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E36/7 Z3 (1996-2002)
E36/7 Z3 Roadster, Z3 coupe, Z3 M Roadster and Z3 M Coupe talk with our gurus here.

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  #1  
Old 12-30-2004, 12:27 PM
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killeen_john killeen_john is offline
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Hypothetical Rear Strut Brace Question

My finace had purchased the IE bushings for me as a Christmas gift and I am anxiously looking forward to installing them. However, I was hoping to get into a discussion regarding the Butt Strut and whether I should continue to use it after installing the Ireland Engineering bushings.

My car is a 00' M Roadster with the H&R/Bilstein setup. Back when I added the Butt Strut, the car's handling felt better, but I can't really say that I understand why. It seems that most discussions about the Butt Strut argue that it further compresses the stock rubber subframe bushings eliminating some of their play, but that doesn't seem to be a possible explanation to me. The stock rubber subframe bushings contain a metal sleeve that should prevent the subframe support brackets from squeezing the bushings any further with or without the use of the Butt Strut. So, what exactly does the Butt Strut do?

I read a Strong Strut customer testimonial where an owner accidentally torqued the Butt Strut down with one side of the car jacked up. The end result was that the door would not close properly until after the brace bolts were loosened and retorqued with the car level on the ground. Does this mean that the Butt Strut increases torsional rigidity? From the above description, it sure sounds like there may be some other frame movement occurring back there that stiffer bushings alone can not address.

Does the stiffer polyurethane connection between the body and subframe allow the subframe as a structure to reinforce the body? In other words... does the subframe effectively become a brace for the body?

Believe me when I say that my car's limited ground clearance is enough of a reason to remove the Butt Strut brace, but I still want to know what effect it really has on the chasis. Would you leave the brace on after installing the IE bushings? Has anubody experimented with the brace on/off after installing the IE bushings?
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Last edited by killeen_john; 12-30-2004 at 12:40 PM.
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  #2  
Old 12-30-2004, 01:03 PM
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fpa1974 fpa1974 is offline
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Personal opinion here too. I feel that the butt strut contributed to a better feel. I am also getting ready to install the IE bushings and I have no plans on removing the butt strut. Clearance is not a big issue for me here since roads are pretty decent, and I did not drop the car too much with the TCK setup that I have.

Florian
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  #3  
Old 12-30-2004, 01:36 PM
wernst wernst is offline
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I have a full butt strutt/body brace installation, and will leave them there when the new bushings go on (hopefully in January.)

The Butt Strutt is really to keep the bolts the subframe is mounted to parallel to each other at all times, so that the body panels the bolts are mounted to resist flexing, and therefore reducing different toe-in angles on the two rear wheels when you encounter a bump during a corner.

The subframe is still free to move around on the now-more-stationary bolts because of the flexible rubber bushings.

I hope that made sense...

-Warr
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  #4  
Old 12-30-2004, 02:01 PM
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rjcoston rjcoston is offline
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I also have the butt strut/body brace installed, but don't have the IE bushings at this point. It appears to me that previously the butt strut alone helped to contribute to a slight improvement in the rigidity of the body. Even if I get the IE bushings installed, I would definitely reinstall the butt strut if for no other reason than the fact that it is needed to attach the runners of the body brace.

Last edited by rjcoston; 12-30-2004 at 05:30 PM.
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  #5  
Old 12-30-2004, 02:31 PM
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CarlM CarlM is offline
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If you decide to delete the butt strut let me know I would be interested in taking it off you hands and to free up more of your garage space . For a fair price of course!
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  #6  
Old 12-30-2004, 09:19 PM
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Ron Stygar Ron Stygar is offline
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Quote:
Originally Posted by killeen_john
My finace had purchased the IE bushings for me as a Christmas gift and I am anxiously looking forward to installing them. However, I was hoping to get into a discussion regarding the Butt Strut and whether I should continue to use it after installing the Ireland Engineering bushings.

My car is a 00' M Roadster with the H&R/Bilstein setup. Back when I added the Butt Strut, the car's handling felt better, but I can't really say that I understand why. It seems that most discussions about the Butt Strut argue that it further compresses the stock rubber subframe bushings eliminating some of their play, but that doesn't seem to be a possible explanation to me. The stock rubber subframe bushings contain a metal sleeve that should prevent the subframe support brackets from squeezing the bushings any further with or without the use of the Butt Strut. So, what exactly does the Butt Strut do?

