The MacPherson Strut

CONCLUSION

The evolution of the MacPherson strut has been comparable to that of other automotive innovations like automatic transmission, which has also seen many changes and innumerable additions and modifications intended to minimize its weaknesses without sacrificing its basic selling points.

As with automatic, some of the MacPherson strut’s variations have caught on while others have not, but the layout’s virtues are still compelling enough to make it ubiquitous, if not quite universal. We have no doubt that Earle MacPherson’s strut suspension will remain in common use long after his name is forgotten. Many people have already forgotten how to spell it!

# # #

ACKNOWLEDGMENTS

The author would like to thank Jamie Myler of Ford Archives for providing archival images of Earle MacPherson, the Ford Consul, and RevoKnuckle (as well as a copy of Ford’s 1957 press bio of MacPherson); Kathy Adelson of GM Media Archives for her help in locating archival images of the Chevrolet Cadet and the HiPer Strut diagrams; and Kris Carter of the Celica GT-Four Drivers Club for the use of his Super Strut photos.


NOTES ON SOURCES

Our sources on the life of Earle MacPherson, the origins of the Chevrolet Cadet, and the origins of the MacPherson strut suspension included Herb Adams, Chassis Engineering (HP1055) (New York: HPBooks, 1993); the Auto Editors of Consumer Guide, Cars That Never Were: The Prototypes (Skokie, IL: Publications International, 1981); and “1951-1956 Ford Consul and Zephyr,” HowStuffWorks.com, 11 October 2007, auto.howstuffworks. com/ 1951-1956-ford-consul-zephyr.htm, last accessed 25 June 2014; Griffith Borgeson, “How Leland Lost Lincoln to Ford: The little-known battle of two Henry’s: dedication to an ideal vs. big business,” Motor Trend Vol. 19, No. 2 (February 1967): 58–62, 82–83; “British Fords Get U.S. Look,” Popular Science Vol. 158, No. 3 (March 1951): 150–151; David A. Crolla, ed., Automotive Engineering: Powertrain, Chassis System and Vehicle Body (Burlington, MA: Butterworth-Heinemann/Elsevier, 2009); “Editor’s Note: Earl S. MacPherson and His Invention” [the article whose errors prompted the original version of this article], VW Trends 23 April 2003, www.vwtrendsweb. com/features/ 0306vwt_macpherson_strut_suspension/, last accessed 27 June 2014; Craig Fitzgerald, “Earl S. MacPherson” [note that he too misspells MacPherson’s name!], Hemmings Sports & Exotic Car #3 (November 2005); “Ford,” Autodriver Vol. 57 (1957): 93; Ford Motor Company, Annual Report, 1957, and “MacPherson, Earle S. – Biography” [press release], 26 April 1957; Ford-Werke A.G. Köln, “Taunus 17M” [German brochure 9 P 115/2], 1957; Ken Gross, “Stovebolt Six with an Aussie Accent: 1948 Holden,” Special Interest Autos #49 (February 1979), pp. 26-33, 62; “Icons: Earle MacPherson,” Motor Trend Vol. 58, No. 3 (March 2006); Michael Lamm, “The Imagineer William B. Stout: Automobile and Airplane, His Goal Was to See Them Wedded,” Car Life Vol. 14, No. 7 (August 1967): 54–58; David L. Lewis, “Ford’s Postwar Light Car,” Special Interest Autos #13 (October-November 1972): 22–27, 57; and “Lincoln Cosmopolitan: The Gleam in Edsel Ford’s Eye,” Car Classics April 1973, reprinted in Lincoln Gold Portfolio 1949-1960, ed. R.M. Clarke (Cobham, England: Brooklands Books Ltd., ca. 1990): 5–17; Karl Ludvigsen, “The Truth About Chevy’s Cashiered Cadet,” Special Interest Autos #20 (January-February 1974), pp. 16–19; Mike McCarthy, “Honda’s Headliners,” Wheels August 1985: 38–43; “Necrology,” Automotive Industries Vol. 122 (1960): 53; “News,” Motor Truck News Vol. 47 (1958): 91; news, SAE Journal Vol. 34 (1934): 71; Jan Norbye, “Half-Hour History of Unit Bodies,” Special Interest Autos #18 (August-October 1973): 24–29, 54; “Personals,” Iron Age Vol. 160 (1947): 104; “Personals,” Iron Age Vol. 164 (1949): 43; personnel news, Electro-Technology Vol. 33, No. 3 (1944): 234; Don Sherman, “Volvo 242GL,” Car and Driver Vol. 20, No. 7 (January 1975); William K. Toboldt and Larry Johnson, Goodheart-Willcox Automotive Encyclopedia (South Holland, IL: The Goodheart-Willcox Company, Inc., 1975); the Suspensions section of Mark Wan’s excellent AutoZine Technical School (1997–2011, www.autozine. org/ technical_school/ suspension/ Index.html); Mary Wilkins and Franck Hill, American Business Abroad: Ford on Six Continents (Detroit: Wayne State University Press, 1964); and of course MacPherson’s patents: Earle S. MacPherson, assignor to General Motors, “Vehicle Wheel Suspension System,” U.S. Patent No. 2,624,592, filed 21 March 21 1947 and issued 6 January 1953; and Earle S. MacPherson, assignor to Ford Motor Company, “Wheel Suspension for Motor Vehicles,” U.S. Patent No. 2,660,449, filed 27 January 1949 and issued 24 November 1953.

