Front Strut Braces

[jimk]

Could someone describe the forces that a strut brace sees.  Other than under hood jewelry, what loads are applied to them.   Why add the weight?

[Schnellvintage]

This might help.  Though, not all cars are built the same.

 

[PhilC]

As far as understand it they prevent the strut towers flexing left and right (full of technical terms me 😆 ) thus keeping the wheels more evenly spaced as the car rises and falls. I put one on my old 911 and it made a huge difference to the handling. They weigh very little generally so you’re not adding anything you would notice.

[cda951]

1 hour ago, jimk said:

Could someone describe the forces that a strut brace sees.  Other than under hood jewelry, what loads are applied to them.   Why add the weight?

 

I wish I could describe the exact forces and load path, but the difference in front end feel is noticeable in a relatively flimsy unibody such as the BMW 02 or early Porsche 911, I notice it on my own 2002tii and in customer cars. 911s in particular hold their set front camber much better using a particular type of front strut brace that attaches to all the strut mount bolts.

 

I would say that by about the 1980s, factory unibody construction was much more robust, so the strut brace became less necessary (zero tangible difference in my Porsche 944 Turbo track car, for example).

 

I do remember reading an interview with a chassis development engineer (I think it was in Racecar Engineering magazine) who operates a seven-post shaker rig, and he mentioned that he had never seen a strut brace make a noticeable difference in any of their measurements. I wish I could find a link or reference, but he was likely referring to modern street car platform versus flimsy 1960s designs . . . .

 

On the other hand, the OE engineers often add strut braces to the firewall of some modern platforms, including at BMW---with the propensity of bean counters outweighing engineering decisions, I would argue that they are there for a reason in these cases. I just wish I could explain why

[jimk]

Doesn't the front structure between the two fenders keep the top of the inner fender assembly from left to right movement.  I could understand on the Porsches with the down sloping front being a lot more flimsy.

The road surface is below the ball joint and the upper strut  mount has a much longer lever to retain movement crosswise.

[Mikesmalaga72]

I found an interesting short read about the actual physics to find if the device was practical. Great question Jim!

Dr. Saabish: On the Physics of the Front Strut Brace - SAABSUNITED

WWW.SAABSUNITED.COM

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 It’s precisely eight past noon.  Normally any resident of the lecture hall would be submerged in complete darkness, surrounded by rows upon rows of empty seats.  Of course, as one would expect, the auditorium’s regular occupants are hard at work preparing for their upcoming...

 

 

[Schnellvintage]

1 hour ago, jimk said:

Doesn't the front structure between the two fenders keep the top of the inner fender assembly from left to right movement. 

Yes, to a point I have seen many front clips with creases at the top edge, where the fender and nose are spot welded.  I have only seen this with stiff sway bars and pushing the cars limits.  I too have felt a more ridge feel during hard corning with wider tires and stiffer sway bars, than without a strut bar on a 2002. I unfortunately don't have a picture of the crease, I'm referring to.

 

Matt

Edited December 4, 2022 by Schnellvintage
add photo

[visionaut]

Good articles with some numbers:

 

http://www.e30sport.net/myths/Strutbar_Theory/strut_bar_theory.htm

 

https://www.bimmerworld.com/About-Us/is-a-strut-brace-worth-it/

 

On a 40-50 y/o unibody 02 it makes a noticeable difference in chassis rigidity that’s obviously most seen when turning at speed, but also under hard braking and when encountering bumps/potholes in straight line travel. At the least it’s a fatigue-preventative measure to keep the chassis geometry consistent..

 

On my 40 year newer 435iX, it’s a lesser overall effect since the chassis is now much more rigid.  Here it’s most detectable as improved steering response (the reduced chassis flex translates to the driver that they’re entering and transitioning turns more precisely). The front became a less floaty on rougher terrain, and is also noticeably ‘connected’ when entering/exiting steep inclines.

 

On both cars, after a bit it’ll become unnoticeable - until you remove it and drive around - then you want to immediately add it back.

 

 

 

[Lorin]

Paging Toby. 

[02Les]

Ha, I bought the same (or very similar) one in the video for the Beater several years ago. Cost all of $30 inc shipping from China and is really very useful for holding up various hoses that have a tendency to pfaff about under the hood when driving hard.

 

Edited December 5, 2022 by 02Les

[d.hitchcock]

I agree with the comments about adding rigidity to a 40-plus year-old chassis. I think it helps. I have had them (front & rear) on both of my bimmer autocross cars, and now on my 02.

[Conserv]

Jim,

 

I’ve never used a front strut brace — or a rear “upper shock mount” brace for that matter — so I’m probably not an advocate for a brace of any sort.

 

But… I’ll freely admit that my ‘02’s have always evidenced measurable flex of their nose sheetmetal in the form of ever-changing wrinkles where the radiator support’s upper flange meets the inner fenders.

 

It has been suggested that this may be caused by incorrectly aligned hoods, but this flex has been visible on the four ‘02’s I’ve owned and regularly driven.

 

Best regards,

 

Steve

 

 

[jimk]

I think it's more the up force loading that makes the corners of the front structure buckle in the corners.  The up forces from a larger anti-sway bar adds to the loading at the front tips of the subframe and frame rails.

 

Also there seems to be a bit of hacking on the front structure around the radiator in many cases that weakens the truss capability of the structure.

 

The dissertation by the Phd was hard to follow with all the huckster stuff injected.  It would have been better if it was pure analysis.

[Mark92131]

Chassis flex is a real issue when you don't have a roof.  There was a noticeable improvement to the handling when I added a front strut bar to my Cab.

 

Mark92131

 

 

[SydneyTii]

2 hours ago, Mark92131 said:

Chassis flex is a real issue when you don't have a roof.  There was a noticeable improvement to the handling when I added a front strut bar to my Cab.

 

Mark92131

 

 

You had me at Baur cab😜