Thoughts on Rear Subframe Braces
 

I searched around, but didn’t find too much info. What are everyone’s thoughts on rear subframe braces, like the Technobrace or adjustable rennline?

Would stiffening the rear chassis help reduce understeer? My understanding is that softening the front and stiffening the rear helps reduce understeer. Or would only a sway bar help with that?

Thanks!

Sway bar does much more, particularly when on sticky tires. We have installed several of the Rennline units, and I have one on my personal car. Some track rats like the adjustability, and having rear tie downs for trailering is a plus.

Thanks, I am finishing up my suspension work and trying to decide if it's worth it "while you are in there." The car will be mainly street with occasional autocross or something similar to learn my limits safely. The set up is currently as follows.

- 2001 Boxster S
- PSS9s set a little lower than ROW M030 height (getting corner balanced and aligned in about a week
- New OEM strut mounts (Lemforder up front and Porsche in the rear).
- New Porsche brand strut bearings up front with new rubber inserts (old ones were trashed from bouncing on lowering springs)
- New Lemforder drop links all around (some were torn)
- Stock "S" sway bars
- Stock 17" wheels with Michelin Pilot Sport tires - 205 in front, 255 in rear (in the future i may do 225 in front)

My thought was to stiffen the rear with a subframe brace and not mess with sway bars for now. Perhaps thats wishful thinking :)

I believe that the rear brace is to stiffen the rear suspension (to help maintain the alignment settings while under load, specially when using sticky tires)

To adjust the over/under steering you need adjustable sway bars, but you also can start experimenting with the tire pressures on the front and rear axles as well to help reduce the understeering..

when you turn the outside wheels see most of the load - the car tries to keep going straight so the bottom of the wheels try to push in which in turn reduces negative camber and contact patch. the concern is that on an oem car the only thing resisting this inward motion at the back is the pressed steel plate which can flex under load - the technobrace adds strength in this area.

conversely, if the bottom of the wheel is pushing in then the top is pushing out which is where strut tower braces come in - they don't need to resist compressive loads they just need to not stretch. hence you can use a light carbon brace or equivalent. personally i think they are useful in the front where the strut towers are not fully triangulated, but at the rear meh - there's a lot of metal in there already.

My experience…
 

I have a front strut tower brace and the Rennline rear lower brace.

I have an M030 factory suspension and run PS4s tires.

I have several DEs under my belt and an autocross trophy or three on my shelf.

I could not tell any difference at all after installing the bars.

But they look cool.

Given that these are bolt on parts, you can always bolt them on later. I think that you will find that the limiting factor to how your Boxster performs will be the performance of the nut behind the steering wheel. I’d suggest that you spend your money on DE, not on trinkets.

But trinkets are so much fun! 😂 sounds like it isn’t a must have. I’ll worry about it later. It’s going to be a completely different car after the coilovers and will take some getting used to anyway.

I made a rear brace using 3/4" square stock aluminum. I have no trinkets, but I feel as though it changed handling around high g turns. It will "stiffen" the rear and reduce the tendency of the rear to walk out under that circumstance for reasons mentioned above. For $25 I think it's a great idea. Fwiw.

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I see it as follows..

To reduce understeer on a oem car, first increase neg camber in the front. The car is setup with understeer "by design" via limited camber..

Technobrace and similar supports the rear "leg" of the rear subframes. The toelink is connected to this leg. The front leg on the rear subframe holds the LCA which is crucial for keeping the neg camber under heavy cornering. This front leg is already supported by a oem steel structure in front of the subframe.
So basically the technobrace keeps the toe stable under load.
A solid inner bushing for the LCA will further support camber under load.

One might not need a rear strut brace in most cases, however I've got cracks in the rear strut tower so after welding this, maybe a brace would protect from further cracks?