Mishimoto Fiesta ST rear strut brace prototype

Flex-Free Cornering. Fiesta ST Trunk Brace R&D, Part 3: Functional Prototype and Test Rig

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
Mishimoto Fiesta ST performance parts
Mishimoto Fiesta ST performance parts
Mishimoto Fiesta ST performance parts

Everything fit nicely and bolted into position as designed. Check out a close-up shot of fitment with the lower tray support.

Mishimoto Fiesta ST parts
Mishimoto Fiesta ST parts

With the lower tray in place the bracing is barely visible.

Mishimoto Fiesta ST parts
Mishimoto Fiesta ST parts

Although this unit fit well and is extremely robust, we are going to make a couple tweaks. Because this bar is thick and heavy, we need to consider the added weight. The projections near the mounting flange will be eliminated. By trimming this feature, we can reduce the weight of this bar significantly. This portion of the design was in place for aesthetic purposes, so removing them will not impact performance.

Check out a couple shots of our raw prototype before we modify it for testing purposes.

Mishimoto Fiesta ST parts
Mishimoto Fiesta ST parts
Mishimoto Fiesta ST rear strut brace prototype
Mishimoto Fiesta ST rear strut brace prototype

Testing Rig Fabrication

Taking information and experience from our recent Mustang strut bar testing, we will be using a digital linear displacement gauge. This device will record object movement, which we can use to compare movement of the rear of the Fiesta both with and without a brace in place.

First, we cut our prototype in half.

Mishimoto Fiesta ST rear strut brace prototype
Mishimoto Fiesta ST rear strut brace prototype

Our team needed a method to stabilize this bar during movement to keep the bar from moving in a vertical direction. We devised a piston and cylinder assembly that was machined on our lathe and welded to each cut end of the center portion of the bar.

Mishimoto Fiesta ST rear strut brace prototype
Mishimoto Fiesta ST rear strut brace prototype

After some precise TIG-welding, our testing setup was complete.

Fiesta ST parts testing
Fiesta ST parts testing

This setup will provide a displacement of the distance traveled as the two sides of the body flex in either direction.

Fiesta ST performance parts testing
Fiesta ST performance parts testing

This setup will work perfectly for testing the flex on a Fiesta without any bracing. Once that data is captured, we will tack weld steel in place to support the bar as if it were one piece. This will provide the displacement data for our Fiesta with the rear strut brace in place.

Fiesta ST performance parts testing
Fiesta ST performance parts testing

Coming Up – Testing Data

We have some interesting plans for this testing device. Next time we will explain our plans for testing, conduct the tests, and present our findings.

Thanks for reading!

-John

Leave a Reply

Your email address will not be published. Required fields are marked *