How the Ford GT's trick suspension has two unique spring rates


The second-generation Ford GT packs incredible engineering no matter where one's eyes may scan. Be it aerodynamics, engine technology, or the suspension, there's always more than meets the eye. Here, however, we're talking about the GT's suspension, which is anything but traditional. It uses coil springs, but in a very unique way, as well as electronically controlled Multimatic eDSSV dampers

Sounds like a setup for someone to explain, and thankfully, Jason Fenske is already on it in his latest episode of Engineering Explained.

The GT features a double-wishbone suspension, but it's not of the garden variety. It also uses pushrods that actuate both the dampers and the springs, and its party trick is that it has two types of springs at each corner, giving it two spring rates.

At each corner, the pushrod connects the lower and upper control arms with a rocker. The rocker acts on both the electronic damper and twists a torsion bar that acts on a coil spring. As the pushrod provides force, the torsion bar rotates, and it, in turn, compresses and expands the coil spring. The torsion bar and coil spring provide two unique spring rates, one for each ride height. In regular driving modes, the GT's ride height sits at 4.7 inches (120 millimeters), but Track mode drops the ride height to 2.75 inches (70 mm), a drop of about 2 inches.

So, that's what going on in the system itself, but back to the supercar's trick: the spring rates and ride height. At the GT's highest ride height the torsion bars and coils act in series. Therefore, the equivalent spring rate of the two springs in series is less than either one of them. When the driver engages Track mode, a hydraulic actuator at the base of each coil spring locks the spring so it no longer moves.

That leaves just the torsion bar as the acting spring for a higher spring rate than both components combined. Why does the Ford GT need a higher spring rate at a lower ride height? Since there's now less suspension travel, it helps keep the car from bottoming out. It's especially true as downforce pushes the car even lower for greater aerodynamics. No one wants their GT scraping the ground at high speeds.

Check out Jason's full explanation, complete with a suspension animation, up above.

 
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