The testing of our Fiesta ST rear strut brace involved three different driving conditions.

Cornering: 30-40 mph, slalom

Braking: 50-0 mph, stop with ABS engaged

Acceleration: 0-60 mph, full-throttle run

Each setup (with and without brace) was tested on the same day on an identical surface and with the same driver. The tests are repeatable and will provide an accurate comparison of rigidity in the rear body portion of our Fiesta.

Results

Check out the plot below to see our testing results.

Fiesta ST performance results

These data points confirm our theory that the addition of bracing in this area of the ST does indeed have an impact on flex. Although flex in these conditions

In our last update, we left you with some mock-up prototype pieces that we used to create and refine our Fiesta ST rear strut brace design. Since then, we've worked up a couple of functional prototypes to test our ideas for stiffening the rear of this hot hatch.

Initial Prototypes

We constructed two prototypes of this trunk brace. The first prototype is finished in a black powder coat, and we'll use this unit to evaluate for aesthetics and fitment. The unfinished ("raw") prototype is going to be used for testing purposes, meaning it will be modified.

First, check out our powder-coated unit bolted into place.

Mishimoto Fiesta ST performance parts

We left off development with a neat look at our first prototype, when we determined the shape and path of our brace and printed out mounting brackets for each side of the piece. By using specific angles with our square material, we were able to avoid modification of the seat mounting bracket, retain rigidity, and provide a bar that is easily hidden by the rear tray.

Our last image showed our fabricator tacking together the material. Below is what we ended up with.

Prototype Fiesta ST rear strut brace installed

We then installed the floor panel mounting covers.

Chassis rigidity is extremely important for on-track handling, response, and feel. Ford provides a well-designed chassis with the Fiesta; however, as you can imagine, there is always room for improvement. Within the short time that this car has been available, the aftermarket has provided some great options, including better dampers, stiffer springs, and thicker sway bars, to enhance handling.

Our company will not likely dip into struts or springs, but we are certainly interested in helping stiffen the chassis. Our Mustang EcoBoost front strut tower brace is underway, and we recently launched development of a Fiesta ST rear strut brace. Time to get started!

What's The Plan?

Our goal here is to link one side of the rear trunk area to the other. You may wonder why this is needed. Doesn't the floor/body connect the two sides? Yes, but keep in mind, the floor is not made from a thick material. During aggressive cornering, the floor will see some pretty