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The Largest Independent Automotive Research Resource
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"Why It's Good"

Chassis Rigidity

By Carey Russ

In reading tests of and articles about new cars in newspapers and magazines and on The Auto Channel, you may have seen much attention paid to increased chassis rigidity in new vehicles. We on the writing-about-it side certainly hear much on the subject, at press conferences and new car introductions and in the informational material given to us by the auto manufacturers. "The all-new 1998 Bloxfire GT is 75% more rigid than the 1997 model" is a typical sort of statement. "What ever does that mean and is it important?," you may wonder.

It certainly is important. The chassis of a car (or truck, or any other sort of wheeled vehicle) is the most important structural part. The more rigid it is, the better chance that all of the wheels will point in the desired direction. This is a Good Thing for control, safety, and comfort.

Consider control, primarily steering response and cornering ability. If the vehicle's frame flexes too much, the wheels, and therefore the vehicle itself, will move in directions other than the one which the driver intended. Not a Good Thing. This movement doesn't have to be large to be noticeable. The need for constant steering corrections while driving may be due to frame flex (among many other possible causes.) This can be tiring at best (a definite safety factor), and can make a car's cornering abilities less than optimum - another very negative safety factor. In the "good olde days" when automobile frames were less rigid than today, sports cars often had very stiff suspensions. This reduced unwanted wheel movement. It also reduced comfort, and, seemingly paradoxically, sometimes reduced handling abilities as well. No paradox, really. The tires must be in contact with the ground in order to transmit acceleration, braking, or cornering forces. A too-stiff suspension will have wheels rebounding into the air, where the tires do nothing.

Another noticeable effect of flex is noise. As different parts of a vehicle move with respect to each other, noise results. With time, things loosen and get even more annoying noisy. Squeaks and rattles are the most noticeable effects, but constant flex or vibration can break things, too. Not good, for cosmetic, comfort, or possibly (depending on what breaks) safety reasons.

So the modern, more rigid car is quieter, more comfortable, handles better, and is safer than its flexy forebear. Why did it take the automotive industry so long to figure this out?

Knowledge increases over time. The automobile as we know it is barely over 100 years old, and depends on quite a few other technologies as well. There has been a certain amount of mechanical natural selection over the past century, with plenty of evolutionary dead ends and side tracks along the way. Many modern materials, construction techniques, and auxiliary technologies used in automobile manufacture today are considerably newer than that century, too. Karl Benz and Henry Ford didn't have the fruits of modern metallurgy, heavy-duty machine tools, space-age composite materials, or computers. They barely had electricity. Industry pioneers adapted horse-drawn wagon and bicycle technology to the automobile, but the automobile is a different sort of machine than either of those. It took time to learn, and they're still learning.