise nondescript engine bay. They also can be made of carbon fibre, which adds a slick, high-tech look to the car. Strut bars are also sometimes painted or powdercoated to match the exterior colour of the vehicle.