Although frequently misunderstood and often misspelled, MacPherson struts are one of the most common suspension systems used on modern cars, found on everything from the Proton Savvy to the most formidable Porsche 911 Turbo. In this newly revised and updated installment of Ate Up With Motor, we’ll take a look at the origins and workings of the MacPherson strut, including modern variations like the Toyota Super Strut, GM HiPer Strut, and Ford RevoKnuckle.
Author’s note: This article has been extensively rewritten to clarify some points and correct certain factual errors. If you’re already familiar with the origins of the MacPherson strut (or really don’t care), skip ahead to page 2 for the technical nitty-gritty.
EARLE S. MACPHERSON
Earle Steel MacPherson (not Earl McPherson, as it is often misspelled in even reputable sources) was born in Highland Park, Illinois, a suburb of Chicago, on July 6, 1891. After earning a bachelor’s degree in mechanical engineering from the University of Illinois in 1915, he moved to the Detroit area and went to work for the Chalmers Motor Company.
MacPherson served in Europe during World War I, initially as a civilian engine mechanic for the Aviation Section of the U.S. Army Signal Corps (not a fighter pilot, as has sometimes been reported) and then as a captain in the American Expeditionary Forces’ aviation technical division. When the war ended, he returned to Detroit and took a job with the Liberty Motor Car Company. After Liberty was bought out by Columbia Motors in 1922, MacPherson left for Hupp, where he remained for about a decade, eventually becoming assistant chief engineer.
In 1934, with Hupmobile ailing badly, MacPherson and several other Hupp engineers (including future Hudson body engineer Carl Cenzer and future Nash engineer Ted Ulrich) departed for General Motors, where MacPherson became assistant to the vice president of engineering. One of their early projects was developing a prototype for a future small Chevrolet using Budd-patent unitized construction. Since the prototype was undertaken by the central engineering staff and not the division, we assume this was primarily a research project, but it became the basis of the 1935 Opel Olympia and the 1938 Vauxhall 10-4, GM’s first unit-body production cars.
Cenzer and Ulrich subsequently left for The Budd Company, where they continued working on unit body engineering, but MacPherson remained with GM. In May 1935, he was transferred to Chevrolet Division, reporting to then chief engineer James M. Crawford. MacPherson subsequently became Chevrolet’s chief engineer for passenger car and truck design.
THE CHEVROLET CADET
In the spring of 1945, Chevrolet general manager Marvin E. Coyle persuaded GM president Charlie Wilson to authorize the creation of a new Light Car Division and made MacPherson its chief engineer. The Light Car Division’s goal was to develop a cheaper, more economical compact car that Chevrolet dealers could sell alongside the standard Chevrolet.
Chevrolet’s Light Car project was prompted by Coyle’s fear that the imminent end of the war would bring another severe recession like the one that had paralyzed the auto industry shortly after the end of World War I (and nearly undone H.M. Leland’s fledgling Lincoln Motor Company, leading to its acquisition by Ford). However, Coyle was undoubtedly also aware that Ford was developing its own postwar Light Car, something that had been leaked to the press the previous summer and confirmed by Ford in July 1944. Since the small Ford was expected to undercut the price of a standard Ford (or Chevrolet) by a substantial and worrisome margin, it only made sense for Chevrolet to start working on a response.
The Light Car — subsequently christened Chevrolet Cadet — gave MacPherson a unique opportunity to develop a truly new design embodying his most advanced thinking. Some of the Cadet’s ideas were quite radical by contemporary American standards, including not only monocoque construction, but also hydraulic clutch actuation and an unusual centrally located manual transmission, connected to the clutch via a CV joint and a tubular driveshaft encased in a rigid steel tube. The engine, also all-new, was a lightweight OHV six with oversquare dimensions and dual flywheels, yielding 65 gross horsepower (48 kW) and 108 lb-ft (146 N-m) from 133 cu. in. (2,173 cc).