Some information of the many variations on the theme included Sam Abuelsamid, “Quick Spin: 2010 Buick LaCrosse CXS gets HiPer,” Autoblog, 25 March 2010, www.autoblog. com, accessed 23 June 2015; Ian Adcock, “Renault Megane 265 Trophy,” Road & Track 20 January 2012, www.roadandtrack. com, accessed 12 July 2014; James M. Amenda, “GM’s HiPer Strut Rethinks MacPherson Suspension,” Wards Auto, 30 March 2010, wardsauto. com, accessed 17 July 2014; Ben Barry, “Ford Focus RS (2009) CAR test review,” CAR 22 February 2009, www.carmagazine. co.uk, accessed 12 July 2014; Patrick Bedard, “BMW 733i,” Car and Driver Vol. 23, No. 10 (April 1978), reprinted in BMW 7 Series Performance Portfolio 1977–1986, ed. R.M. Clarke (Cobham, England: Brooklands Books Ltd., ca. 1999): 29–33, 48; “BMW’s new big ones,” Autocar 28 May 1977, reprinted in BMW 7 Series Performance Portfolio 1977–1986: 5–9; “Brief Test: Peugeot 205 CTI,” Motor 2 August 1986: 46–49; Kris Carter, “Changing 205 Super Strut Suspension,” Icy Designs, March 2010, diy.icydesigns. com/ article/ 93/Toyota/ Celica/ 1994-99_(ST20x)/ Suspension/Brakes/ Steering/ Changing_205_Super_Strut_Suspension/, accessed 10 July 2014; Yung Chang Chen, Po Yi Tsai, and I An Lai, “Kinematic Analysis of Roll Motion for a Strut/SLA Suspension System,” World Academy of Science, Engineering and Technology Vol. 6, No. 5 (2012): 1172–1176; K.C. Colwell, “Ford RevoKnuckle and GM HiPer Strut Explained,” Car and Driver Vol. 56, No. 9 (March 2011), www.caranddriver. com, accessed 12 July 2014; Csaba Csere, “F-Tech,” Car and Driver Vol. 27, No. 7 (January 1982): 46–48; Richard Doig, “ST205 Superstrut Suspension,” New Zealand GT-Four Homepage, 2007, gtfour.supras. org.nz/ superstrut.htm, accessed 8 July 2014; Dan Edmunds, “Straight Line: 2010 Buick LaCrosse CXS: Hiper [sic] Strut Suspension Walkaround,” Inside Line, 2 April 2010, blogs.insideline. com/ straightline/, accessed 23 June 2015; ‘elansprint71,’ Roger French, and Peter Ross, “The ‘Chapman’ strut,” LotusElan.net, 16 November 2011 to 11 February 2012, www.lotuselan. net/ forums/ lotus-suspension-f42/ the-chapman-strut-t24055.html, accessed 24 June 2015; Ford Motor Company, “New Ford Focus RS: A Legend Returns” [press release], 4 July 2008; “Ford’s happy event,” Autocar 17 July 1976: 12–21; General Motors, “Buick LaCrosse’s Innovative HiPer Strut Suspension Delivers Improved Ride and Handling” [press release], 24 March 2010; Akira Higuchi, assignor to Toyota Jidosha Kabushiki Kaisha, “Suspension of Vehicle,” U.S. Patent No. 4,844,505, filed 14 December 1987 and issued 4 July 1989; “Kingpin Inclination, Caster, etc. for MacPherson Strut” [forum discussion], Eng-Tips, 20 January – 24 January 2005, www.eng-tips. com/ viewthread.cfm?qid=113181, accessed 27 July 2014; Randy Leffingwell, Mustang: America’s Classic Pony Car (Ann Arbor, MI: Lowe & B. Hould Pub., 1999); A.K. Legg, Peugeot 205 Owners Workshop Manual 1983 to 1985 (Sparkford Nr Yeovil, Somerset: Haynes Publishing Group, 1986); “Lotus Elite / Lotus Type 14,” Unique Cars and Parts, n.d., www.uniquecarsandparts. com.au, accessed 24 June 2014; Wolfgang Matschinsky, assignor to Bayerische Motoren Werke Aktiengesellschaft [BMW A.G.], “Independent Suspension of a Steered Wheel of a Motor Vehicle,” U.S. Patent No. 4,145,072, filed 30 March 1977 and issued 20 March 1979; John Miles, “More than Skin Deep,” Autocar 20 June 1981, reprinted in BMW 5 Series Gold Portfolio 1981–1987, ed. R.M. Clarke (Cobham, England: Brooklands Books Ltd., ca. 1993): 5–8; Chuck Nerpel, “Driving Impression: BMW 733i,” Motor Trend Vol. 30, No. 4 (April 1978), reprinted in BMW 7 Series Performance Portfolio 1977–1986: 26–29; new car price guide, 5 November 1993, Car and Driver (Japan Edition) 10 December 1993: 220–230; Yasushi Nishikiuma et al, assignors to Toyota Jidosha Kabushiki Kaisha, “Suspension for Steerable Driving Wheel in Vehicle,” U.S. Patent No. 5,048,859, applied 30 May 1990 and issued 17 September 1991; David Phipps, “The Lotus Elite,” Profile Publications #48 (1967); “Renault Mégane RenaultSport Review,” Autocar, n.d., www.autocar. co.uk, accessed 12 July 2014; “Renaultsport Megane 250 gallery,” Evo October 2009, www.evo. co.uk, accessed 16 July 2014; “Road Test: Peugeot 205 GTI,” Motor 26 May 1984: 20–23; Toshiyasu Santo, assignor to Toyota Jidosha Kabushiki Kaisha, “Strut Type Suspension,” U.S. Patent No. 4,995,633, filed 31 August 1989 and issued 26 February 1991; Don Sherman, “Ford Fairmont: Ford builds a Volvo, and it works,” Car and Driver Vol. 23, No. 3 (September 1977): 27–34; Showtime4U, “Toyota trueno & levin AE101 introduction year 1991,” YouTube, [disabled video], uploaded 24 February 2014, accessed 27 July 2014; “Super Strut Suspension,” Toyota Corolla FX GT, 2009, www.oocities. org/fxgt20/ superstrut.htm, accessed 26 July 2014; “Super Strut Suspension” and “205 Suspension,” Celica GT-Four Drivers Club, 2013, www.gtfours. co.uk/ what/ sstrut/ sstrut.htm and www.gtfours. co.uk/ pics/ suspension/ 205/sus.htm, accessed 10 July 2014; “Superstrut Suspension, ST202 – ST 205 suspention [sic],” 6G Celicas Forums, 18 August 2005 – 13 July 2014, www.6gc. net/ forums/ index.php?showtopic=28093, accessed 27 July 2014; Toyota Motor Corporation, 75 Years of Toyota: Vehicle Lineage, www.toyota-global. com, accessed last accessed 15 April 2014; Toyota Motor Sales, “Celica” [CD0016-9909], September 1999; “Corolla Levin” [Japanese brochure CE0047-9106], June 1991; and “Corolla Levin” [Japanese brochure CE0022-9505], May 1995; Ron Wakefield, “Ford Fiesta: Henry builds a minicar,” Road & Track Vol. 28, No. 2 (October 1976): 34–36; Jeremy Walton, Escort Mk 1, 2 & 3: The Development & Competition History (Sparkford, Somerset: Haynes Publishing Group, 1985); Mark Wan, “Focus RS,” AutoZine, 4 June 2009, www.autozine. org/ Archive/ Ford/old/ Focus_Mk2.html#RS, accessed 16 July 2014; “Megane RS (Renault Sport),” AutoZine, 23 November 2009, www.autozine. org/ Archive/ Renault/new/ Megane_III.html, last accessed 12 July 2014; “Opel Astra,” AutoZine, 18 June 2012, www.autozine. org/ Archive/ Opel/new/ Astra_2009.html, last accessed 12 July 2014; “Opel Insignia/Buick Regal,” AutoZine, 27 November 2011, www.autozine. org/ Archive/ Opel/new/ Insignia.html, last accessed 12 July 2014; and “Renault Megane,” AutoZine, 22 December 2006, www.autozine. org/ Archive/ Renault/old/ Megane_II.html, last accessed 12 July 2014; and xreknil, “Toyota superstrutsuspension [sic],” YouTube, https://youtu.be/c9tj43J8cJk, uploaded 12 June 2012, accessed 27 July 2014.

