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Discussion Starter · #1 ·
I drive a 2001 330Ci on Bc racing Br coilovers.

I got into an accident 6 months ago that bent the front driver's side control arm, broke the tie rod and cracked the read passenger side upper control arm. I've replaced all the parts that appeared to be broken but even still the rear passenger side ride height needs to be set about an inch lower than the driver's side to be level, and I'll spin that tire on dry pavement making right turns, and even sometimes from stoplights going straight with as low as half throttle in first (i'm on 9in wide sticky tires) When I brake hard, the front driver's side is always the first wheel to lock up. I've tried switching the rear springs but the problem is still there.

Any ideas why I could be missing traction on the rear pass. wheel? Nothing seems to be bent. I thought it might have something to do with balancing (because the tire on the opposite corner locks first under braking eg. experiences higher load under braking?)
 

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Discussion Starter · #4 ·
I did a DIY alignment, but I've been meaning to spend some more time dialing it in before summer hits for autox.
 

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I was thinking a proper alignment would confirm that there is no further damage. It might not be obvious.
you might want to remove the rear shock and see if it was damaged. Sounds like you took a good whack.
 

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I used to develop vehicles for a living. One of the tools nobody has outside of a billion dollar test facility is a dynamic multipoint scale embedded into a track surface, which we used to measure weight transfer while braking, cornering etc. Based on what I learned there, and your comments, it sounds like you have the weight on the 4 contact patches way off from the balance that BMW painstakingly built into the chassis with their factory springs, suspension geometry, etc. It's one of the dirty little secrets that tuners with aftermarket suspensions and the like often create a vehicle with poor handling because they don't have the tools to build a spring and shock assembly properly mated to the vehicle. Yes, I have seen the same ads, and the same forum posts about "my new coilover suspension makes my Zoomster handle SOOOO much better, dudes!". But I'l bet the title to my E46 that if you lined up 10 internet tuner E46's against mine and did a full track evaluation (emergency braking, emergency evasive maneuvers, wet road, rough pothole handling circuit, max GVW handling, etc) that BMW's totally stock vehicle would beat all of them. Just in case you missed that - all of them. Sure, each would dominate a certain category and I'll even guess it will be the "lightly loaded dry track steady state curve max G test".

Anyhow back to you. I think you have different weights on the rear contact patches. It doesn't take much at all because the formula for calculating the traction available to a contact patch is mostly from downforce - a direct correlation. Since your vehicle is on springs, what you do at one corner affects not only the other corner on the same axle (wheelspin) the opposite corner (braking), and the same side other axle. In other words, add 10 lbs to your problem corner and the downforce came from some other corner. If you're buying super uber cool internet kits, you're paying for ads in "Super Import Tuner" magazine with a hot blonde, the salaries of the tuner's social media influencers who get checks to talk up their kits on forums like this (even though in real life they're a middle aged lady who drives a 9 year old Hyundai Elantra that smokes a little on startup), and you're paying for the hot colored anodizing on the bits. But you're not paying for a product that is "better" than the original BMW factory tuned suspension. Unless you always do "lightly loaded, dry track sunny day steady state curve max G" driving. In which case you got your money's worth.

So, find a way to get the downforce adjusted equally left to right at least on those rear wheels. Then chase alignment. A crooked rear tire will also break loose more easily with applied torque than one straight ahead, so if the other side is straight ahead then you start to see where this goes...
 

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What he said. I think its hard to improve on the factory sport suspension and decent HP tires for all around day to day performance.
 

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'01 320Ci manual
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I used to develop vehicles for a living. One of the tools nobody has outside of a billion dollar test facility is a dynamic multipoint scale embedded into a track surface, which we used to measure weight transfer while braking, cornering etc. Based on what I learned there, and your comments, it sounds like you have the weight on the 4 contact patches way off from the balance that BMW painstakingly built into the chassis with their factory springs, suspension geometry, etc. It's one of the dirty little secrets that tuners with aftermarket suspensions and the like often create a vehicle with poor handling because they don't have the tools to build a spring and shock assembly properly mated to the vehicle. Yes, I have seen the same ads, and the same forum posts about "my new coilover suspension makes my Zoomster handle SOOOO much better, dudes!". But I'l bet the title to my E46 that if you lined up 10 internet tuner E46's against mine and did a full track evaluation (emergency braking, emergency evasive maneuvers, wet road, rough pothole handling circuit, max GVW handling, etc) that BMW's totally stock vehicle would beat all of them. Just in case you missed that - all of them. Sure, each would dominate a certain category and I'll even guess it will be the "lightly loaded dry track steady state curve max G test".