The Cadet was to be offered only as a four-door sedan, compact in exterior dimensions but boasting approximately the same interior room as a big Chevy of the mid-thirties. Target weight was only 2,200 lb (1,000 kg), about half a ton lighter than Chevrolet’s contemporary full-size cars, which contributed to excellent fuel economy. Despite its very modest curb weight, the Cadet also had decent handling and a surprisingly comfortable ride, thanks in large part to the Light Car’s most remarkable and controversial feature: fully independent suspension.
In the mid-forties, independent suspension was still a relatively new development in the United States. Independent front suspension had only become standard on big Chevrolets in 1941 and Ford wouldn’t offer it at all until the 1949 model year. Independent rear suspension was even less known outside of a handful of exotic European cars. Including it on a car intended to sell for less than $1,000 (about 10% less than a full-size Chevrolet) was a bold move and naturally made Chevrolet management very nervous.
The Cadet’s suspension, described in detail in MacPherson’s 1947 patent application, was the ancestor of his later strut design, although both layouts had other antecedents, including a 1929 patent filed by former FIAT managing director Guido Fornaca and William Stout’s 1935 Stout Scarab prototype. (Interestingly, the Fornaca patent, which as far as we know was never applied to a production car, is not cited in MacPherson’s 1947 application, but is among the references listed in his 1949 patent.)
Each of the Cadet’s wheels was suspended on a vertical strut that incorporated the wheel spindle and a coil spring wound around a tubular shock absorber (itself a novel feature at the time — contemporary GM cars still used lever-action dampers). Each front strut was located by a radius rod and two lateral links while each rear strut was located by a single trailing arm and a curious diagonal “swinging link” that connected the base of the strut to a point on the opposite side of the body, behind the rear axle line. The halfshafts, which had universal joints at both ends, did not contribute to wheel location.
MacPherson was a thoroughly methodical engineer and he was firmly convinced that this layout offered the best compromise between cost, packaging efficiency, handling, and ride. By most accounts, Cadet prototypes with this suspension worked very well, but the cost was problematic and the idea of GM’s cheapest U.S. model being more sophisticated than the priciest Cadillac probably sat ill in some quarters. MacPherson was obliged to develop a number of cheaper rigid-axle alternatives, if only to demonstrate the superiority of his fully independent setup. (One of these alternatives, incidentally, was a modified Hotchkiss drive layout with mono-leaf springs like those used on the later X-body Chevy II/Nova and first-generation Chevrolet Camaro/Pontiac Firebird.)
Had the Cadet been built as MacPherson wished, it would have been a landmark automobile, but by 1946, Chevrolet’s enthusiasm was fading rapidly. One reason was the departure of Marvin Coyle, whose promotion to group vice president in June 1946 left the project without a clear champion other than MacPherson himself. Another factor was the raw materials shortage that plagued all automakers in the immediate postwar years, a problem that forced a postponement of Cadet production plans that September and made the $1,000 target price — probably never very realistic to begin with — even more unlikely.
Moreover, the postwar recession Coyle feared had not materialized. Since civilian auto production resumed in late 1945, business had been booming. The real problem was not a lack of buyers, but a shortage of cars due to strikes and a scarcity of materials. The Chevrolet sales organization, which hadn’t had much voice in the Light Car project, saw no particular need for a smaller, cheaper car and balked at the idea of selling 300,000 of them a year, the minimum volume the corporation calculated Chevrolet would need to make any money on the Cadet.
GM senior management finally pulled the plug on the Light Car Division in May 1947, although MacPherson and a few of his team were transferred to the corporate Engineering staff to continue working on the Cadet as an advanced research project.
MACPHERSON AT FORD
The return to corporate Engineering was not a happy one for MacPherson, in large part because it meant once again working with his former boss, James Crawford, who had become corporate vice president of engineering two years earlier. Crawford and MacPherson had never seen eye to eye and their disagreements over the Cadet were particularly tense.