Additional background sources included the Auto Editors of Consumer Guide, Encyclopedia of American Cars: Over 65 Years of Automotive History (Lincolnwood, IL: Publications International, 1996); Bob Bolles, “Camber Crutches,” Circle Track 18 June 2004, www.circletrack. com, accessed 17 July 2014, and “Understanding and Learning Caster and Camber Settings,” Circle Track 2 April 2013, www.circletrack. com, accessed 17 July 2014; John R. Bond, “Porsche 901,” Road & Track Vol. 15, No. 4 (December 1963): 24–26; Gérard Bordenave, “Ford of Europe, 1967-2003,” Cahiers du GRES [Groupement de Recherches Economiques et Sociales, Université Monteqsquie-Bordeaux and Université des Sciences Sociales Tolouse], Cahier No. 2003-11 (September 2003); Carl Breer and Anthony J. Yanik, The Birth of Chrysler Corporation and Its Engineering Legacy, Second Edition (Warrendale, PA: Society of Automotive Engineers, Inc., 1960); Douglas Brinkley, Wheels for the World: Henry Ford, His Company, and a Century of Progress (New York: Viking Penguin, 2003); Arch Brown, “Chrysler’s Magnificent Mistake: 1934 Airflow ‘CU,'” Cars & Parts August 1992: 22–26; and “1935 Plymouth: ‘A New Picture of Car Value,'” Special Interest Autos #172 (July-August 1999), reprinted in The Hemmings Book of Plymouths: driveReports from Special Interest Autos magazine, eds. Terry Ehrich and Richard Lentinello (Bennington, VT: Hemmings Motor News, 2002): 14–21; Arch Brown, Richard Langworth, and the Auto Editors of Consumer Guide, Great Cars of the 20th Century (Lincolnwood, IL: Publications International, Ltd., 1998); Darren Burnhill, “How Caster Angle Affects Camber Angle,” RC Tek, 2009, www.rctek. com, accessed 17 July 2014; Bill Carroll, “Inside Pontiac’s Terrific Tempest!” Sports Cars Illustrated October 1960, reprinted in Car and Driver on Pontiac 1961–1975, ed. R.M. Clarke (Cobham, England: Brooklands Books Ltd., ca. 1985): 5–7, 16; Floyd Clymer, Floyd Clymer’s Independent Test Report and Investigation of 1949 Ford Cars (Los Angeles: Floyd Clymer, 1948); John A. Conde, “Rare Pair: Twin 1948 Nash Convertibles,” Special Interest Autos #37, (November-December 1976): 34–39, 64–65; Mike Covello, ed., Standard Catalog of Imported Cars 1946–2002, Second Edition (Iola, WI: Krause Publications, 2001); “Engineering the Camaro,” Car Craft January 1968, reprinted in Camaro Muscle Portfolio 1967–1973, ed. R.M. Clarke (Cobham, England: Brooklands Books Ltd., ca. 1992): 43–46; Edward Eves, “Designs Analyzed-8: Alfa Romeo Giulia GTV,” Autocar 21 December 1967, reprinted in Alfa Romeo Giulia Coupes Gold Portfolio 1963–1976, ed. R.M. Clarke (Cobham, England: Brooklands Books Ltd., ca. 1992): 68–71; Joe Fabrini, “Opel Olympia,” Better Parts Ltd., 7 July 2013, betterparts. org, accessed 28 July 2014; Jim and Cheryl Farrell, Ford Design Department: Concepts and Showcars 1932–1961 (Roseburg, OR: Jim and Cheryl Farrell, 1999); Guido Fornaca, “Wheel-Suspension Means for Motor Vehicles,” U.S. Patent No. 1,711,881, filed 13 July 1927, issued 7 May 1929; Edwin Storm’s Free Car Brochures website at the Old Car Manual Project (storm.oldcarmanualproject. com); David Halberstam, The Reckoning (New York: William Morrow and Company, 1986); Maurice D. Hendry and Dave Holls, Cadillac: Standard of the World: The Complete History, Fourth Edition (Princeton, N.J.: Automobile Quarterly, 1990); Tim Howley, “Full Dress Falcon 1963 Sprint V-8,” Special Interest Autos #67 (January-February 1982), The Hemmings Motor News Book of Postwar Fords: driveReports from Special Interest Autos magazine, eds. 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38 Comments

