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      10-29-2011, 01:14 PM   #23
Finnegan
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Quote:
Originally Posted by CJW2OO4 View Post
I may be interested in this or the other numerous strut bars members will be selling once they get theirs
^
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      10-29-2011, 01:48 PM   #24
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Quote:
Originally Posted by johanness View Post
Um, the point of a GB is to be less than the advertised price. OP said "The non- group buy price should be very similar to the E46 bar."
I doubt it will be below $300 even with a GB(especially the aluminum version)....
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      10-29-2011, 02:48 PM   #25
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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.
very good post :-)
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      10-29-2011, 03:04 PM   #26
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Quote:
Originally Posted by aerobod View Post
So, a few thoughts about strut braces in general on the Z4...
Thank you for the write-up. This is the type of information that really benefits the community and promotes good discussion!
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      10-29-2011, 03:35 PM   #27
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Quote:
Originally Posted by aerobod View Post
I would say the OEM brace would probablyincur closer to a 0.05mm length change in the same circumstances,
By those 'calculations', it flexes 0.024 less than the OEM version. So it represents an increase in rigidity AND looks pimp. Still in!
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      10-29-2011, 04:05 PM   #28
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Quote:
Originally Posted by johanness View Post
By those 'calculations', it flexes 0.024 less than the OEM version. So it represents an increase in rigidity AND looks pimp. Still in!
I agreed. The struts brace is mostly for look on our cars especially if it is your DD. You might "feel" increase in rigidity on the tracks or autocross (pushing it hard).
I am not sure if the info is correct here but the Z4M is one of the most rigid production car out there.
http://forums.bimmerforums.com/forum....php?t=1725881
Either way, for a few hundred bucks i might install it on my Z4MC for the pimp and placebo affects
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      10-31-2011, 05:14 AM   #29
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too bad, just bought the OEM brace
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      10-31-2011, 08:50 PM   #30
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Quote:
Originally Posted by SmartBastard View Post
too bad, just bought the OEM brace
Don't feel so bad. OE fit and finish is always nice
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      10-31-2011, 10:14 PM   #31
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Hey guys!

I am going to make this short and sweet since the snow storm this weekend knocked out our Internet/ power. So I am reduced to my iPhone.

There were some questions before in regards to price. As stated in the first post retail will be very close to the e46 race brace. The e46 race brace goes for $315 so expect something in the ball park of that price. As soon as I have an exact price I will let everyone know.

Although I really like the oem brace, the reason I always wanted this brace is due the cracking issues I have read about when the oem brace is on a hard driven car. Due to the oem brace's base plates being a cast part they simply do not have the same material strength at the RE brace. If you search the Bimmer forums track section or m3 forum you can find multiple instances of this happening.
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      10-31-2011, 11:43 PM   #32
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Quote:
Originally Posted by F360C View Post
Although I really like the oem brace, the reason I always wanted this brace is due the cracking issues I have read about when the oem brace is on a hard driven car. Due to the oem brace's base plates being a cast part they simply do not have the same material strength at the RE brace. If you search the Bimmer forums track section or m3 forum you can find multiple instances of this happening.
Good info. I did not know that
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      11-01-2011, 05:37 AM   #33
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Quote:
Originally Posted by mfanatic325 View Post
Good info. I did not know that
mines taken a serious beating for YEARS and is in perfect shape :-)
i can honestly say, if its not broke, dont fix it!! :-) Re bar looks amazing for sure, if my oe bar snaps then im all in, until then im happy :-)
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      11-01-2011, 08:32 AM   #34
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like the profile and clearance - looks OEM - if the price is right i am in!
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      11-01-2011, 10:38 AM   #35
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In relation to the fact that it takes 32,000Nm of force to deflect the chassis 1 degrees, how does that 0.026mm of deflection compare in the overall picture?
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      11-02-2011, 12:19 AM   #36
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Quote:
Originally Posted by The HACK View Post
In relation to the fact that it takes 32,000Nm of force to deflect the chassis 1 degrees, how does that 0.026mm of deflection compare in the overall picture?
The 0.026mm strut bar deflection is just an indication of the difference in the movement of the top of the strut towers relative to each other when experiencing a maximum suspension load, it doesn't give an indication of the overall increase in chassis rigidity. A complete stress model of the structure would be required to give any accurate indication of the overall rigidity change.

If the whole structure was as stiff in all directions as the strut bar (which we are only looking at for axial stiffness, as it is quite weak in other directions), then we would have an equivalent stiffness of 340,000Nm. The problem is that the strut bar is just transferring load from one strut tower to the other, so has a much more limited effect on overall stiffness - this is analogous to joining two mounds of jello with a popsicle stick, the jello doesn't become appreciably stiffer overall.
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      11-02-2011, 01:16 AM   #37
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With the difference of adding any strut bar in question, the difference between strut bars is going to be super negligible.

I had this bar on my first S2000. This thing was totally worth it.

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      11-02-2011, 03:53 AM   #38
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Quote:
Originally Posted by wyatth View Post
With the difference of adding any strut bar in question, the difference between strut bars is going to be super negligible.

I had this bar on my first S2000. This thing was totally worth it.


now thats whats im talking about!!! Get rid of the 2 hinge sections and your really talking here, bracing both top and bottom sections together rigidly would make a decent difference :-) the only problem i see with that is the 2 hinge pieces probably render this useless, make that one solid bar and you'd have one of the best strut braces ive seen....
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      11-02-2011, 12:08 PM   #39
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You are probably right but I cannot say definitively since there was no solid 4 point bar to compare. But, hinge or not, 4 points are bolted down and the X piece is still going to keep all corners flexed out. It's also solid on top (no hinge at strut tower), which, at least in the S2K community, was uncommon.
The S2K is very stiff in front but I found that this bar helped with steering turn in and response. Other bars (I had a Cusco) were nothing but show.
Cheers
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      11-02-2011, 01:51 PM   #40
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S2k bar looks awesome. Looks like you can remove the X bar, and just leave it as a regular strut if you so chose.
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      11-02-2011, 02:23 PM   #41
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Quote:
Originally Posted by Beedub View Post
mines taken a serious beating for YEARS and is in perfect shape :-)
i can honestly say, if its not broke, dont fix it!! :-) Re bar looks amazing for sure, if my oe bar snaps then im all in, until then im happy :-)
me 2.
Mine is painted to match the firewall braces pretty well
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      11-02-2011, 02:30 PM   #42
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Quote:
Originally Posted by mfanatic325 View Post
me 2.
Mine is painted to match the firewall braces pretty well
thats looks sick painted black!!!!
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      11-02-2011, 11:11 PM   #43
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thats looks sick painted black!!!!
hehehe
I didn't want the stock silver to stick out like sore thumb
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      12-04-2011, 12:43 AM   #44
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any news?
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