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Thread: E36 Roll Center Correction Experience(s)

  1. #1
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    E36 Roll Center Correction Experience(s)

    Looking for real world experiences of the various roll center correction options for the E36 chassis. Specifically interested in the Ground Control, SLR Mini and Magnus Racing (MRT) kits. Not looking at tubular control arms, just roll center and bump steer correction. Please also include front roll bar, spring and camber adjustments after the kit was installed and driving/grip impressions. This should be pretty informative for all thanks!
    Dave
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  2. #2
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    I have a version of the Ground Control setup - I only use their bearings as well as their bumpsteer kit (tie tods, etc). The spindle portion/bolt and spacer is custom. This is on a race car and honestly, I wouldn't bother for the additional complexity and maintenance involved. For the bump steer, I would check how much you are getting now in bump and droop and decide if it's worth it. I would probably do the bumpsteer over the roll center and just keep the front control arms at a reasonable angle. 650 front springs with 28mm roll bar. Car weighs @2750 with driver.

  3. #3
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    I currently have the mini SLR kit on my E36 Coupe Autocross car. Ran it with 275/35-17 Hoosier A7s on 17x10.5 rims all around. 800lb front springs with 900lb rear and no rear bar. Have the GC small front bar, adjusted to about 2 1/2” from the end of the bar, and attached to the LCA.

    I do not have enough front bar. The inside rear tire gets up in the air a lot and I often feel like I have a lot of mid corner understeer. The small front bar (.120” wall) has a calculated rate of about 280in/lbs. The H&R 28mm bar has something like 430ish in/lbs. I asked GC to make me a custom large (.188” wall). That one calculates to about 407, which in light of my 28mm of roll center correction from my SLR kit should put me right in the sweet spot.

    And I’m at 4 degrees neg camber in the front with 2.5-2.8 rear. I also have the Z3 steering rack and that combined with the SLR steering tie rod relocation makes the steering fast enough that I almost NEVER need more than 90 degrees of steering wheel turn in either direction to navigate the Autocross course.
    Last edited by jakermac; 04-27-2019 at 12:26 AM.

  4. #4
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    If you google it, you'll find lots of diagrams on rollcenter correction for strut cars. The center of the outer balljoint should be near the height of the center of the inner. Takes a little work, but you can closely (not perfectly) measure both with the car on the ground.

    I tried the GC rollcenter kit, along with their bumpsteer kit. I'm a believer in the idea, but they don't give much assistance of exactly how much spacer you want and where. I just used all the spacers I could until I ran out of a comfortable enough number of threads for the bottom nut.

    While the GC kit did correct a little bit of the difference in heights, it did not go far enough to make much difference. If you look at say the SLR kit, you'll see a ton of correction at the outer balljoint (distance between bottom of upright and center of balljoint). The GC can get no where near that much distance. I think I got 12mm or so correction, and you need about 3x that much.

    I'm trying another vendors product now, I'll have to report back as I haven't been on the track with it yet.

    As someone said above, you absolutely must do bumpsteer if you change RC - so start with a bumpsteer kit (GC or AKG) and buy a gauge or pay someone to set up bump for you.

    The reason for RC correction is to slow the crazy camber gain of lowered strut cars. The current bandaid is a really big sway bar, so if you do decide to fix the RC, be prepared to change front springs or bars, and work on setup again.

    It's not for the faint of heart - definitely not a throw it on and forget it sort of mod. That said, it's definitely worth some lap time, assuming you have the patience and will to also change front roll stiffness (less is needed).
    Last edited by CoMZ302; 04-09-2019 at 05:29 PM.
    2002 BMW M Roaster.
    1998 BMW 328is SCCA E Production road racer.

  5. #5
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    Quote Originally Posted by jonb94118 View Post
    I have a version of the Ground Control setup - I only use their bearings as well as their bumpsteer kit (tie tods, etc). The spindle portion/bolt and spacer is custom. This is on a race car and honestly, I wouldn't bother for the additional complexity and maintenance involved. For the bump steer, I would check how much you are getting now in bump and droop and decide if it's worth it. I would probably do the bumpsteer over the roll center and just keep the front control arms at a reasonable angle. 650 front springs with 28mm roll bar. Car weighs @2750 with driver.
    Thanks for the info! You're a tad lighter than me but rates sound similar (650/800 on AST singles).


    Quote Originally Posted by jakermac View Post
    I currently have the mini SLR kit on my E36 Coupe Autocross car. Ran it with 275/35-17 Hoosier A7s on 17x10.5 rims all around. 800lb front springs with 900lb rear and no rear bar. Have the GC small front bar, adjusted to about 2 1/2” from the end of the bar, and attached to the LCA.

