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Chassis Design: Principles and Analysis

Review of Chassis Design: Principles and Analysis
by "The Flying Lady"
The periodical of the Rolls-Royce Owners' Club (RROC/USA)

July/August 2002 issue

For the Rolls-Royce or Bentley enthusiast this important book has a very special place, for the vast majority of the material has been taken directly from the previously unpublished writings of Maurice Olley.

Born in Yorkshire England, Olley (1889-1972) grew up on the great Holyhead Road running through Wales. He describes his early impressions of a time when England was dominated by the steam engine. The idea of internal combustion took hold in France and Germany more quickly than in England, where it was first generally accepted as power for motorcycles. Still, young Olley developed a lifelong passion for the motorcar and had that goal firmly in mind during his educational years. His first real job out of school was working in France for Henry Royce, first as a tool designer. The remainder of his life was devoted to automobiles, first with Rolls-Royce both in England and in Springfield, MA, and finally with General Motors where he went on to be head of R & D at the Chevrolet Division. After his retirement in the early 1960s Olley wrote a series of monographs, covering his life's work in the field of chassis design.

By the late '60s the material was well on the way to publication when a very tight lid was suddenly placed on the project. The legal staff at GM, in view of the enormous litigation issues then raging around the "Corvair Affair" had decided it would be prudent to keep all suspension development information in-house and protected. We owe the authors of this new book a great debt of gratitude that finally, after more than thirty years under wraps, the Olley monographs have been released, and permission granted for their publication.

Keeping in mind the genesis-and also the purpose-of the book, it is best to think of it as a textbook. Olley wrote his notes for peers, for practicing engineers; he presupposes familiarity with principles and jargon. Almost every page is filled with geometric diagrams, illustrations, and mathematical progressions. Front and rear endpapers contain the symbols used throughout the work in developing the mathematical solutions. It is a true look into the world of automotive suspension design and despite the enormous body of data presented, the book is honest in its conclusion that even with all that has become understood and quantified, the subject remains probably the most complex field in automotive engineering. Even today, just as with new aviation products, much of the design effort in automotive suspensions can only be carried out during actual testing.

This work not only looks like a textbook, but one would expect that it will indeed be adopted for exactly that purpose. Any new student of automotive chassis design would do well to start his or her education with an appreciation and understanding of how suspension systems have reached their present development and I cannot imagine a better source than this single book. As the authors point out, today much of the mathematical effort, and even some of the qualitative understanding, can be sidestepped by solving chassis problems (suspension linkage for example) using one of the computer programs now available. But blind reliance upon a computer program can, and has, produced gross and expensive errors. I should think that the serious student of chassis design would insist upon first working his way through the graphical approach used by Maurice Olley, developed at a time when the only computer aid at his disposal consisted of the logarithmic scales on his slide rule.

And although the book is primarily aimed at engineers in industry and advanced-level users it is still recommended reading for the rest of us who neither aspire to a future in automotive engineering (some among us have long since developed a gentle but realistic appreciation of our personal limitations), nor wish to run through the mathematical equations just for the fun of it. It is perfectly legitimate to scan over the more difficult mathematics, accepting that they are correct as written, and instead focus one's attention on the diagrams/illustrations and the qualitative conclusions, each of which are skillfully explained.

Of particular value to the RROC reader is the sweeping nature of Olley's writing. He first started serious suspension experiments at GM in 1930, and includes all the early effort in his writing. During the mid-1920s a serious problem with front wheel shimmy had been studied by W. A. Robotham at Rolls-Royce using a bump rig. From about 1911 Rolls-Royce had always tested every chassis on a dynamometer by setting the rear wheels on 4-ft steel drums. Later the same idea was used for chassis fatigue testing by using an automobile engine to turn the drums, and this was the basis of the first bump rig. Maurice Olley took the idea with him to GM and began his own test program, seeking the solutions to front wheel shimmy and caster wobble. This was at a time when virtually all automobiles being produced used solid front axles and leaf springs. The eventual result of Olley's efforts was the development of the so-called flat-ride at GM and the adoption of independent front suspension in all GM products. The story of how that happened is explained in this book and it must be said that it was largely the effort of one man. I can still remember my grandfather raving about the ride of those first Cadillacs to benefit from the change: "It's like floating down the road, no matter whether you're sitting in front or back." Now at last I know how they achieved it and have also learned who was the driving force. Have you ever wondered why ifs is so superior to a fixed front axle? It is not just a matter of reducing the unsprung mass, as many believe. You will find answers to many questions you hadn't even imagined. The book contains 619 core pages and almost none of it is redundant. Starting with fundamental concepts the work then moves on to a consideration of a wide range of specific problem areas which are encountered in chassis design.

Throughout the book, the authors have included italic text to help the reader understand the concepts and to adjust for changes in modern SAE sign convention. Olley assumes an audience of engineers and does not explain such basic terms as "Ackermann angles." The authors' notes are particularly helpful in that regard and they include additional information at the end of each section as well as in appendix form. Even so, the non-technical reader may find a short review of basic engineering terms to be helpful. A bending load can visualized by a bar fixed at each end and loaded in the middle, a torsion load is a twisting force, a tension load is one that would tend to stretch a part, while a compression load will do the opposite. Stress, in engineering talk refers to the internal force in a member resulting from an external load and strain is the deformation of the material or structural member that the internal stress may cause. A force acting at right angles to an axis is called a normal force. These and other terms are used throughout the book and their exact meanings are essential to grasping the material.

One cannot come away from this book without gaining a greater appreciation of this complex subject. You will also come to have a great respect for Maurice Olley, one of the original pioneers in chassis design, and for the Millikens who carry on that tradition today (for more on the work of Milliken Research Associates go to where you will also find errata for this book posted). I, for one, have already decided to also order a copy of their SAE best-seller Race Car Vehicle Dynamics.

-James Pate

The Flying Lady
The periodical of the Rolls-Royce Owners' Club (USA)
* * *
Recipient of a 2001 Golden Quill and IAMC Silver Medal

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