Chassis bracing may be the most under-rated and misunderstood modifications available to a vehicle. If the chassis accounts for the frame, steering, and suspension pick-up points; then this assembly must be as rigid as practical to perform at its best. Some compliance in the chassis helps dampen noise, vibration, and harshness (NVH), and it is not possible to completely eliminate flex. However, using strategic pick-up points, aftermarket chassis braces can be very effective at enhancing the feel of steering and suspension systems, greatly improving driver confidence and, as a byproduct, speed.
Bracing works by resisting the forces of compression and tension. Keeping two points at a fixed distance apart is the goal. With a rigid mounting between them, two points cannot bend toward each other. Judging a brace by its assembly* or how heavy it is may not be giving credit to the actual function of the part.
Braces are most commonly made out of steel or aluminum. These materials are inexpensive and strong. Aluminum has a lower weight, but fabricating it to be effective does carry a higher cost than a steel part. The most intricate parts of braces are the mounting points. Some manufacturers will, therefore, use steel for the mounting points and aluminum for the joining bar stock, and attach them with bolts. Carbon fiber and titanium are other materials chosen for their lightweight and strength, in the face of their expense.
Braces made out of one piece, or being a welded-up assembly, are assumed to be stronger than those made of multiple pieces. This statement is a risky one because it is taking design and quality out of the picture. A well-designed brace made with quality materials that bolts together would be preferable to a cheap, flexible brace made to be one-piece. It is generally true that brace which is installed as one piece would be more rigid, but unless the brace is then welded to the chassis itself, this point is largely irrelevant if the brace made is of high quality.
In general, bars mounted laterally (side-to-side) are effective at reducing twist in the chassis. Twisting movements cause the center points of the frame to move closer together. By fixing these points, the twist is resisted. Also, subframes and uni-bodies are made to accommodate the installation and mounting of other vehicle systems (exhausts, suspension parts, and drivetrain assembly) and closing these open areas “boxes” them in making the entire chassis stronger in that area. Lateral bracing will be felt more in turns where there is a high load.
Longitudinal braces help resist bending in the chassis as the front and rear traverse bumps in the road. The front and rear work together more than most would assume. By simply going over a bump, the chassis will bend, and in these bending moments, there is a numbness that reduces confidence. It’s not as apparent at road-speeds, but at highway or HPDE speeds, confidence is very important. Also, keeping the chassis flat reduces unwanted changes in wheelbase that can make the vehicle hard to set in turns after high-braking zones.