Posts Tagged ‘shelby drop’

Why Relocate the Control Arm?

June 27th, 2009 No comments

So, why the so called “Shelby Drop”? First, let me explain just what it is. The “drop” refers to the fact that the inboard mount point of the upper control arm is moved down. Shelby moved it down 1″,  and 1/8″ rearward. It would probably be more accurate to call it the “Arning Drop” because it was originally designed by Klaus Arning, a top suspension designer for Ford. He designed it as part of a full package for the Mustang, which included his 4 link Independent Rear Suspension design. The 4 link IRS didn’t make it into the final car, but Shelby made use of the front upper control arm positioning for the GT350. In my highly approximate picture of the stock setup, you can see why: camber_curveThe circle represents the path of motion of the outboard control arm mount point during suspension movement. You can see here that if the suspension is loaded, as in a hard turn or a bump, the control arm will move outward, pushing the top of the tire out, creating positive camber. This will make it so that the contact patch of hte tire is reduced, with just outer edge of the tire contacting the pavement.

You can imagine what happens when you move the mout point down a bit. The curve becomes more advantageous to the loaded condition. If the car is in a hard turn, it will actually be beneficial to have a bit of negative camber to maximize the contact patch of the tire.

The drop also lowers the CG a little, and reduces the leverage that the suspension has on the body, minimizing body twist. These 3 things together make for more performant handling under the stress of the track.