[TSM330i]

I was looking into Intrax coil-overs for a Z4 race car build, but they are using a true coil-over so it would not be legal for BMWCCA events.

Here is the link to e9X applications from Intrax:
http://www.intraxracing.nl/?cat=prod...M3_dampers_1K2

The BMW Motorsports team uses them on the new Z4 GT3.

[turugara]

Originally Posted by TSM330i

I was looking into Intrax coil-overs for a Z4 race car build, but they are using a true coil-over so it would not be legal for BMWCCA events.

Here is the link to e9X applications from Intrax:
http://www.intraxracing.nl/?cat=prod...M3_dampers_1K2

The BMW Motorsports team uses them on the new Z4 GT3.

What I would give to have a Z4 GT3 with the S65 and that kit.

[TSM330i]

Originally Posted by turugara

What I would give to have a Z4 GT3 with the S65 and that kit.

About 340,000 Euros ($434,000)!

http://www.bmw-motorsport.com/en/cars/bmw-z4-gt3.html

[techwhiz]

One of the big issues with e36 (used to have one) and e46 cars is the sheet metal for the rear shock mount. There is no reinforcement. On the convertibles there was an additional plate that can go on top of the sheet metal and create a sandwich of the flimsy body metal.

not sure what my e90 looks like, but based on my experience with e30 and e36 cars I wouldn't do anything without reinforcing where the RSM bolts up.

[bbnks2]

Anyone reading this in 2018 should ignore everything said. It is pretty much all wrong. There are few, if any, benefits to moving to a rear coil-over. The only noticeable benefit would if it was easier to adjust/maintain and I don't even see that. One relatively insignificant benefit would be less bowing of the spring... but that is so negligible it's not even worth mentioning despite high markup coil-overs trying to pedal that as an excuse to do the conversion..

The upper strut mount is very weak as is, and a coil-over setup would not decrease stress on the sub-frame. That makes 0 sense.

[feuer]

Struts/shocks and springs perform better when placed further away form the center line of the vehicle. Example of this is modern pickup trucks moving them outside of the frame vs old fashion designs that had them inside of the frame. Regarding increase or decrease stress on the subframe won't be any. The stress will be on the chassis. e36/46 are experiencing lot more stress on the chassis because the mounting points were inside of the chassis and close to each other so to subrame is ripping the floor up. So if you move the spring away on e36/46 you are reducing the stress on the chassis. On e90 the mounting points are right on the chassis so that is not a issue. Shock tower would have to be reinforced on all e36/46/90. Im not familar with e30. Never owned nor mod one.

[Cloud9blue]

Originally Posted by feuer

Struts/shocks and springs perform better when placed further away form the center line of the vehicle. Example of this is modern pickup trucks moving them outside of the frame vs old fashion designs that had them inside of the frame. Regarding increase or decrease stress on the subframe won't be any. The stress will be on the chassis. e36/46 are experiencing lot more stress on the chassis because the mounting points were inside of the chassis and close to each other so to subrame is ripping the floor up. So if you move the spring away on e36/46 you are reducing the stress on the chassis. On e90 the mounting points are right on the chassis so that is not a issue. Shock tower would have to be reinforced on all e36/46/90. Im not familar with e30. Never owned nor mod one.

yeah, it only really benefits the shock to get some extra travel and reduce the motion ratio. For the same wheel travel, you get bigger displacement at the shocks, which should allow for better damping for our heavy chassis. The downside is potential cavitation and foaming that might occur with the shock oil, due to the increase travel rate of the piston inside of the shock. But with a modern shock design, this really isn't a problem.

For springs, the benefit is negligible. Considering the rear shock mounts were never designed for carrying the full weight of the car, I wouldn't be surprised to see some structural failure with a true coilover rear suspension on a stock unreinforced chassis.