    I do not have enough front bar. The inside rear tire gets up in the air a lot and I often feel like I have a lot of min corner understeer. The small front bar (.120” wall) has a calculated rate of about 280in/lbs. The H&R 28mm bar has something like 430ish in/lbs. I asked GC to make me a custom large (.188” wall). That one calculates to about 407, which in light of my 28mm of roll center correction from my SLR kit should put me right in the sweet spot.

    And I’m at 4 degrees neg camber in the front with 2.5-2.8 rear. I also have the Z3 steering rack and that combined with the SLR steering tie rod relocation makes the steering fast enough that I almost NEVER need more than 90 degrees of steering wheel turn in either direction to navigate the Autocross course.
    You're running 4 degrees front camber WITH roll correction? Interesting, I would think the car would have less front grip this way due to LESS camber loss with roll correction. I run ~3.7 front camber with GC's largest bar on 3/4 stiff now, no roll correction.


    Quote Originally Posted by CoMZ302 View Post
    If you google it, you'll find lots of diagrams on rollcenter correction for strut cars. The center of the outer balljoint should be near the height of the center of the inner. Takes a little work, but you can closely (not perfectly) measure both with the car on the ground.

    I tried the GC rollcenter kit, along with their bumpsteer kit. I'm a believer in the idea, but they don't give much assistance of exactly how much spacer you want and where. I just used all the spacers I could until I ran out of a comfortable enough number of threads for the bottom nut.

    While the GC kit did correct a little bit of the difference in heights, it did not go far enough to make much difference. If you look at say the SLR kit, you'll see a ton of correction at the outer balljoint (distance between bottom of upright and center of balljoint). The GC can get no where near that much distance. I think I got 12mm or so correction, and you need about 3x that much.

    I'm trying another vendors product now, I'll have to report back as I haven't been on the track with it yet.

    As someone said above, you absolutely must do bumpsteer if you change RC - so start with a bumpsteer kit (GC or AKG) and buy a gauge or pay someone to set up bump for you.

    The reason for RC correction is to slow the crazy camber gain of lowered strut cars. The current bandaid is a really big sway bar, so if you do decide to fix the RC, be prepared to change front springs or bars, and work on setup again.

    It's not for the faint of heart - definitely not a throw it on and forget it sort of mod. That said, it's definitely worth some lap time, assuming you have the patience and will to also change front roll stiffness (less is needed).
    Thanks! I already have large and medium front GC roll bars (for swapping front spring rates). Currently running 650 front with the large bar on roughly 3/4 stiff. I am expecting the front rate to stay at 650, but hoping to go down in roll bar size with roll correction. Just trying to get an idea of how much change (grip) I can expect to add. What kit are you using? The MRT kit (32MM correction?) is very similar to SLR (28MM correction?) and looks pretty good. Thanks!
    Dave
    '18 RAM 2500 Laramie Cummins
    '15 Pure White VW Touareg TDI
    ///'95 Avus M3 S54B32 Race car -- 2022 ProAutoSports PS1 Champion
    ///'72 Chamonix 2002 (Restoration project)

  6. #6
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    Quote Originally Posted by MPWRCPE View Post
    You're running 4 degrees front camber WITH roll correction? Interesting, I would think the car would have less front grip this way due to LESS camber loss with roll correction. I run ~3.7 front camber with GC's largest bar on 3/4 stiff now, no roll correction.

    Thanks! I already have large and medium front GC roll bars (for swapping front spring rates). Currently running 650 front with the large bar on roughly 3/4 stiff. I am expecting the front rate to stay at 650, but hoping to go down in roll bar size with roll correction. Just trying to get an idea of how much change (grip) I can expect to add. What kit are you using? The MRT kit (32MM correction?) is very similar to SLR (28MM correction?) and looks pretty good. Thanks!
    The Ground Control site "used" to show 3 sizes of front bar for the E36, but they only ever had 2 sizes: .120" wall thickness and .155" wall thickness. Because the bars were designed for endlink attachment at the strut, the rates were too low for LCA attachment like the non-M E36 is designed. I asked for a custom .188" bar and waited about 8 months for the order. They MAY have brought in some extras. I'm looking forward to trying the big bar with my current alignment and camber settings. I think it'll work extremely well for my setup. Because I had "too small" a front bar in the past, I never suffered from excessive inner shoulder wear (too much camber) on either the street or the autocross course. We'll see how things go from now on. I have a little room for altering the adjustment of the bar if necessary to optimize the setup.
    Last edited by jakermac; 04-09-2019 at 08:28 PM.

