Why do we need strut tower braces?

[Pete K]

This is completely around the wrong way, but I've just about finished making my strut tower braces so now I'm wondering, What do they do? I've asked many people and got two distinct "camps":

1 - They improve handling by stopping the body flexing and therefore, maintain the geometry better.
2 - It stops the strut towers from cracking when you consistently drive hard in a lowered car.

Does anyone have any documented evidence as to which it is, or if it's something else?

Cheers

[Karl in KS]

Improve handling. I noticed that the front end was a little more responsive after I installed my strut brace.

[Brian Smith]

There are a ton of effective things that can be done to increase the cornering performance of a car. For cars that are driven in competition seriously, strut braces (as well as other chassis braces) are probably worthwhile expenditures. For myself, I wanted to relocate my battery for practical, convenience purposes, and the strut braces from Top End were a good way to achieve that.

My favorite myth was one my father had for buying a front strut brace: that his aged unsupported strut tops were going to collapse together on his unibody car from 1981 when encountering a significant suspension bottoming dip in the road. I doubt that anyone here believes that one.

[larsobg]

Isn't that what they call lawyers in OZ. (That's a nickname for Australia, or do you need documentation on that).

Most REAL car enthusiast simply accept the fact that we must make up a lot of car modifications to improve our rides, without needing significant evidence of the shortcomings of the car, or evidence of the improvements rendered by our cutting, drilling and welding of new attachments.

I used to race an early Austin Healey 100/6 and when I started racing it, it had numerous faults on the track. Body roll and body flex were just the beginning. Lock to lock on the steering was considerable, so I shortened the pitman and idler arms. Steering response to turns on the wheel became much faster, but the strength needed to turn the wheel also increased a bunch. I consider that the Healey required the same strength to steer as a US Army 2 1/2 ton truck (deuce and a half) being raced on Laguna Seca. I had the good fortune to race such a truck on Laguna Seca when I was in basic military training at Fort Ord (near Monterey) in 1964.

I subsequently sold the Austin Healey to another racer. After his first run, He commented, "Hey, this thing corners like a TRUCK". My point is made. How does one document that. We didn't have YouTube and Video Tapes in 1964. I do submit however that all my mods to the Healey were "improvements" to the vehicle.

I also know that the e12 has one characteristic flaw in body design and construct. If you have one that emits an intermitten snap or creak in the cabin, you simply have to pull the headliner back from the B pillar and look for a crack in the sheet metal starting where the B pillar welds into the roof on the inside of the car. When the body rolls, this crack has a deep snaplike creak during hard cornering. If one has the tower braces in the car, that crack likely does not occur.

Unibody construction inherently flexes based on how hard a car is driven. It's likely that BMW 5 series cars are driven harder than most average early unibody constructions. A lot of unibody construction over the years has been spot welded rather than seam welded. Spot welding allows better response to body roll than seam welds.

All e12 bodies are full seam welded, which turns out to have been a less durable way to construct unibody.

Therefore, anything you do to counter the flexing of the e12 body will result in less work hardening of the metal and cracking of the sheet metal ADJACENT to full seam welds, like around the base of the rear shock towers.

There, now you have documentation. If you print this out and file it, it will be considered as a document explaining strut bracing. My Documentation.

Next thing you know, you'll be querying us for documentation on whether the the rear differential mount really does develop fatigue cracks over time under hard repeated acceleration. I submit that the repair kit sold by BMW is simply proof enough.

[Pete K]

Thanks Lars.

No need to worry, I've accepted that it needs to be done (that's why I'm almost finished before I asked the question). I was just hoping someone might have some way to get rid of the myths around some of these things.

Some of these myths really get me. Like the one perpetrated by Subaru that all wheel drive gives you more GRIP. Bollocks! Grip is generated by tyres and suspension geometry. Traction is another matter...

Thanks for the info on welding. That's good stuff to know.

Cheers

[1st 5er]

All e12 bodies are full seam welded, which turns out to have been a less durable way to construct unibody.

That makes sense, though I've always thought the opposite.
Is it that 'full seam welding' would allow for less flex and more rigidity and tear?
Does this only apply in, say, track, "high stress", use?

Are you also saying that in a normal driving application, 'full seam welding' is still not as durable?

[Peter Florance]

All e12 bodies are full seam welded, which turns out to have been a less durable way to construct unibody.

Are you sure about that? I've seen a lot of spot welds on my car.
I think they tended to braze or solder some of the seams, which may give the appearance of continuous seams.

I'll tell you where strut tower braces don't help: cowl-cracks. I think that flexing is in a different direction