[Emilime75]

I would think spring/shock location would certainly play a role on subframe stress, or at least the control arm mounting location. The further the suspension is away from the center of the car, the less cantilever effect that suspension has on those mounting points and the subframe itself. It's the seesaw effect...place the pivot point(lower spring/shock mount) in the center of the arm, whatever force is present to move the wheel up, has an equal force pulling inner control arm and subframe down(maybe not, due to spring/shock compliance, but you get what I mean). Place that pivot point further out, and the inner force decreases...place it further in, and it decreases...or, do I have it all wrong?

[bbnks2]

Originally Posted by Emilime75

I would think spring/shock location would certainly play a role on subframe stress, or at least the control arm mounting location. The further the suspension is away from the center of the car, the less cantilever effect that suspension has on those mounting points and the subframe itself. It's the seesaw effect...place the pivot point(lower spring/shock mount) in the center of the arm, whatever force is present to move the wheel up, has an equal force pulling inner control arm and subframe down(maybe not, due to spring/shock compliance, but you get what I mean). Place that pivot point further out, and the inner force decreases...place it further in, and it decreases...or, do I have it all wrong?

Depends on what your talking about really. I was referring to the chassis cracking that occured on the e46. The spring sits between the chassis and the lower camber arm. If the spring is mounted more inboard then it does not cause any more stress on the chassis because it doesn't travel as far for the same wheel travel as if the spring was mounted closer to the wheel. That is the motion ratio term that keeps getting tossed around and you are exempliying with the first part of your seesaw example.

Why would a 900lb spring that gets compressed 1 in put more stress on the spring perch then a 300lb spring that compresses 3in when mounted at the strut location? Both mounting points on the chassis will see the same 900lb load... However the chassis mounting point for the shock is 100% a weaker point that the stock inboard location. The e82 chassis is not prone to cracking like the e46 chassis. That cracking actually didn't have much to do with the sunframe at all... Or spring rates. The structural rigidity of the chassis itself was poor and the subframe would tear away from the chassis. Changing the spring mounting location does not change the 4 points in which the subframe attaches to the chassis nor does it change the structural integrity of the chassis at said 4 mounting points. If anything, you'd be decreasing the amount of stress on the lower camber arm eccentric bolt like you said yourself...

A lower motion ratio, and a high spring rate, just means that you'll need a bit more rebound damping as the return rate of the spring will be higher (hooks law).

The shock does not gain any travel with the m3 arms. It mounts the exact same location. The moutning poitn is just changed from a rubber mount that can deflect to a bolt through application. Again, that shock deflection is so little it means nothing for anything short of a full blown race car. Put in the slightly stiffer rubber mounts made by Monroe if you think deflection of the lower shock mount is somehow having an impact on your driving experience. Again, the upper mount is what I would be worried about.

[Emilime75]

Because, leverage, and it's change based on pivot point location. I wasn't speaking about any chasis in particular, just generalizing and not specifically to your posts, but to this thread's original question.

[bbnks2]

Originally Posted by Emilime75

Because, leverage, and it's change based on pivot point location. I wasn't speaking about any chasis in particular, just generalizing and not specifically to your posts, but to this threads original question.

Go crawl under your car and review the relationship between the chassis and the camber arm. With modest lowering mine are Parallell. When the wheel compresses the spring is leveraged LESS when it is mounted inboard vs when it is mounted outboard (closer to the wheel). In regard to the e46 again, the spring was mounted a bit closer to the wheel which made the motion ratio closer to 1:2 instead of our 1:3 yet that chassis had MORE problems.

Unless you're building a purpose built race car you won't be seeing any gains from this outside of "doing it just to do it" although it would be superior if done right.

[Emilime75]

I don't have to crawl under my car, and what I'm talking about has nothing to do with how level your camber arm may be or spring compression. Maybe you should go crawl under your car and look at where the spring and shock are mounted to the camber arm, view that as the pivot point. When the wheel moves upwards, the camber arm wants to pivot at the bottom of the spring and shock as those components resist and apply a negative force to that movement. This, in turn, puts stress on the inner portion of the camber arm, ie the bushing, and pulls downwards on the subframe, as well. Moving that pivot point further out decreases that pulling force, and can actually be completely eliminated if moved out far enough.