That situation soon came to the attention of Harold T. Youngren, who had been the chief engineer of Oldsmobile from 1933 to 1944 and had recently been appointed vice president of engineering at Ford Motor Company. At Youngren’s invitation, MacPherson left GM to become Ford’s executive engineer for design and development in September 1947. Without him, the Cadet project expired for good a year later.
When MacPherson arrived at Ford, the company’s own Light Car Division had already been canceled, but the car itself had caught the interest of Maurice Dollfus, head of Ford’s French subsidiary, who decided to buy the design, convert it to metric dimensions, and put it into production as the French Ford Vedette. We don’t know if MacPherson had any involvement in the engineering of the Vedette, which debuted about a year after his arrival at Ford, but if so, it was probably minor. (The Vedette did have independent front suspension, but contrary to many reports (and our own earlier error), it did not use struts.)
MacPherson would have the opportunity to apply some of his small car ideas to other products for Ford’s English and German subsidiaries, which in that era were still heavily dependent on the corporate headquarters in Dearborn for both engineering and styling. In January 1949, he applied for a patent (assigned to Ford) on what we would now recognize as the “classic” MacPherson strut suspension, described in further detail on the next page. This was in many respects a further refinement of the Cadet suspension, intended to minimize weight and production costs.
Later that year, the new suspension was incorporated into prototypes of the English Ford Consul, which in late 1950 would become the first production application. Unlike the Cadet, the Consul (and its six-cylinder sibling, the Ford Zephyr) did not have independent rear suspension, retaining cheaper Hotchkiss drive instead. Although MacPherson’s patent application noted that the strut design could easily be adapted for use at the rear wheels, Ford would not use rear struts on any production model until the arrival of the Mk3 Ford Escort in 1980.
MacPherson strut front suspension was subsequently applied to all of Ford’s English models and some iterations of the German Taunus. Curiously, Ford did not use struts on any U.S.-built models until the first Fox-platform Fairmont in 1978. Even early unitized Ford products like the 1958–1960 Lincoln and the original Ford Falcon retained double wishbones, although some of those cars used high-mounted springs (mounted atop the upper wishbone) that are sometimes incorrectly described as struts. Ford briefly contemplated using MacPherson struts for the front suspension of the 1958 Ford Thunderbird, but eventually opted not to because the potential cost savings were outweighed by the lack of commonality with other Ford models.
Other manufacturers were slow to adopt MacPherson struts, presumably due to the preexisting patents, but in 1957, Lotus Engineering’s Colin Chapman essayed a novel variation on MacPherson’s theme for the Lotus Type 12 race car. The so-called “Chapman strut,” used only at the rear wheels, employed the double-jointed halfshafts as control arms, supplemented by a trailing link on each side. Lotus also used Chapman struts on the Type 14 Elite from 1959 to 1962, but abandoned them on the later Elan for a more conventional rear strut layout.
The MacPherson strut was certainly Earle MacPherson’s most recognized contribution at Ford, but far from the only one. Others included working with supplier Thompson Products to develop front suspension ball joints suitable for full-size American cars (first adopted by Lincoln in 1952 and Ford and Mercury in 1954) and pushing for the adoption of monocoque construction for the 1958 Thunderbird and Lincoln. MacPherson could be sharp-tempered and, like many determinedly rational people, had little patience for anything he viewed as frivolous, but his engineering talents were considerable.
MacPherson was promoted from executive engineer to chief engineer in 1949. In May 1952, he succeeded Harold Youngren as Ford’s vice president of engineering. Health problems and approaching retirement age prompted MacPherson to step down from that role in April 1957, succeeded by Andrew Kucher, but he remained with Ford for another year as vice president and engineering policy adviser. MacPherson died in 1960 at the age of 69.
A few years later, as MacPherson’s original patents expired, MacPherson strut suspensions began a rapid proliferation in the U.K., Europe, and Japan. Struts took longer to catch on among other Detroit automakers, particularly for their U.S.-built offerings, but today, there are very few automakers anywhere that don’t use MacPherson struts for at least some models — even companies like Honda, which had long eschewed struts in favor of double wishbones.