Rear strut bar/trunk brace diy questions

[OCDFist]

I've never been interested in adding weight in the form of chassis braces, and haven't personally felt a difference they might have, until I made a few for my son's WRX and they worked well. Now I'm interested, starting in the rear for now.

My question, which is worth doing for street enjoyment (no track time)?

- Pierce trunk brace and be done.
- Pierce trunk brace and a DIY horizontal rear strut bar between the top of the towers.
- Pierce trunk brace and a DIY strut bar with angle bars (like the TB Bootcamp brace).
- DIY X-brace, including a horizontal bar between the strut towers and a bar going from the top of each tower to the opposite side of the trunk where the Pierce trunk brace bolts to the floor.

I can buy & TIG weld the 1" or 1.25" x .065" wall chromoly tubing at work so it won't be crazy heavy, but I don't want to spend time or money on braces that won't add to the fun. I'm not showing it off at the track or car shows, just like to have an efficient set up. Stock suspension otherwise.

For those with FiST chassis experience, what do you think?

Thanks!

 

[AnimalMother]

I just got the FiST in the summer, so I was only able to race it a handful of times. Its very taut. Perhaps as rigid as a caged miata with door bars. This is just subjective jibber-jabber, but I still cant imagine any brace configuration doing much... the X maybe, but the other stuff is for car shows.





-dan

 

[M-Sport fan]

^^^I do not have a lot of experience with THIS platform, but on any other uni-body I've worked with/road raced, or autocrossed (which were not even nearly as 'taught' right from the factory as this one is), the bracing options did NOTHING but add sprung weight to the car, especially only for street use.

On those cars, and especially on this one, the ONLY tubing I would ever think of adding to the chassis/uni-body is either a tied-in cage or multi point roll bar, which besides the rollover/safety and chassis rigidity factors also allow the proper use and mounting of harnesses.

 

[OCDFist]

Thanks for the input!

 

[D1JL]

For the upper rear brace, I might suggest aluminum to save high weight.
As for street use I would suggest to make it removable just in case you need to load something.
You can use the rear seat back latch points for your anchor locations.
I offered this design to a few vendors but it was thought too difficult to build and install.
I built mine from scratch and had it installed in a day.

Dave

 

[gronktired]

The fiesta has a twist beam rear suspension. Movement in the strut towers imparts no meaningful side loading at the wheels.

Anyway, here's a wonderfully silly graph from Mishimoto demonstrating an improvement of almost 200 microns.

 

[spoon]

Lol!

 

[Zormecteon]

I have the mountune front tower brace. I don't track the car, so I can't say that the car is faster for stiffer in a measureable way, but what I can say is that some of the creaks a groans from the dash area are gone. The car now SOUNDS solid.

my 2?

 

[BRGT350]

As I have been saying for years, rear shock tower loads are almost pure vertical, with very little horizontal loading. The springs carry the load and they are under the rear frame rails. There is only the opposite force of the shocks being applied to the shock tower. That amount of force is very minimal in terms of the strength of the unibody. Now, the front strut towers do carry the load because the front springs are seated in the towers. I honestly don't think the strut braces (2-point design) do anything of any real value to the strut towers. You would need to triangulate the brace to the firewall or frame, which is exactly how rally and race cars are done.

I would like to know how and where Mishimoto picked up the displacement and under what conditions. Also how many tests were done to determine the data. When I have measured displacement and loading data, I take a number of results since it is common to find fliers in the data and best-fit conditions are usually done for the best data representation.

 

[M-Sport fan]

I honestly don't think the strut braces (2-point design) do anything of any real value to the strut towers. You would need to triangulate the brace to the firewall or frame, which is exactly how rally and race cars are done.

THIS is what I am referring to when I say "tied-into the unibody" full cage.

 

[OCDFist]

Update:

Finally finished my chromoly brace and installed a PM rear brace. Overkill, heck yeah, but I love it. The rear feels planted and the corners on the way to & from work are better . Excuse the mess, it was super cold and I wasn't in the mood to clean.

 

[BRGT350]

it looks really good, but still can't understand how it makes a difference. The shock loading is so small compared to the spring perches. I came out of heavy duty suspension design and shocks need very little support. What do you have that supports the structure behind the mounting flanges and the trim?

from a fabrication and looks standpoint, it is 100% bad ass. I am lost at the functional part. One possibility for the change in stability is the added weight over the rear tires. This moved the F/R weight balance a little to the rear so the back tires get to do a little more work and the fronts a little less.

 

[M-Sport fan]

I also question the functionality of all of the available bracing out there.

I am even reluctant to add the weight of the front lower 2 point, or even four/six point suspension braces which everyone on here swears up and down HAVE TO work, and do something.

 

[AZSP33D]

Old thread -- first of all, this is available as I have purchased the car, and it will be removed (not allowed modification for SCCA STH)

2nd on chassis bracing... the rear suspension movement under cornering twists the chassis by the lower pick up points with a lot of leverage, and bracing to keep things square will make a big difference. This is not like the shocks have any meaningful twisting load, but like adding a strong bulkhead in the unibody, and is well thought out in my opinion. The blue car with stock suspension and no rear sway bar, but a lot of bracing, handles very solid.

 

[PunkST]

it looks really good, but still can't understand how it makes a difference. The shock loading is so small compared to the spring perches. I came out of heavy duty suspension design and shocks need very little support. What do you have that supports the structure behind the mounting flanges and the trim?

from a fabrication and looks standpoint, it is 100% bad ass. I am lost at the functional part. One possibility for the change in stability is the added weight over the rear tires. This moved the F/R weight balance a little to the rear so the back tires get to do a little more work and the fronts a little less.

Its not the shock loading. Its the big empty box between the b and c pillars twisting when you dive into a corner or the road is uneven. The seats do nothing to tie the rear end together. ( unlike a sedan that has the rear package tray sheetmetal between the towers.) A rear brace turned my rattle box of a zx3 into something much smoother and sturdy to drive around. This car will respond similarly.


The front brace does a good job at quelling axlehop. I autocross in smf and. These braces do make a difference in how precise you can be with your lines, ans how much feedback your getting. Id say a good rear brace, a front lower brace ( even just a 2 point) and replacing the i beam brace is one step down from putting a cage in the car. Which in terms of bang for buck and functionality as a street car that has some track fun. It fits the bill perfectly.

 

[Ford ST]

I have had a rear trunk brace on my car for a week now it does make a difference.
The best way I can describe it just feels more solid the rear-end is more predictable. It also helps with excessive rattling. My Wife got it for me for Christmas she got 20% off very happy with the Pierce brace.
This is the only brace the car has on it right now for the moment.

Sent from my LG-LS997 using Tapatalk

 

[TemecFist]

I've used and tried pretty much every brace out there (TB, Pierce, DNA, etc). Heres my conclusion. For a street car, rear braces do nothing except induce more oversteer, especially if you run stiffer springs (Swift) and no/stock rear camber. Oversteer is the last thing this car needs. Front/rear strut tower braces do absolutely nothing, rear trunk brace "might" add some more oversteer, torsion brace definitely adds oversteer. It might "feel" faster or more "planted" but the track times dont lie. For me, the fastest way around a track is no rear braces at all. Get some sticky tires and rear camber plates before any rear braces.