Today's cars, even the commuter ones, are designed and tested with tools and concepts that were unavailable even two short decades ago. But even with these advances, designing an automotive chassis is fraught with compromise, as numerous design parameters such as engine placement, cabin space, safety and material considerations and target costs play on what the final design will be. Few laymen or automotive enthusiasts will even care about understanding the forces - such as axial forces, shear forces, bending, torsion, angular deï¬?ection and moments of inertia - when they set out to purchase a car. Engineers worry about these things, but as we said, design compromises compel a lot of designs to be compromised in favor of balancing the features of a car towards a certain percentile of the population.
Car guys know that an automotive chassis' job is to hold the vehicle's components together while the car is in motion, all while being loaded by forces (such as vertical and lateral loads) that are transferred to it by the suspension, through the wheels. With standard OEM components like the tires, shocks, springs, bushings and a stock drivetrain, whatever loads are transferred to the chassis can be handled by the original design. The problem arises when you add stickier and/or wider tires, stiffer springs and/or shocks, stiffer bushings and more power. You then get unwanted chassis flex that affects the way your car handles. A big no no then. And when you talk about a car that's been on the road for more than a few years, you can add metal fatigue to the equation.
The best solution for a really stiff chassis would be a carbon fiber tub or a chassis that has been stitch-welded with a roll cage added. Highly impractical for a street/strip car enthusiast who has to juggle a budget or simply wants a good enough solution. Enter chassis braces. Old-timers will at once be intimately familiar with the simplest of these, the strut brace. This, even today, is one of the first add-ons you purchase when you put a chassis brace on your car. When cars were made with a separate ladder frame onto which the body was attached, there was also the subframe connector. Nowadays, you have strut braces for the front and rear, underchassis braces, fender braces, floorpan braces and rear suspension braces for stiffening the mounting points for the rear links.
Obviously, the effect of these braces will be to stiffen the chassis to the extent that tuning the car's handling will be a much more consistent affair. For those who take to the track, these chassis braces may not result in dramatic time improvements, but the improved confidence through better feel will improve consistency, which will affect the way the driver well, drives. This then, can indirectly lead to improved times. For less than new cars, these braces, as we have said, will stiffen the aging chassis to the extent that the platform will be as rigid, if not more, than when it was new.