We all have purchased aftermarket parts we regretted, recently for me it’s the #RSTBRC Rear shock tower brace “Double Bar” from SMR.
Purpose
Why did I want a rear shock tower brace? I’m always game for gimmicks that can stiffen up the flexible fox chassis. In “theory” the point of this is to strengthen the chassis to help prevent flexing near the rear at the shock towers. The particular product comes with sweet wording such as; limit g-loading, chassis flex and hard cornering… For the low cost of the product, I figured why not try it out.
Product fitment
The first test of a great aftermarket product is the fitment, if it doesn’t fit right, you’re going to have a bad time. SMR’s brace’s instructions will have you bolt brackets to the thin wall of the inner rear fender and bolt the “DOUBLE BAR” brace to the brackets. While the fitment itself is less than desired, you can make it work but the product is clearly made to be generic.
Instructions indicate to install above the shocks, you can’t necessarily install the brackets right above the tower (where the chassis material is doubled) and even if you did, there’s not enough strength at the attachment to make a noticeable difference in chassis flex.
The most appropriate location for the double bar would be at the actual strut tower, however the bar itself will need to be shortened to fit.
Engineering
Fitment aside, the engineering of this product is terrible and there is no way, shape or form that this will do anything but add weight to your foxbody Mustang.
Where the brackets are bolted to (as per instructions) make no sense as it’s one of the softest parts of the fox Mustang. The inner fenders are so thin you can bend it with your thumb. In other words, if there is flex, all this will do is dent the inner fender. The design of this product just doesn’t work.
Suggested product fixes
I’m going to design a proper bracket that will actually help increase rigidity by attaching to the actual strut towers. This will require a stamped steel piece with a slot welded in to provide better load distribution and attachment points. Below are my initial cardboard templates.
Of course this will require modification of the bar itself to fit between the shock towers. The suggested bracket will allow proper stiffening of the shock towers.
To really make a difference, I would also have to not use the middle bar and create my own to form triangulation, perhaps even helping to solidify mounting points for the upper control arms. See the differences in product design below:
Do you really need a rear strut tower bar?
In my honest opinion you don’t really need this, especially for a notchback and more so if you do not have coilover conversion in the back. To really prevent chassis flex at this point you will need some sort of “X” brace around the back pillars / trunk floor where the strut towers are located. To be brutally honest, you will need to engineer a complete front-to-back system to reduce flexing “the right way”. Piecemealed parts will not necessarily add up to a completely rigid chassis. This is the equivalant of adding “HP numbers” on things like underdrive pulleys and CAI and thinking you’ve added 150HP to your otherwise stock 5.0.
However if you insist. I’ve heard positive feedback from those who have strengthened their rear strut towers (the right way). Below is a similar product (not installed on a Fox) that would provide a better fitment and design. Notice the triangulation!
