Strut Braces

[ashbandicoot]

A kit car manufacturer that uses the Z3 as a base has started to sell strut braces starting with a brace for the rear strut towers - details here - www.bertinigt25.com/z3-braces.html

No affiliation

Cheers

Ash

[cngizbleevng]

Interesting. I'd like to see photos of it installed.

[BenFenner]

Kind of hard to have a rear strut brace without rear struts.


(Fully comprehending that fact will help one realize how little benefit a brace like this provides.)

[misterTT]

I got in touch with the guy behind this venture today - he says that they're a month or two out from having a lower rear brace and front brace as well, for both 4 and 6-cyl models. Once they're all available I'll probably try those two out.

Apparently the rear strut is available on eBay (US) as of today. I don't have the link, but its £114 shipped to USA.

[ashbandicoot]

[Blacklane]

I'm not sure I see the point of a rear strut brace. It would be installed at the top of the shock towers a few inches behind the big cross beam. That might stiffen the chassis a little, but not much.

Then attached to those points are rubber shock mounts connected to flexible shocks attached to pivoting Rear Trailing Arms attached to a rear subframe mounted on rubber or polyurethane. Literally everything attached to those points is flexible.

If anything, I think this might add a little weight to the rear of the car while lightening the driver's billfold.

[ashbandicoot]

I don't have one, just thought I would share, the guy's theory was it is an empty market and the butt-strut is very expensive for what it is - hence he is planning to make his own lower strut as well and market them. (Particularly if you are shipping outside US as then you have taxes etc.)

Alot of the feedback on these products can be simply placebo.. apparently It improves the looseness of the Z when cornering - I'm sure polybushing the subframe offers more than anything else

Ash

[Scarceas]

Kind of hard to have a rear strut brace without rear struts.


(Fully comprehending that fact will help one realize how little benefit a brace like this provides.)

I'm not sure I see the point of a rear strut brace. It would be installed at the top of the shock towers a few inches behind the big cross beam. That might stiffen the chassis a little, but not much.

Then attached to those points are rubber shock mounts connected to flexible shocks attached to pivoting Rear Trailing Arms attached to a rear subframe mounted on rubber or polyurethane. Literally everything attached to those points is flexible.

If anything, I think this might add a little weight to the rear of the car while lightening the driver's billfold.

It's absolutely true that there are no rear struts. So, let's agree for the purposes of this thread at least, to mentally substitute "shock tower" for "strut tower".

First I have questions about the mounting and flex concerns. I am sure we have all seen many strut tower bars that mount along the front of a car's shock/strut towers. Most of them mount to the same bolts that hold the shock/strut. These bolts pass through the towers and this locates the bar. Aren't most bushings in this application more centered around the shock shaft, and not the mounting bolts? In short, having seen Mr. Cherry's product pictures, I do not see how the mounting mechanism and presence of bushings is any different than any other similar product.

Next, despite having no actual struts, does that instantly mean that there are not similar forces at play? Additionally, there are many cars with factory double wishbones type setups that also include shock tower bars--from the factory. Are we to believe that the manufacturers are just idiots for putting a bar there, or are we to believe that there is a valid purpose, even in the absence of a strut? Let's consider these two issues for the Z3 in particular. First, I have had a hard time finding the rear upper control arm. So, when we take a corner, there should be a twisting force around the lower control arm, and no upper arm is there to help offset that force. The twisting would come mostly from momentum trying to push the car to the outside of a corner, directed through the center of the wheel. Opposing that is friction from the tire, allowing us to move in to the corner, but since the friction happens at the bottom of the wheel, there is a twisting force around the wheel. The lower arm is split to two mounting points and I am guessing that will accept most of that twisting force, but at least from my simplistic view, it would seem some of that force could also push the shock outward during a turn. If it didn't, we probably wouldn't have a need for upper shock bushings, right? The shock mounts would then transmit that outward force to the shock tower. A shock tower bar would spread some of that force to the other shock tower and reduce overall chassis flex, right? The other consideration is that we encounter vertical forces, such as a bump in the road. This pushes up on the shock, and through the shock mount, thus pushes up on the shock tower--the body of the car. I think this force is the reason that car manufacturers have seen benefit to adding a bar to a double wishbone. The bar car again spread the force, this time more vertical, across both sides of the car, still reducing overall chassis flex. Particularly in the design of Cherry's bar, note that it is not "hinged" as some strut tower bars are. This should help with the vertical forces, right?

I am not saying that I am 100% correct here, but rather, looking at it with my tiny little mind, I can see some reasons that this product may still provide a benefit despite the lack of struts and the presence of bushings.

[Dakar Ole]

No cuteee holes in carpet. Now, windshield wiper arm stress bar to reduce cowl shake, maybe.

[Vinci]

The rear shock mounts do not see side-to-side forces. The shocks are "soft-mounted" in the RSMs at the top and whatever bushing is in the lower mounting point. They are there to dampen the spring. That's all. The only forces that area of the body sees from the shock is up/down.