Anyhow back to you. I think you have different weights on the rear contact patches. It doesn't take much at all because the formula for calculating the traction available to a contact patch is mostly from downforce - a direct correlation. Since your vehicle is on springs, what you do at one corner affects not only the other corner on the same axle (wheelspin) the opposite corner (braking), and the same side other axle. In other words, add 10 lbs to your problem corner and the downforce came from some other corner. If you're buying super uber cool internet kits, you're paying for ads in "Super Import Tuner" magazine with a hot blonde, the salaries of the tuner's social media influencers who get checks to talk up their kits on forums like this (even though in real life they're a middle aged lady who drives a 9 year old Hyundai Elantra that smokes a little on startup), and you're paying for the hot colored anodizing on the bits. But you're not paying for a product that is "better" than the original BMW factory tuned suspension. Unless you always do "lightly loaded, dry track sunny day steady state curve max G" driving. In which case you got your money's worth.

So, find a way to get the downforce adjusted equally left to right at least on those rear wheels. Then chase alignment. A crooked rear tire will also break loose more easily with applied torque than one straight ahead, so if the other side is straight ahead then you start to see where this goes...

I agree with the things you consider as variables and the tuner bit philosophy (it takes a very keen eye to disguise between real race equipment and boy race anodized parts)and yes the steady state g numbers are overplayed cause simply there aren't usually any steady state situations in driving , but I doubt downforce is his problem.probably something messed up with the alignment would be my guess ,perhaps a sudden non ideal dynamic camber change :)
front driver / rear passenger situation indicates a problem with this weight transfer crossloading senario .
 

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With respect to the suggestion that wheel loading might be an issue, OP did say that one side had to be set differently than the other by an inch. Granted, several possible explanations, but perhaps worth pondering. I'd start with alignment and search for more damage. Including the shock.
 

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'01 320Ci manual
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With respect to the suggestion that wheel loading might be an issue, OP did say that one side had to be set differently than the other by an inch. Granted, several possible explanations, but perhaps worth pondering. I'd start with alignment and search for more damage. Including the shock.
Of course that, the most obvious things are the ones to check, like differences from one side to other, alignment, broken bent parts, a blown shock maybe (internally damaged)
 

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Discussion Starter · #12 · (Edited)
It's not an issue with any of the aftermarket parts I've installed. The aftermarket shocks and springs are the same left and right and I've switched the sides but the issue remains. It seems like the control arms and the axle just sit farther from the body (even with adjustable spring perches at same settings and shocks not bolted [eg. at full droop] to the knuckle the rear pass. side droops down further, when the swaybar hits either the lower control arm or the axle it's still about 5-10cm away from contacting on the other side.)

It seems like the suspension geometry doesn't behave the same left to right but there doesn't appear to be any broken parts (ex. subframe looks totally fine). I switched the rear tires to check if it was a wear issue but the issue is still there.

no wheel hop, the shock is fairly new and there's no leak so I doubt that's the issue. I also checked the ride height without the shocks bolted on and the ride height difference is the same
 

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May you have a torn apart rear subframe floor? Or a bent rear camber arm? also , I wouldn't jump in the conclusion that the control arms are more far of the body using the roll bar as a reference point , cause the bar can slide through its mounting bushings
 

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Drop the the front subframe and make sure nothing is bent . I'd also replace the entire front suspension and wheels if the accident was bad. Also a proper alignment is important. Lots of places have lifetime alignments so maybe get one first and see what they say.
 

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Parts and/or their mounting points can be bent, and it may not be obvious to the naked eye. The alignment may point you to problem areas. I'd be driving carefully.
I've seen shocks that didn't leak that had no rebound. Or very sluggish. Just saying.
 

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LF locks up first
RR spins
You need to corner balance the car.
If you don***8217;t have access to scales just start by raising either corner with no grip.
 
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