To know what the heck a control arm IS, we must first explore what the heck a control arm IS NOT. A control arm is not: 

  1. The sample arm that remains the same throughout an arm experiment
  2. A keyboard shortcut to take a screenshot
  3. The winner of an arm wrestling contest
  4. A baseball player’s dominant pitching appendage

Awesome Alliteration!

So…what the heck is it then?

Vehicles have multiple control arms. They regulate the motion of the wheels so that they are synchronized with the movement of the body. In other words, they keep the tires on the road. In other-other words, de holder dekkene på veien. (10 bonus points if you know in which language those words are without cheating!)

They look an awful lot like wishbones, don’t they? Term-naming people thought so too. The configuration of upper and lower control arms is called a double wishbone suspension.

How Do They Work?

As you can see in the image above, the control arms have a wide end and a narrow end.

  • The wide ends connect to the frame of the vehicle with rubber cylindrical bushings through the holes on the ends. That allows the wide ends of the control arms to pivot up and down.
  • The narrow ends connect to the wheels with ball joints. That allows the narrow ends of the control arms to pivot in all directions.

The combination of the pivot ranges of the bushings and ball joints is what keeps the wheels on the ground when the vehicle goes over bumps or hits potholes.


Click here to see a cool animation of a double wishbone suspension in action (complete with rockin’ music) on YouTube.


Signs of Failure

Open up your ears and ready your epidermis. Here are some things that may point to control arm assembly failure:

  • Rattling noise when turning around corners at low speeds
  • Clunking noise when driving over a bump or pothole
  • When the vehicle is suspended (either by a jack, lift, or magician), the wheels can be wobbled easily
  • Shaking steering wheel at higher speeds
  • Vehicle is out of alignment

How does he do it?!?


So, there you have it. Now you know what the heck a control arm is NOT, what it IS, and marveled at the magical feats of Bob the Magnificent.


Tell me what other automotive parts baffle you. I’ll tell you what the heck they are!

Written by Ben Scharff

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