Parallel control arms aren't necessarily optimal. On an e30, unless you lower the center of gravity significantly by lowering the engine or other unrealistic things, you want the control arms to be slightly like this / \ for the front control arms at least, the rear semi-trailing arms may be a different story as I haven't done any kinematics calculations with them yet. One would have to do their own CG and roll center calculations to determine what ride height allows the CG to be the lowest while keeping the roll center as close as possible to the CG.
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The engineers at BMW knew how to design the suspension so it would perform optimally under all conditions the car was produced to face.
Now, two questions:
(1) Are you German?
(2) Are you an engineer?
If you answer "no" to either of these questions, you should consult someone who is and get their professional opinion.
(I have a friend who was born in Germany and knows engineering, so I'm set.)1974.5 Jensen Healey : 2003 330i/5
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Downsides:
1: More extreme CV joint angles - results in slightly less efficiency and faster wear
2: Harsher ride - I don't wanna hear about how 600 lb rate GC's actually ride like stock.
3: Worse tire wear - if camber, etc. is not corrected.
4: Snow clearance - may not matter to some
5: Scraping when pulling into steep driveways - hazardous to front air dam"I think we consider too much the good luck of the early bird and not enough the bad luck of the early worm."
-Franklin D. Roosevelt
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Originally posted by shiboujin View PostA tubular front subframe wouldn't solve any bump steer problems, there isn't any space to raise the front subframe so there isn't anywhere to go. I want people to make RCA kits and bump steer kits for our cars :(
Originally posted by shiboujinYou mean a noticeable amount of bump steer :). You might if you autox heavily and have cut springs or something. Bump steer really manifests on harsh transitions or high suspension movements. 95% of the people on these boards wouldn't notice it if it happened or don't track their car. In which case, bump steer will almost never be an issue.
as far as control arms pointing up/down vs camber curves, you have to compress the struts quite far to actually lose camber. on a lowered car with stiff springs, it's not going to compress a whole lot. I don't know about the effects on other things though.
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Pretty much what I had figured. My control arms are damn near obtuse to the ground.
"Its preparations are concealed, not published. Its mistakes are buried not headlined. Its dissenters are silenced, not praised. No expenditure is questioned, no rumor is printed, no secret is revealed."
John F. Kennedy
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Originally posted by Sagaris View PostParallel control arms aren't necessarily optimal. On an e30, unless you lower the center of gravity significantly by lowering the engine or other unrealistic things, you want the control arms to be slightly like this / \ for the front control arms at least, the rear semi-trailing arms may be a different story as I haven't done any kinematics calculations with them yet. One would have to do their own CG and roll center calculations to determine what ride height allows the CG to be the lowest while keeping the roll center as close as possible to the CG.
Originally posted by Ryan...It now emits a beautiful blue-ish yellow/green smoke from the exhaust?? No idea what would cause that color, but I assume its good.
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Originally posted by Brandon12V View PostThis. on an optimal set-up your control arms should be parallel with the ground, THROUGH a turn, with the center gravity a stock set-up has. when I first considered lowering my mkIV jetta, I found that it made the control arms sit like this \ /. Thus, creating a suspension that handles like shit. I later found out that the only way to make one handle better was to actually raise the vehicle slightly. Most mkIV guys never gave a shit about that, though. I know we're talking e30's here so no one needs to be a smart ass. Just giving an example. Low is not a bad thing, but precauations need to be taken if you still want the car to handle as good or better than stock. That said, you can easily get away with a cup kit. Slamming an e30 does things you don't want to happen unless you address the issues.... but it can be done right.
I mean seriously, strut housings, struts, and coil springs both front and rear for 300 dollars? That shit must be made out of fucking plastic.
"Its preparations are concealed, not published. Its mistakes are buried not headlined. Its dissenters are silenced, not praised. No expenditure is questioned, no rumor is printed, no secret is revealed."
John F. Kennedy
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lol so true. Back when I had one, there was only one company that had coilover made to better the suspension. I don't remember their name but the setup raised a mkIV .08"-1.2". The only option to fix the suspension geometry, when lowering it, was go with different spindles. I can't remember but I think it was 20squared tuning or USRT that offered this option.
Edit: it's H2 sport spindles.
Originally posted by Ryan...It now emits a beautiful blue-ish yellow/green smoke from the exhaust?? No idea what would cause that color, but I assume its good.
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I can't get to work or home with lowered sus. speedbumps, train tracks, other BS on the road. Tape some cardboard on your crossmember or oil pan 2-3 " long simulating where your car would be clearance wise if lowered, if that scrapes on your usual roads then your options would be lower but but big tires and wheels for clearance from the ground. Remember Verts. have special springs stock. Somewhere there's a vert spring thread.
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Since you have a convertible the geometry is slightly different from a normal hard top. If you use normal e30 lowering springs it’s going to you about 2-3 degrees of more camber in the rear than a hardtop. So to do it right you don't want to go too low and you want your shocks to match. I’m sitting on Dinan springs and Koni single adjustable shocks and I have a camber correction in the back at the moment and GC camber correction for the fronts waiting in the box at home.
Also remember you chassis is SOFT, there is a ton of flex at the doors. So you can only do so much before that softness neglects any other improvements. Welding in a cage at the point is the only other option.
Optimal suspension is:
HR-50407 H&R sport springs for convertible so it sits higher in the back.(no butt sag)
koni yellows (my pref) or billie sports.
Rear weld in camber correction
New front control arms + full tie-rod replacement.
25mm/22mm sway bars.
At this point there is enough play in the suspension for you not to get wheel hop or slam your oil pan, but not too soft to get body roll or sloppy handling. And your geometry should be spot on with -3 degrees in back and -.5 up front.
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Originally posted by Cabriolet View PostSince you have a convertible the geometry is slightly different from a normal hard top.
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Originally posted by nando View Postno it isn't. the suspension is exactly the same -the only difference is cabby's get slightly stiffer springs because they are heavier. there is no geometry change. there are only standard E30s, M3's, and ix's.
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