Anyone running a "strong-stut" or "butt-strut"?

[chrisesteschiro]

I know I'd be down for one.

[1991 318is]

Didn't people figure out that these were ineffective a long time ago? You can't tie strut towers together when you don't have strut towers. They're upper shock mounts. Lateral suspension loads in the rear are transmitted through the trailing arms to the rear suspension crossmember. Same is true even when you have rear coil overs.

[DCColegrove]

Didn't people figure out that these were ineffective a long time ago? You can't tie strut towers together when you don't have strut towers. They're upper shock mounts. Lateral suspension loads in the rear are transmitted through the trailing arms to the rear suspension crossmember. Same is true even when you have rear coil overs.

We used to think that rear braces were of no use but we were wrong. it completes the "box" that the rear sub-frame mounts to and decreases uni-body twist (doesn't necessarily work the same way as a front brace does.

Now tying the two bolts together that mount the sub frame to the uni-body...isn't that frame pretty sturdy as it stands? I'm sure it adds some weight though...

Over the past several months I've had the opportunity to put e30s on one of the big boys toys (it's nice to have friends in high places). It's called a shaker, big motherfukin machine you set a chassis on and computer controlled hydraulic rams duplicate dynamic road forces that can be measured with telemetry and laser.

You would be surprised by what flexes...and what doesn't.

[CorvallisBMW]

Didn't people figure out that these were ineffective a long time ago? You can't tie strut towers together when you don't have strut towers. They're upper shock mounts. Lateral suspension loads in the rear are transmitted through the trailing arms to the rear suspension crossmember. Same is true even when you have rear coil overs.

The idea behind this is to prevent flex within that chassis itself. By tying together the subframe bolts, the bar will reduce lateral flex in the chassis. it's just like adding an upper strut brace on the front or rear of the car. Besides, I think there is plenty of user testimony to show that they work.

[ditchdigger]

Has anyone else made their own yet? I just finished one up (excellent measurements BTW) and test fit it.

I gotta say I really do NOT like this design. The reason they use 1/2" stock is that it is an inherently weak layout. My car is lowered with IE3's and with the 1/2" spacers like they use the ground clearance is kinda scary. The spacers seem unneccesary though. I think they only exist to reinforce the area that is slotted on the end. Without them I would have almost 2 inches of clearance.

I doubt I am ever going to install this thing. I think that if the dip for exhaust clearance was centered over the exhaust side it would be much better.


I know that I can come up with something tubular that would be much stiffer, far lighter and that gives more clearance than this design. Doing this without a lift will be kinda tough though, So back to work I go.

[CorvallisBMW]

^ good to know. I've decided to make mine using a thinner bar, because it's damn hard to bend 1/2" high-grade steel. we'll see how it turns out. I suppose the possibility may be there for routing the bar above the exhaust too, but I haven't checked for clearance. I will need to investigate more.

[td325ic]

I found the instructions and hardware. Took some pics with measurements.

Photos here

All pics are high res and can be zoomed-in by clicking the magnifying glass

[CorvallisBMW]

^ you, sir, are awesome

[Justin B]

Wow, that is some seriously thick steel.

[ditchdigger]

I had to drop some things off at edge motor sports in Eugene this morning and they happened to have an E30 M3 up on the lift getting new Konis. I seized the opportunity to take some critical measurements that are mighty difficult to get in my driveway. I dug out a piece of .06 wall .75X1.5" oval tubing and got to work. This is the result




The original butt strut mounted via 1 inch of steel and a homemade "binding post" type fastener made out of a 3/4" bolt that was cut short and drilled and tapped to 14mm. That is a lot of hassle to make when an enterprising fellow could just make a mounting cup that fit into the bottom bushing retainer piece and reuse the factory nut. OK, that part was easy.



I am working under the idea that this works in compression/tension and that lateral loads aren't an issue. If that is the case then a straight piece of tubing is best but the exhaust is in the way. I just notched my way around it. I might add some extra bracing at these points.



I need to test fit it and see where it needs work. I am still unsure on how it will affect anything.

Anyway. It only weighs 2 pounds or so and gives a lot more ground clearance than the strong strut piece, It should be just as strong in tension/compression and if it hits an immovable object in the road it will bend or break instead of tear the sub frame mounts out of the unibody leaving the car permanently damaged.

[cramer]

Nice work, I like your design much better! I'm interested to see how it looks installed for clearance.

Thinking about making more of them? ;)

[TwoJ's]

Nice work. I don't know a whole lot about the loading on the sub frame while static, or under cornering load, but do you think that there would be some type of forces normal to the mount?

I think it's safe to assume that there would be some there, and in turn it would create some internal bending moments on the member. However, I think it's safe to say that they are minuscule in comparison to the compression/tension as you've said. I would just wonder about the strength vs. that flat stock piece they've made.

Regardless, it seems you've made a nice piece, and it looks like it will have better ground clearance (besides the exhaust portion). And I think you should brace it like you've shown. It would really help with rigidity under compression.

[CorvallisBMW]

^ awesome work

We ran in to the same problem with the 'binding post' type fasteners, and when we looked in to getting them from Fastenal or Oregon Bolt, they would basically increase the material cost of this thing around 400% (from around $20 to around $100), but it looks like you found a very good way around that. Congratulations.

[Kwaaahhh]

Subscribed, definitely would be interested in one for my vert! :up:

[ditchdigger]

I really only get 15-30 minutes a day to work on this and it shows. If I had a steady hour with a lift and a welder it would be done but....

Anyhow it fit but not well. So I made some changes and wound up with this. Remember that this is just tacked together to test fitment, so no cracks about the open ends and general shabbiness.



The fact that I have moved the mounting cups out of plane with the brace it has made it significantly weaker, extra bracing will fix that though.

It fit much better but still interfered with an exhaust heat shield and mounting bolt. This much was visible from the side.



After looking at how it was mounted and the new setup I can move it even further back and then up giving almost an inch more ground clearance sorta like this
:WARNING: MS paint rendering ;)


I hope to try this out tomorrow and see.