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MacPherson and Pseudo MacPherson suspension

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MacPherson suspension

The system was invented in 1955 and used on the first Ford Consul. The MacPherson suspension is a technology for front and rear suspension. It is an independent suspension type, including a single suspension arm (spring and damper), an anti-roll bar and a lower arm. The junction between sprang and unsprang masses is carried by a ball joint on the wheel side and a side frame axis (to allow different suspension settings). The system spring – damper is attached to the hub carrier. This arm is also used as steering axis.

MacPherson Suspension

The damper has two missions, dampen relative movement between the wheel and the body and participate in the kinematics of the wheel plane via the anti-roll bar and the lower arm. The damper rod has a larger diameter (25mm) than a damper (14mm) used in other suspension types.

Main advantages:

  • Easy assembly
  • Ratio cost / performance
  • Mass
  • Lateral dimension
  • Spring and damper motion ratio equal to 1 (damper displacement/spring displacement = 1)

Main disadvantages:

  • Precision
  • Vertical dimension
  • Friction
  • King pin offset
  • Limited possible settings
  • Low camber gain

Pseudo MacPherson suspension

The difference between a “real” MacPherson and a Pseudo MacPherson suspension is the addition of a lower wishbone. Thus, the guidance of the wheel plane is no longer provided by the lower arm and the anti-roll bar but by the lower wishbone. The advantage of the Pseudo MacPherson is that you can choose to not use an anti-roll bar. This reduces production costs and the weight of the suspension. For light vehicles, the spring stiffness may be sufficient to ensure proper maintenance of the body roll. If an anti-roll bar exists, then it is attached to the spring-damper via a rod (see illustration).

Pseudo MacPherson Suspension

Photo credit: GM (Opel Insigna)

Main advantages:

  • Easy assembly
  • Ratio cost / performance
  • Mass
  • Lateral dimension

Main disadvantages:

  • Vertical dimension
  • Friction
  • King pin offset
  • Limited possible settings

There are three front MacPherson suspension types, the classic Pseudo MacPherson (shown above), the Pseudo MacPherson with fictive steering axis and the Pseudo MacPherson with independent steering axis.

The Pseudo MacPherson with fictive steering axis has a virtual steering axis. The lower wishbone is replaced by two arms. This suspension is more expensive than a classic Pseudo MacPherson.

Real and virtual pivot point

The Pseudo MacPherson with independent steering axis allows to unlink the camber angle setting and the king pin angle (via the steering axis). This type of suspension is usually used for race cars. The main disadvantage is the added cost compared to a classic Pseudo MacPherson suspension.

Pseudo MacPherson with independent steering axis

Photo credit: GM (Opel Insigna OPC)

As you can see above, the hub carrier is no longer attached to the damper but linked to two ball joins. Thus, the spring – damper system is no longer used as steering axis.

Conclusion

The Pseudo MacPherson suspension is the best compromise between cost and performance. This suspension is one of the most used in the vehicle segments B1 (iQ Toyota, Renault Twingo, etc …), B2 (Renault Clio, Skoda Fabia, … etc) and even M1 (Audi A3, Mazda 3, etc …).

  1. David Cameron
    David Cameron05-22-2013

    I need to question some of the remarks and conclusions in the article.

    “The Pseudo MacPherson with independent steering axis allows to unlink the camber angle setting and the king pin angle (via the steering axis). This type of suspension is usually used for race cars. The main disadvantage is the added cost compared to a classic Pseudo MacPherson suspension.”

    Not really, the static camber angle setting is determined by the machined surface on the suspension knuckle. You can machine this surface to +- 10 degrees if you desire. As most static camber settings are +-2, you have sufficient authority to generate the desired static camber angle.

    The use of a new term “Pseudo MacPherson strut, does nothing but confuse the casual reader. The original work did use the combined functionality of a rigid link( a lower lateral load bearing element) and the fore-aft section of the stabilizer bar as the longitudinal load bearing element. So that system always had the functionality of locating the lower ball joint for suspension location.

    I have also never seen a passenger car without a front roll stabilization bar. The only place I have seen the elimination of the roll bar is in systems with a transverse leaf spring OR commercial vehicles.

    An added benefit for the MacPherson strut( either flavor) is that the loads transmitted to the unibody architecture are of a 1:1 magnitude. As you look to apply other suspensions to unibody systems you see the issue with resolving the increased local loading generated by the so-call linkage ratio of the spring.

    Finally your remark as it pertains to the attachment of the stabilizer bar in your Pseudo MacPherson strut.

    “The advantage of the Pseudo MacPherson is that you can choose to not use an anti-roll bar. This reduces production costs and the weight of the suspension. For light vehicles, the spring stiffness may be sufficient to ensure proper maintenance of the body roll. If an anti-roll bar exists, then it is attached to the spring-damper via a rod (see illustration).”

    The stabilizer bar can be attached in a variety of ways to the lower control arm. The example cited in the Oper requires that the link for the stabilizer bar be required to have rotational capability so as not to bind the steering of the vehicle. Further, In the Opel example as the steering is changed during a cornering manuever, as the attachment of the rod to the strut is not on the steering axis, the roll stiffness of the vehicle will change.

    • Charlie Constant
      Charlie Constant06-26-2013

      Hello David,
      Your feedback on this article is very interesting and give us more details concerning this type of suspension which has been used for decades and has seen lot of improvements. Don’t hesitate to comments on others articles.
      Charlie

  2. dave
    dave08-14-2013

    Hello, i want to know, what is the best, pseudo macpherson independient, or macpherson, and for a rural way?? Thanks..

    • Charlie Constant
      Charlie Constant08-14-2013

      Hello Dave,

      Pseudo MacPherson suspension is actually the best suspension for small passenger cars due to reliability and very good ratio cost/performance. The independant version of this suspension is mostly used on sport cars and is more expensive. The traditional MacPherson has no big advantage compare to the Pseudo MacPherson. So my choice would go for the Pseudo Mac Pherson for a “city” car.

      • Marvin McConoughey
        Marvin McConoughey12-03-2013

        The MacPherson strut is used on several upscale cars. Some BMW and Mercedes-Benz models come to mind and there may be others. Question: Are there any inherent limitations imposed by this type suspension on upward wheel movement?

        • Charlie Constant
          Charlie Constant12-14-2013

          Hi Marvin,
          Thanks for your comment on this post. The MacPherson strut is not very used on new cars but the pseudo MacPherson is used a lot. So, regarding the MacPherson, it has strong limitations on camber gain on upward wheel movements. The Pseudo Mac Pherson doesn’t have this limitation due to the use of a lower wishbones (instead of a simple arm and the anti roll bar playing the role of wishbones).
          For both suspension, vertical dimension is a limitation in term of space in the wheelhouse.
          I hope this answer to your question.
          Don’t hesitate to contact us again for any others questions.

          Charlie

  3. Han
    Han02-08-2014

    If im not mistaken this was used back early 2000′s on the Toyota AE111….

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