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  1. You can still get some camber change out of a strut.

    Looking at your diagram, when the suspension compresses, the lower control arm will move through an arc that will push the bottom of the knuckle outward.

    The bottom of the strut can’t rotate relative to the knuckle, so its upper mount will have to flex some to accommodate the change in angle.

    Nitpicking aside, it’s always cool to learn the story behind an eponym. When can we learn about Mr Cardan and his double-joint?

    1. MacPherson struts do have some camber change in compression, as do most independent suspensions other than pure trailing arms, but the amount is very small because the effective swing-arm length is quite long. What they don’t provide is camber [i]gain[/i] with body roll, the way a double-wishbone suspension or swing-arm suspension does. As the body leans and the outside spring compresses, the arc of the lower control arm does push the lower edge of the spindle outward (which would tend to create negative camber), but the magnitude of that force is much less than that exerted by the strut as body lean pushes it outward (which tends to create positive camber). The result is always a net camber loss.

      The fact that increasing positive camber is called camber loss and creating negative camber is called camber gain is the kind of thing that gives me a headache.

      Gerolamo Cardano didn’t actually create the DCJ, since he died in the 16th century — the universal joint was named after him because he invented the concept, but the double Cardan joint was a refinement developed many years after his death. He was an interesting guy, though…he and André Citroën would have gotten along well.

  2. Hmmm…true. Suspensions are funny because major differences in ride, handling and character are wrung from tiny geometry tweaks. Through much engineering education, differences in angle that we’re talking about would all be considered “vertical” to a reasonable approximation.

    The funny part about a double-cardan joint is that when there’s there’s one u-joint, it’s usually called a u-joint. When there are two (like the one I blew up on my Jeep recently), it’s called a double-cardan or CV, even though it’s not really a constant-velocity joint. No one ever talks about a single-cardan joint.

    The backwards/upside down one I love is gearing. “I’m going to lower my gears from 3.55:1 to 4.10:1.”
    huh?