[bbnks2]

Originally Posted by Emilime75

I don't have to crawl under my car, and what I'm talking about has nothing to do with how level your camber arm may be or spring compression. Maybe you should go crawl under your car and look at where the spring and shock are mounted to the camber arm, view that as the pivot point. When the wheel moves upwards, the camber arm wants to pivot at the bottom of the spring and shock as those components resist and apply a negative force to that movement. This, in turn, puts stress on the inner portion of the camber arm, ie the bushing, and pulls downwards on the subframe, as well. Moving that pivot point further out decreases that pulling force, and can actually be completely eliminated if moved out far enough.

The angle of the camber arm absolutely matters. What matters most is that the wheel pivots at the camber arm eccentric on the sub-frame. No matter where you put the spring in between the wheel and the sub-frame relatively the same torque is applied to the sub-frame mount even though the leverage point changes a bit. An inboard spring is displaced LESS (motion ratio) and the is backwards due to the angle of my camber arms after lowering. It has nothing to do with the spring "pulling down" on the sub-frame anyway.

All a coil-over does for 99% of people is reduce bending moment of the spring (good but a marginal change) and moves the stress to a weaker part of the chassis (exceptionally bad).

[Emilime75]

https://goo.gl/images/x21YyV

So, you're telling me that altering dimension B has no effect on load at the inner and outer points of A?

[feuer]

Originally Posted by Emilime75

https://goo.gl/images/x21YyV

So, you're telling me that altering dimension B has no effect on load at the inner and outer points of A?

I think that bbnks2 already address that by saying that that the spring rate would have to change so the actual effect on altering dimension B will not affect the inner and outer points on A. If the spring rate remains the same then yes, you are correct. On e36/46 the stress wasn't on the subframe. The stress wasn't on the chassis either because the subframe wasn't mounted on the chassis to begin with. It was bolted between the chassis onto the floor.

[bbnks2]

Originally Posted by feuer

I think that bbnks2 already address that by saying that that the spring rate would have to change so the actual effect on altering dimension B will not affect the inner and outer points on A. If the spring rate remains the same then yes, you are correct. On e36/46 the stress wasn't on the subframe. The stress wasn't on the chassis either because the subframe wasn't mounted on the chassis to begin with. It was bolted between the chassis onto the floor.

yes and the chassis and floor pan are what would crack and tear. Thanks Feuer. I was looking into this again because I did the M3 rear end swap and was considering doing a rear coilover setup but chose to stick with the stock location and inverted dampers.

[feuer]

Originally Posted by bbnks2

yes and the chassis and floor pan are what would crack and tear. Thanks Feuer. I was looking into this again because I did the M3 rear end swap and was considering doing a rear coilover setup but chose to stick with the stock location and inverted dampers.

I have owned e36/46 cars and have experience this particular failure first hand. Welding those reinforcement plates won't help on track car with stiff suspension and sticky tires. Here you can see how need to be done in order to hold http://www.backroads.ie/forums/showt...r-cracks/page2 Also you can see how the bolts aren't on the chassis. That is why e90 doesn't have this problem. On e36/46 only the springs and the trailing arms are mounted on the chassis. The pocket for the trailing arms breaks too but that is a different issue all together.

[Cloud9blue]

Originally Posted by feuer

I have owned e36/46 cars and have experience this particular failure first hand. Welding those reinforcement plates won't help on track car with stiff suspension and sticky tires. Here you can see how need to be done in order to hold http://www.backroads.ie/forums/showt...r-cracks/page2 Also you can see how the bolts aren't on the chassis. That is why e90 doesn't have this problem. On e36/46 only the springs and the trailing arms are mounted on the chassis. The pocket for the trailing arms breaks too but that is a different issue all together.

how many forums do you visit on a daily basis? you are like a walking encyclopedia on BMW and VW cars.

[feuer]

Originally Posted by Cloud9blue

how many forums do you visit on a daily basis? you are like a walking encyclopedia on BMW and VW cars.

Probably too many. I could have gotten few online degrees with ease lol.