The front end is a completely different story, since the spring (effectively) sits between the hub and body at the upper strut mount. That makes that strut tower a major load-bearing structure and somewhat more prone to movement relative to the other side, since there is nothing in between them at the top.

The rear brace looks nice, and I think it's great that someone is making new products for the Z, but it's not going to perform a function beyond that.

[Scarceas]

The rear shock mounts do not see side-to-side forces. The shocks are "soft-mounted" in the RSMs at the top and whatever bushing is in the lower mounting point. They are there to dampen the spring. That's all. The only forces that area of the body sees from the shock is up/down.

If there are no horizontal forces, would there be a need for the shock mount bushing to surround the shock? Why even have a bushing there at all, then? Also, what benefit is there to a fully metal mount such as this:
http://store.bimmerworld.com/bimmerw...unts-p104.aspx
Also note their claim that "with the typical performance rear shock mount you are getting approximately 1/2" of uncontrolled movement as the upper shaft mount flexes".

Surely there are some horizontal forces at play?

[Blacklane]

I always thought the biggest force on top rear shock mount is the change in angle of the shock as the Rear Trailing Arms move up and down. For the same reason, the lower shock mount is a pivot that is parallel to the Trailing Arm pivots. That would make it a rotational force. That force would have little effect on handling, but would tend to fatigue metal in the shock towers leading to early failure.

[Tib]

OK where to start

In a McPherson strut setup moving the top of the strut inward or outward changes the steering geometry.(camber and toe to a much less of a degree) This is because the axle/spinal is mounted on the strut and moves in conjunction with this movement. This can be proved by swapping hats and using/installing camber plates. see exhibit A. The flex point is in the ball joint below the spinal.

Exhibit A


Now our Rear trailing arms do not change the geometry if you move the angle of the shock in any direction. The only way to change adjust camber or toe is to move the position of the rear trailing arm bushings. see exhibit B

Exhibit B



Note: The rear axle runs through the bearing in the rear trailing arm. The shock pivots top and bottom and does not effect the geometry at all.


As to the movement referred to in this statement

"Your dampers should precisely control all suspension movement, and with the typical performance rear shock mount you are getting approximately 1/2" of uncontrolled movement as the upper shaft mount flexes and moves. Average road surface imperfection rate of change means you are giving up a lot of control and potential grip. You paid for that shock - put it to work!"

It is solely talking about rebound and dampening. That would be the flex in the rubber part of this mount as the body moves up and down not side to side.


MY CONCLUSION

I do not see any way that a rear shock brace could do anything for OUR rear suspension.

- - - Updated - - -

As to the reason some manufactures add a shock/strut tower support bar to a ddb wishbone suspension:

In the photo below note that the upper wishbone is mounted to the sheet metal in the strut tower. In this case a tower support bar will minimize inward and outward movement in the tower where the upper pivot point is.



Our rear trailing arms only have 1 pivot and it relies on the 2 RTAB's to create that pivot point. The carrier bearing and axle are ridged mounted to the trailing arm, the spring provides trim height and the shock dampening.

[HeliHover]

This guy had a post with a pic anouncing the start of sales. Looks like it may have deleted?

The pic showed it mounted, looked to be right behind the seats, where there is a large piece of sheet metal running across the entire length and then the bar laying over that. ?

[Scarceas]

The pic showed it mounted, looked to be right behind the seats, where there is a large piece of sheet metal running across the entire length and then the bar laying over that. ?

I think you just won the thread.

[Tib]

its not even cosmetic unless you want to have a new item to scratch the rear window...

[felonious monk]

Interesting and looks to be well made, however, I too don't see any benefit to be gained. If anything, it will cause problems with your top/rear window if you go topless often.

[ZoO]

if in fact these add no functionality to the car, why have they made them for e36s including the compact? i guess some people just like adding things to their cars to be cool ( think honda's with c-pillar brace)

[felonious monk]

Or the butt strut... but that's a dead horse. It's your ride, your money. Do whatever you like, just don't expect everyone else to follow suit and give standing ovation.

[SounderMN]

I guess we see now why it's such an "empty market".

[Bcar]

it would stiffen the body up a bit, but not enought to notice without instrumented testing/K&C machine.

[BenFenner]

it would stiffen the body up a bit, but not enought to notice without instrumented testing/K&C machine.

The first (only so far) non-OEM owned kinematics machine has been in operation for a few years now and they still haven't found a benefit to any aftermarket strut tower brace, let alone a shock tower brace. They are like the goggles.

[Bcar]

it would stiffen the body up a bit, but not enought to notice without instrumented testing/K&C machine.

[ADAz3M]

The first (only so far) non-OEM owned kinematics machine has been in operation for a few years now and they still haven't found a benefit to any aftermarket strut tower brace, let alone a shock tower brace. They are like the goggles.

more info on this?

[BenFenner]

more info on this?

http://www.caranddriver.com/features...g-it-tech-dept

Simons adds that he’s never seen an aftermarket strut-tower brace provide a measurable handling benefit.