    1. [quote]Suspensions are funny because major differences in ride, handling and character are wrung from tiny geometry tweaks.[/quote]

      This is true, which will tell you something about the horrors of swing-axle suspension — an early Corvair had 16.25° of camber change through its complete suspension travel (about six and a half inches). Holy Snap Oversteer, Batman!

    2. That’s the term because you go down the gears to a lower gear.

  3. Nowdays, MacPherson struts are being put on heavier cars, and on heavy 4×4 SUV’s, of which, most off the people who buy them will rarely take them off road, but some will, believing they are true off road vehicles, even when usually called, car based or crossovers.
    So my question or concern is this. Are stuts really strong enough for these uses, usually reserved for double wishbone or solid axles. Has the diameter of the piston rod increased, or is there an increase of the strength of the steel used for today’s struts, to keep up with the increasing demands placed on them.
    I would like to know.

  4. “Strength” is a matter of definition. Are modern MacPherson struts physically robust enough for their intended use, in terms of bending stiffness and so forth? Sure. Do they incorporate shocks beefy enough for heavy-duty off-road use? Rarely. Very few modern vehicles are really set up for that kind of abuse, since less than 5% of them are driven off road at all, even fewer in any serious off-roading; the shocks are usually designed for a civil on-road ride. If you take a Mazda CX-9, say, off road, you’ll probably kill the struts in short order, not because the struts lack bending stiffness, but because the dampers will be overloaded.

    The real limitation MacPherson struts present for severe duty is not the physical strength of the strut itself, but the way the strut transmits its loads into the body. In an SLA suspension with the spring between the control arms, the spring loads are taken by the control arms and transmitted either to the frame (on a body-on-frame vehicle) or, on most modern cars, a front subframe. With MacPherson struts, or with the suspension layout used by old Ramblers, Falcons, and Mustangs (with the coil mounted on the upper arm), the spring loads are transmitted into the structure of the upper fender. (That’s why MacPherson struts are almost always found on unit-body vehicles.) For on-road use, that’s rarely a problem, but for heavy-duty use, it can impose severe, uneven loads on the body structure. You could make a strut strong enough to deal with the loads on the strut itself, but the fender is another matter.

  5. I see that Ford has switched to SLA for the 2011 Explorer as opposed to the MacPherson strut set-up on all their other D platform cars.

    Why do you think they did that? Does SLA provide greater wheel travel or greater durability or some other advantage an Explorer would demand over say, the Flex?

    1. I’ve heard conflicting information about this. A couple of press reports say the new Explorer’s front suspension is an SLA set-up carried over (which I find unlikely) from the outgoing model, but Ford’s own official website says the new model has MacPherson struts, like the other D3 vehicles.

      MacPherson struts present a number of disadvantages for off-road vehicles (scrub radius with fat all-terrain tires, and the way they transmit load to the body structure), but Ford is not positioning the new Explorer as a hardcore off-roader. I would imagine that for Ford, the loss of commonality would probably outweigh any mechanical advantages, especially given that the market for the Explorer is a big question mark — sales of the existing model cratered long ago, and it’s unclear whether the new one will revive them.

      1. Yeah, I noticed the confusion as well but in the end i assumed the press release was right.

        1. First generation Mazda6, whose platform was shared by first-gen Ford Fusion and Ford Edge, had SLA front suspension. The D3 platform has MacPherson strut front suspension. It’s likely the SLA suspension will be phased out with the demise of the first generation Fusion. There was some confusion on this. Even the Mazda website was confused about whether the pre-Skyactive second-gen Mazda6 had SLA or strut front suspension.

          1. As a side note, I happened to learn the etymology of the term SLA suspension, which is not short-long-arm as you might expect. Cadillac applied that term to its first IFS prototype (around 1932), which had what became the early GM double wishbone suspension (with upper arms doing double duty as part of the lever-action shocks). Since that car also had a special aerodynamic body, it was dubbed SLA for Stream Line A, although there was apparently never a Stream Line B or C.

          2. BMW motorcycle’s “TeleLever” front suspension is a form of “modified” MacPherson strut. There are two sliders, one on each side of the wheel, these are sliders only. It uses a separate coil-over-shock that acts on the A-arm.

          3. Thanks for the information. I freely confess I know basically nothing about motorcycles and so I can’t speak intelligently about motorcycle engineering practice.

  6. I’ve sort of followed this progression with bemusement.

    When I was coming of age in the 60s, almost all American cars used unequal A arms in front (Chrysler used a torsion bar variant).

    By the early 70s, after some European and Japanese cars started appearing with struts, references to MacPherson struts appeared in ad copy constantly, it was a badge of sophistication.

    Then in the 80s, manufacturers (and ad copy writers) rediscovered A arms again, and that was the new mark of a sophisticated car.