I read a Strong Strut customer testimonial where an owner accidentally torqued the Butt Strut down with one side of the car jacked up. The end result was that the door would not close properly until after the brace bolts were loosened and retorqued with the car level on the ground. Does this mean that the Butt Strut increases torsional rigidity? From the above description, it sure sounds like there may be some other frame movement occurring back there that stiffer bushings alone can not address.

Does the stiffer polyurethane connection between the body and subframe allow the subframe as a structure to reinforce the body? In other words... does the subframe effectively become a brace for the body?

Believe me when I say that my car's limited ground clearance is enough of a reason to remove the Butt Strut brace, but I still want to know what effect it really has on the chasis. Would you leave the brace on after installing the IE bushings? Has anubody experimented with the brace on/off after installing the IE bushings?
I know that it's sliced bread to some.
As posted before, I have yet to understand what it does.
Before doing a mod, I think about it. If it doesn't make sense to me, I don't do it.
If it did make sense, I would not do it based on the clearance issue.
The pins to the body via the brackets are still the same interface.
If I remember right, the E30 M3 uses a reinforcement where the brackets mount.
I've heard that it is handy when swapping out the exhaust.
To me, it is just another internet truth.
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  #7  
Old 12-31-2004, 03:21 AM
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dwaynemosley dwaynemosley is offline
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I also have a butt strut. I'm not sure why it works, but it tightened up my car on bumps and curves. Definitely less squeaks and pops out of the rear.

I do know that my '03 Porsche 911 has a bar hooked across the bottom of the rear subframe mounts similar to the butt strutt. It came as the stock configuration.

An internet truth, smoke and mirrors, it's hard to tell. Maybe all this stuff is an inexact science.
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  #8  
Old 12-31-2004, 08:04 AM
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dwm dwm is offline
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I have a Butt-Strut too, but I've not noticed a big difference in driving with it on or off the car. I suspect it makes little to no difference on newer cars (I'm still under 20,000 miles).

The way the subframe mounts are done, I can see metal fatigue playing a factor over the long haul. I can post pictures if folks want, since I have a large piece of a roadster trunk in my basement that includes the subframe mounts.

On my car, clearance has never been an issue. There were (and still are) things lower than the Butt-Strut front and rear on my car.

I think the thickness of the Butt-Strut is overkill. It could be half as thick and would still be many times thicker than any of the sheet metal to which the subframe mounts are attached.

Ultimately I think it's just helping reduce metal fatigue, much the same way a front brace reduces flexing of the strut towers. But not a lot. When cornering, the load on the subframe mounts is not parallel to the Butt-Strut. Cornering loads rotate the subframe in the horizontal plane. That's why the Ireland subframe bushings make such a big difference (much more than the Butt-Strut in the handling department); they significantly reduce this rotation and the resulting rear steer.
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  #9  
Old 12-31-2004, 11:41 AM
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bob lindquist bob lindquist is offline
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  #10  
Old 12-31-2004, 12:53 PM
mzinred mzinred is offline
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butt strut

Quote:
Originally Posted by killeen_john
My finace had purchased the IE bushings for me as a Christmas gift and I am anxiously looking forward to installing them. However, I was hoping to get into a discussion regarding the Butt Strut and whether I should continue to use it after installing the Ireland Engineering bushings.

My car is a 00' M Roadster with the H&R/Bilstein setup. Back when I added the Butt Strut, the car's handling felt better, but I can't really say that I understand why. It seems that most discussions about the Butt Strut argue that it further compresses the stock rubber subframe bushings eliminating some of their play, but that doesn't seem to be a possible explanation to me. The stock rubber subframe bushings contain a metal sleeve that should prevent the subframe support brackets from squeezing the bushings any further with or without the use of the Butt Strut. So, what exactly does the Butt Strut do?

I read a Strong Strut customer testimonial where an owner accidentally torqued the Butt Strut down with one side of the car jacked up. The end result was that the door would not close properly until after the brace bolts were loosened and retorqued with the car level on the ground. Does this mean that the Butt Strut increases torsional rigidity? From the above description, it sure sounds like there may be some other frame movement "occurring back there that stiffer bushings alone can not address.

Does the stiffer polyurethane connection between the body and subframe allow the subframe as a structure to reinforce the body? In other words... does the subframe effectively become a brace for the body?

Believe me when I say that my car's limited ground clearance is enough of a reason to remove the Butt Strut brace, but I still want to know what effect it really has on the chasis. Would you leave the brace on after installing the IE bushings? Has anubody experimented with the brace on/off after installing the IE bushings?
"the Butt Strut increases torsional rigidity" Yes, exactly what it does.
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