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      08-31-2012, 02:38 PM   #177
johanness
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Quote:
Originally Posted by XMetal
Guys

You need to realized that this may NOT be a poorly made piece. This will happen for any one-piece bar that have so many alignment holes (points) unless it's a custom made piece for that ONE particular car. There are just so many variables that can go wrong to cause it not to fit properly:
1. Build tolerances in the car.
2. Car dimensions change over time.
3. Different ages in cars.
etc...

This is why most bars out there, including OE, uses a 3-piece design to alleviate this fitment issue.

I'm sorry to say that if you want this stronger one-piece bar, it must be custom fitted.
You're exactly correct.

I fitted mine at the shop yesterday however with ZERO issues. Followed the instructions to the letter on level ground and everything lined up. Retained my camber settings (-2.5) and everything sat flush and fit. The only thing is the clearance to the hard-line (on top of the engine) being negligible. Not sure what kind of impact that's going to have in the long run, but will monitor. I'll take shots when I'm back from the long weekend. My fitment could also be because I've only got 11k on the ODO - still quite new. I expect it's the same reason I don't have 2-3mm of space under the hard line - no engine /motor mount sag.

I fully expected the intended effect of this bar to be small or muted at best (as per OEM bar). Couldn't be farther from the truth. TOTALLY tightened up the steering and front end. Never thought it would be possible on a car with a torsional rigidity of 32,000Nm.

Awesome purchase. Next rack day Sept 10.
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      11-29-2012, 04:55 PM   #178
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had to clean ICV, DISA and throttle body so a friend helped me out (I have no tools). Removed the Race Brace and re-installed correctly per RE specs...Took pictures of the work done by RRT to custom fit too. Sorry for the HUGE delay, but better late then never...


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      11-30-2012, 09:47 AM   #179
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Quote:
Originally Posted by aerobod View Post
So, a few thoughts about strut braces in general on the Z4. First, referring to the hastily sketched diagram below, there are a few structural considerations:
- A strut brace closes the triangle between the strut towers and the firewall-to-strut braces.
- Most of the problematic flex in the strut towers comes from the vertical wheel loads as the suspension is compressed due to either bumps or load transfer in cornering, this load tries to rotate the tower inwards by applying pressure to the outer point of the triangle formed by the strut, strut tower and lower control arm. The horizontal cornering loads are mainly reacted into the lower reinforcement plate, having little effect on the top of the strut tower.
- A strut brace can only really transfer loads from one strut tower to the other due to a horizontal shearing of the brace, the strut towers and the lower reinforcement. This means the added stiffness comes from making the two strut towers flex together as opposed to independently.
- In the case of the relatively thin strut brace end plates due to clearance issues, the brace can provide little resistance to bending between itself and the top of the strut tower, therefore most resistance is in the form of compressive or tension load along the brace.

Assuming a maximum state cornering situation where ther inner wheels are about to lift off the ground, the maximum load transferred into rotating the strut tower would be about 4000N (assuming about 400kg on each front wheel resolves to 800kg on the loaded wheel, 0kg on the unloaded one). As the outer lower control arm ball joint is about half the distance from the bottom of the strut as the length of the strut, this would lead to a shearing force of up to 2000N at the top of the strut tower.

This shearing force is going to be dissipated through the inner fender/frame reinforcement, triangular braces and strut brace. Assuming the elements other than the strut brace are relatively flexible (which they aren't, but we'll look at worst case), then lets take 2000N as the lateral load on the strut brace.

If we look at material properties, assume a brace length of 1m. The Rogue Engineering brace seems to weigh about 4kg for the steel version, so allow 3kg for the main brace, 1kg for the end plates (M3 brace specs). This leads to a cross-sectional area of 390mm^2. Assuming 200GPa Young's Modulus for steel and a 2000N load, we find the compression or tension in the strut at that load leads to a change of length in the strut bar of 0.026mm.

0.026mm length change is probably very small relative to the inherent flex of both strut towers, so they can effectively be seen as rigidly joined, meaning that flex of one tower can potentially be halved, due to inducing an equivalent flex in the other tower when the strut brace is in place. I would say the OEM brace would probably incur closer to a 0.05mm length change in the same circumstances, but this is still very small (leading to a camber change of about 0.006 degrees, assuming a strut length of 0.5m).

Overall I'd say the Rogue Engineering strut would look very nice especially if painted black, but would be hard pressed to see any noticeable improvement compared with the OEM one in terms of usable stiffness.
I think your load conditions are wrong. It's there to prevent torque deflections about the cars axis of travel.
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      12-01-2012, 02:33 AM   #180
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Quote:
Originally Posted by Dammmittt View Post
I think your load conditions are wrong. It's there to prevent torque deflections about the cars axis of travel.
The torque in the chassis around it's axis is still reacted to the ground via the strut towers and springs and the forces are reacted through the brace via the three mounting bolts on the top of each strut tower. So although twisting due to driveline torque or deflection due to suspension loading may both create load on the brace via the towers, the stiffening effect of the brace stays the same.
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      12-01-2012, 02:40 AM   #181
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Aerobod, I think u should install one of these and THEN share your experience. There's a distinct before/after difference. It's a great piece.
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      12-01-2012, 02:59 AM   #182
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Quote:
Originally Posted by aerobod View Post
The torque in the chassis around it's axis is still reacted to the ground via the strut towers and springs and the forces are reacted through the brace via the three mounting bolts on the top of each strut tower. So although twisting due to driveline torque or deflection due to suspension loading may both create load on the brace via the towers, the stiffening effect of the brace stays the same.
Shocks and struts dissipate the load, they don't eliminate it. I'd argue that chassis torque load during turn in/out is much higher than sheer on the crossbeam. Got some FEM software?
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      12-01-2012, 12:39 PM   #183
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Quote:
Originally Posted by Dammmittt View Post
Shocks and struts dissipate the load, they don't eliminate it. I'd argue that chassis torque load during turn in/out is much higher than sheer on the crossbeam. Got some FEM software?
I don't have any FEM software unfortunately, too much money for my budget. The shear loading I referenced in the original is in relation to the "box" made up of the strut brace, two strut towers and lower reinforcement. Chassis torque during turn-in would have the same effect on this "box" as suspension load transferred to it. The lower reinforcement and strut brace are sheared relative to each other. The original analysis was looking at the effect of strut braces of different rigidities between the towers, with the conclusion that having a strut brace gave most of the benefit, as opposed to fine tuning the lateral strength of the brace.

From a chassis rigidity perspective, triangulating from the middle of the brace to the point where the bottom of the strut tower meets with the lower reinforcement would bring great benefits but is not very practical due to the engine being in the way. From the perspective of the brace doing anything other than keeping the distance between the strut towers fairly constant, you just have to look at how easy it is to lift the free end of the brace by hand if it is only bolted to one tower, to realize it isn't much better than a pivot where it is attached to the top of the strut tower.
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      12-18-2012, 12:29 AM   #184
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Will this Racebrace fit on a non-M?
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