    Now I’m waiting for solid axles to return (actually I own a Jeep Wrangler, so I am still on solid axles)

  7. Well, it’s not [i]just[/i] a matter of engineering fashion. Now that most cars are unibody, and very rigid, MacPherson struts are a lot more practical than they were 40 years ago. While struts have some downsides, they also have significant advantages. Most A-, B-, and C-segment cars have MacPherson struts for both cost and packaging reasons — it’s cheap, and it doesn’t take up a lot of internal space, important with small transverse-engine cars. Many D-segment cars use them, as well, because it’s an easy way to reduce production costs that most customers don’t perceive or necessarily care about.

    Because SLA or double wishbones are generally more expensive, heavier, and take up more space, they’re now sort of a luxury. Designers have to consider whether the advantages in ride and handling are worth the cost. For a high-end sports car, it might be; for an inexpensive B-segment hatchback, probably not.

    I doubt that [i]front[/i] solid axles will make a comeback — for anything other than off-roaders, the drawbacks are steep. Torsion-beam rear axles, though, are almost as common as MacPherson struts on smaller cars. Even Honda opted for a torsion beam for the Fit and the European Civic.

  8. Had to get my 2 cents in here regarding camber gain with struts. Camber gain can be achieved ,though very limited,if the inner pivot of the control arm is located higher than the ball joint in the static position. As body roll compresses the strut, the ball control arm pushes the wheel outward creating a bit of negative camber which will cancel some of the positive generated by the roll. The down side is a change in track during cornering as well as straight line travel. Raising the inner pivot will also raise the roll center which will affect the handling as well. A friend and I played with this mod on both front and rear drive autocross sedan years ago, and were able to gain some improvement in overall handling and cornering force. The big downer was heavy tire wear due to scrubbing as the track changed. Fun to experiment with though!

    1. That makes sense, and certainly, different manufacturers have found various tricks to mitigate some of the geometry limitations of the classical MacPherson strut (BMW and more recently Ford spring to mind). Of course, as you found, some changes are more suitable to the track than the street!

  9. An observation that may be worth adding is that on cars with MacPherson strut suspensions, the tire tread wears out on the edges much, much sooner than in the middle, even with camber correctly adjusted. On my Audi, tires show virtually none of this, and tires last a good deal longer.

    Another observation that may be worth adding is that in a conventional MacPherson strut using a single ball joint where the lower arm meets the wheel carrier, this ball joint resides on the steering pivot axis, and is thus aligned with the centerline through the strut. However, the strut is generally not perfectly vertical, and the steering pivot line typically insects the ground somewhere under the tire contact patch, as opposed to a point vertically under that ball joint, but also not at the center of the contact patch. Some cars, notably certain BMWs, replace the lower arm with two arms, each with an independent ball joint, the effect of which is to replace the single physical ball joint with a virtual steering pivot point located further outward. The strut has to be angled further from vertical to accommodate this, but not nearly so much as would be required to accomplished the same effect (causing the steering pivot line to intersect the ground plane at the middle of the contact patch) using a single ball joint located on the inner edge of the wheel carrier. The principal advantage is probably not with any handing improvement, but more likely with reduced tire wear and possibly greater life of the ball joint.

    As anyone who studied elementary geometry in high school may recall, a triangle is fully defined by any three parts. If at least one of those three known parts is a side, then the size of the triangle as well as its shape is determined, but even when the three known parts are angles, the shape is fully determined. You will have no difficulty figuring out that the lower arm corresponds to one side of a triangle, and that the chassis is effectively another side of a triangle. The upper mount point for the strut is basically a lazy suzan, and the distance between that point and the pivot joint for the lower arm is another fixed side of the triangle. That gives you two parts for the triangle, which tells you that no other part of the triangle can be fixed, least all the other parts of the triangle also must be fixed, in particular the angles at the ends of the lower arm. But the strut itself joins to the chassis at a fixed angle. As the suspension compresses and the wheel camber changes, the angle of strut body changes relative to the chassis. The upper rod remains at the same angle relative to the chassis, albeit rotating to accommodate steering rotation. It is thus apparent that it is necessary for the strut itself to flex, but none of the articles that I have thus far encountered have made any mention of this fact, which seems to me a defining characteristic of the MacPherson strut. I am interested in other people’s comments on this aspect of the MacPherson strut, and whether anyone has reliable knowledge of just how much flex is required.

    1. R.E. the location point of the top of the strut. The top of the strut is not a fixed point at all. While the strut may in fact flex, or bend to a certain extent, the amount is negligible unless the design loads are exceeded. For instance, fitting larger, sticker tires. Rather, it is located in a rubber mount, both for the purpose of isolating it to reduce NVH trasmission into the body structure, and to allow for the aforementioned camber gain/loss. These mounts also serve as a path for virtually all of the vertical load transmission as well as a portion of the lateral loads. As you might expect, they are highly stressed, and, depending on how well engineered they are, and the quality of the material used, in some vehicles they tend to wear and fail fairly rapidly. As a VW technician, I see this quite often, especially in the older A3 and A4 body Golf/Jetta.

  10. I’m a faithful reader of your blog, but there is a true mistake for this article : the first Ford Vedette was not the first production car with MacPherson struts.
    It’s a common mistake, but the first Vedette used the common SLA arrangement for front suspension.
    You can see a picture of the frame here :

    There is more explanation (in french !) in the message of Vega 770_0 posted 01-12-2009 (21:42:28 pm).
    In fact, the very first was the Ford Consul/Zephyr in 1950. Then, the second generation Ford Vedette was launched with MacPherson suspension in 1954, a few weeks before the takeover of the Ford SAF by Simca. The third one was the German Taunus 17M P2 three years later.
    Surprisingly, as far as I know, the first non-Ford MacPherson car was the Peugeot 404 in 1960…
    Moreover, I’ve seen in some Revue Automobile Suisse catalogs that many japanese brands started to use it in the sixties : Honda already had it on the tiny N360/N600.

    1. Thank you for the correction and the photo — I’ve amended the text accordingly.

  11. what were the earliest Ford models to use these struts in their suspensions (early 1970’s, I think)?

    1. Well, the first Ford product to have MacPherson struts was the Consul. The first Ford marketed in the U.S. with MacPherson struts? A number of European Fords were sold here in very limited numbers by dealers with English Ford franchises, so there were some Cortinas floating around in the mid-sixties. The first to be marketed here in any coherent way, maybe the Capri, followed by the Mk 1 Fiesta.

      The Fox platform used what Ford called modified MacPherson struts (which meant that the coil spring was mounted on the lower control arm, rather than on the strut). I think the first unmodified U.S.-specific car might have been the first-generation, U.S.-market Escort, although I’d have to check.

  12. Tom: I’ve wondered the same thing. In my mind, there needs to be some pivoting or flexing in the strut, otherwise it will bind. I asked some years ago on the AtlasF1 forum, and all I got were blank stares.

  13. Tom, the upper mounting of the strut is not a fixed point. While it is a bearing that allows the strut to rotate for steering purposed, the bearing itself is mounted in a very compliant rubber mount. As the strut compresses and extends and the angles change, the mount has enough range of motion to allow the angles to change without flexing the strut. Having said that, there is a certain amount of flex that does occur, as it must, but strut tubes and pistons are quite robust (in most cases, there have been some notable exceptions)and generally keep the tire located within the intended range of caster and camber.

    In regards to your mention of BMWs use of seperate lower links to create a lower arm, there is indeed a distinct handling benefit to it. The idea is to bring the center of the steering axis closer to the center of the contact patch, thereby reducing the scrub radius. Scrub radius is the arc the contact patch travels through as the wheel is steered left to right. A large scrub radius is undesireable, as it tends to create a “pull” felt at the steering wheel, especially when there is a difference in traction between the left and right wheel. As you noted, there is another problem associated with this is SAI, or steering axis inclination. That is the angle of the steering axis when viewed from the front of the vehicle as it is tilted toward the middle of the car. It has a very profound effect on wheel camber as the wheel is steered from straight ahead, and not in a good way. SAI tends to cancel out caster on the outside wheel in a turn, and multiplies it on the inside. Large SAI’s can even push the outside wheel into a positive camber angle. A good example of this is the Volvo 240 series. Just turn the wheel full lock in one direction and look at the wheels to see what I mean. Typically, you will find that the better handling cars (those that turn in well and remain relatively neutral, or even oversteer slightly) have low SAI’s. VW/Audi found an interesting solution to the problem with the B5 Passat/A6, by using 4 individual links to create 2 wishbones. The result was a nearly vertical SAI. The actual steering axis in this case was not even fixed. Rather, because of the movement of the joints, it moves also in an arc of its own.
    A facinating subject for sure. Hope this clears away some of the fog.
    Regards.

  14. Very informative piece, most of which I already knew, but with a few surprises. The only thing you missed is the inverted strut used on rally cars, where the piston in the strut carries the wheel spindle and balljoint, and the damper end fits into the wheel arch ( to reduce unsprung weight ).

  15. Aaron,

    Two quick notes.
    By some accounts, HiPer Strut is a Saab invention. For instance, Autocar (UK) writes that “This front suspension set-up was designed by Saab engineers for General Motors’ Global Epsilon project.” I’m sure the patent application lists the actual inventors, but I couldn’t find it.

    One of the key elements in scrub radius is wheel offset. It’s also something that amateur suspension gurus almost always get wrong when they “tune” cars by lowering them, fitting bigger wheels, and sometimes even adding wheel spacers. It’s very easy to add an inch or more of offset to a car, or even to take it for negative to positive offset (or vice versa), with dangerous results.

    1. Bernard,

      You make a good point about offset, although the impact of altering the design offset of a car’s wheels is sort of outside the scope of this article. There’s a lot of complexity there that’s really a separate topic.

      I hadn’t seen the item about Saab designing HiPer Strut, although it would make some sense. Saab really got a lot of criticism for the torque steer of some of the more powerful later 900 variations (particularly the Viggen, as I recall), so their engineers may have been giving the issue a lot of consideration.

      As far as patents go, there may not be any specific patents for HiPer Strut per se. There may be for certain specific elements of it, but as the article explains, there’s a lot of prior art in this area. Even with Toyota’s earlier Super Strut, there was no single patent that was recognizably the production layout (I wish there had been because it would have made it easier to figure out the mechanics!), although there was a whole series of patents covering certain elements. One included illustrations of something like a dozen possible variations.

  16. By the way, Colin Chapman didn’t abandon strut rear suspension on the Elan. He abandoned the trailing arm location, using a wide-based lower “wishbone” to control lateral and fore-and-aft location, and rubber doughnuts in the drive-shafts.Some modern aftermarket replacement Elan chassis do use double wishbones instead of the original struts,however.

    1. Thanks for the clarification. Splitting hairs, I would still not call the Elan’s rear suspension a Chapman strut layout — although some contemporary press articles did — because the halfshafts don’t provide lateral location in a way the halfshafts do on the contemporary Jaguar or Corvette Sting Ray independent rear suspensions. I’d just describe it as a MacPherson strut located by a wishbone.

  17. I thoroughly enjoyed reading your article about Earle, my great uncle. I never got to meet him, but I do know a few things about him. I didn’t know he had a short temper, but it doesn’t surprise me because he was such a genius and was a Scot. I love knowing stories about him. His father was an inventor, as well. I have some photos of Earle as a young man and in his WWI uniform. I wonder if you would like to see them!

    Thank you for the great article!!

    Liz

    1. Liz,

      I would love to see pictures of him earlier in his life. If you like, send me a message via the contact form.

      I don’t know that he had a <em>short</em> temper per se, but I got the impression that he was a person of strong opinions and didn’t suffer fools gladly. Admittedly, many of the anecdotes of people who had run-ins with him at Ford were in situations where someone was doing something they technically weren’t supposed to be doing or were just horsing around. For instance, there is an amusing story about some of the designers putting a giant plaster elephant in a wind tunnel where they were supposed to be doing aerodynamic testing, which I imagine was particularly infuriating to him because Ford was renting the wind tunnel by the hour!

  18. I cant help thinking that the passenger area of the Chevrolet Cadet prototype looks remarkably like that of the Vauxhall Wyvern, Velox and Cresta of the mid-fifties(Vauxhall is of course GM owned) .Could that Cadet six cylinder engine have also found its way into the Velox and Cresta, as the size and output seem remarkably similar?

    1. The stylistic resemblance is no great surprise, given the way postwar career advancement typically worked in GM Styling (and for that matter Ford). It wouldn’t have been terribly surprising to have at least a few of the same people have either worked on both or remembered seeing the earlier car, although it may have simply been a reflection of common styling trends.

      As for the engine, I think the resemblance is coincidental. My understanding is that the Velox/Cresta engine was essentially the 1952-vintage 1.5-liter four with two additional cylinders, and I don’t know that there was any relationship with the experimental Cadet engine beyond the broad similarities one saw between various GM OHV engines of similar vintage and displacement. (The Vauxhall six shares the 3 1/8-inch bore of the Victor four, versus the Cadet’s 3 1/16-inch, giving 2,262 vs. 2,173cc.) Vauxhall would have had to buy the Cadet design from Chevrolet — with a markup, in all likelihood — so I don’t think there would have been any particular advantage in using it versus one developed by Vauxhall itself. Vauxhall had been using OHV engines for 20 years and didn’t really need any technical help in that regard. The same logic is how GM ended up with no fewer than FOUR distinctly different 5.7-liter V-8s 15 years later!

      Vauxhall did, of course, offer its own Cadet for a while in the thirties, although there was no relation.

  19. This is easy for me to say 70 years after the fact, but if MacPherson had played up the superior handling of the fully independent suspension, the Cadet could have been the starting point for a sports sedan in the mold of the Rover P6/Triumph 2000/BMW Neue Klasse.

    Of course, it’s easy to see why this didn’t happen. The brief was to design an inexpensive compact, not a car for a market segment that wouldn’t exist for another 20 years. Sports cars were very much a niche market in the U.S. at the time. Earle MacPherson, much less GM management, couldn’t have been expected to think this far out of the box.

    1. I don’t really think the sport sedan in the modern sense was really on anybody’s radar at that time. I think for the most part, even when engineers considered the subject of handling, it was typically prefaced with “ease of,” which isn’t quite the same thing. The standards for maneuverability were somewhat higher in markets like the U.K. or Italy, where narrow, winding roads not originally intended for cars were commonplace, but in the U.S., “handling ease” was generally about stuff like steering effort and how wieldy a car was in tight spaces or for parking. The bigger preoccupation, and what I assume was MacPherson’s principal argument for independent suspension, was getting a smooth ride on what for an American car was a ridiculously short wheelbase.

      Mostly, I don’t think the cultural factors would have been present in the forties or fifties for a sporty sedan to catch on beyond folks like Tom McCahill and a small class of people Detroit generally dismissed as cranks well into the seventies. Some buyers would probably have been pleasantly surprised, I imagine, but even the later American enthusiast crowd would probably have judged it mostly on its suitability for having a big V-8 jammed under the hood.

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