  7. #7
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    Keep in mind that how much correction you 'need' will depend on how much the car is lowered. Also, the camber gain/loss isn't as drastic as many think as the wheel moves up and down. I have measured it and while I don't remember exactly, it wasn't as bad as it's made out to be. Moving the roll center upwards effectively increases the wheel rate in roll due to leverage and center of gravity. This will not necessarily increase grip, but in theory can allow the running of lower static rates in spring and bar. I run a 650 front spring rate coupled with a 900 rear mounted in OEM location. Front swaybar typically in middle or loose setting and rear (22mm) bar usually set on full stiff. 4.0 degrees camber in front, 2.7 or so in the rear. Hoosiers will still show edge wear with this front camber and I have run as much as 4.5 in the front. Maybe with more front bar I could get away with less camber, but every time I have stiffened the front bar, I have found the car to push more on entry leading to oversteer midcorner. I personally think most people run too much front rate as it feels safer/stable on entry, but it's been slower for me at least. Much depends on driver, tires, preference, dampers, rake, tracks, phase of moon, and who knows what else! Fast, sweeping corners, I don't find much difference. Tighter, slower corners with more steering input, I do think roll center correction helps on our cars, but I would not look at it as a magic pill for dramatically lowering lap times. If you are competing and looking for tenths, it's worth looking into. Otherwise, I would say save your money for tires which always make a difference.

  8. #8
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    I have the SLR mini-kit with Z3 rack. I absolutely, positively recommend doing both! It makes the car incredible to drive.

    Here is my road atlanta, you can see even on the straight away the quickness of the rack does not affect me.

    https://www.youtube.com/watch?v=Re3k-CPzoFw

  9. #9
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    Quote Originally Posted by Inflame View Post
    I have the SLR mini-kit with Z3 rack. I absolutely, positively recommend doing both! It makes the car incredible to drive.

    Here is my road atlanta, you can see even on the straight away the quickness of the rack does not affect me.

    https://www.youtube.com/watch?v=Re3k-CPzoFw
    "Don't know my lap time"

    Love it! Nice driving.

  10. #10
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    Has anyone use the MRT kit before? What are your thoughts compared to SLR?

    https://www.ebay.com/itm/BMW-E30-E36...EAAOSwKhpdijXx

  11. #11
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    I have 50mm drop knuckles on my car. its primarily used for drifting, but I drive it on the street all the time. Roll center correction is mandatory if you plan on significantly lowering the car and you should try to match level of lowering with amount of correction. Basically you want the arms and tie rods level when the cars on the ground and settled. The MRT kit looks solid and quite a bit cheaper.

  12. #12
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    I just received the MRT kit. Hope to install before first event in 2 weeks. I did receive a post from someone about earlier MRT's failing at the shaft that's inserted into the steering hub arm (I think), but supposedly that was fixed.

    FYI, there's a Turner solution now also. $700, but it's advertised to come with steering limit and and spacers to adjust bump steer. Not sure that's worth the extra $$$'s, but it's good to have choices.

    https://www.turnermotorsport.com/p-5...tion-race-kit/

  13. #13
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    Quote Originally Posted by Inflame View Post
    I have the SLR mini-kit with Z3 rack. I absolutely, positively recommend doing both! It makes the car incredible to drive.

    Here is my road atlanta, you can see even on the straight away the quickness of the rack does not affect me.

    https://www.youtube.com/watch?v=Re3k-CPzoFw
    What z3 rack specifically?

  14. #14
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    There is only one Z3 rack which is a faster steering upgrade - the non M rack. It is the same rack for all models from 96-02 except for M cars which got the slower rack.

    -Mark

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    So the Z3 non-M 6 cylinder rack is the same as the Z3 1.8 four rack?

  16. #16
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    Can someone just post up a part number? Would really simplify things.

  17. #17
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    Quote Originally Posted by lowside67 View Post
    There is only one Z3 rack which is a faster steering upgrade - the non M rack. It is the same rack for all models from 96-02 except for M cars which got the slower rack.

    -Mark
    Quote Originally Posted by pbonsalb View Post
    So the Z3 non-M 6 cylinder rack is the same as the Z3 1.8 four rack?
    Is that not what I just said?

    Quote Originally Posted by golgo13 View Post
    Can someone just post up a part number? Would really simplify things.
    2 minutes later on RealOEM...

    https://www.realoem.com/bmw/enUS/par...&q=32131092611

    You can see it is the same part number for all non-M Z3:

    Part 32131092611 was found on the following Z3 vehicles:

    Z3 E36, Z3 1.8, Roadster, M43, EUR, (CJ11) : Power steering
    Z3 E36, Z3 1.9, Roadster, M44, EUR, (CH71) : Power steering
    Z3 E36, Z3 1.9, Roadster, M44, EUR, (CH72) : Power steering
    Z3 E36, Z3 1.9, Roadster, M44, USA, (CH73) : Power steering
    Z3 E36, Z3 1.9, Roadster, M43, EUR, (CM11) : Power steering
    Z3 E36, Z3 1.9, Roadster, M43, EUR, (CM12) : Power steering
    Z3 E36, Z3 2.0, Roadster, M52, EUR, (CL31) : Power steering
    Z3 E36, Z3 2.0, Roadster, M52, EUR, (CL32) : Power steering
    Z3 E36, Z3 2.2i, Roadster, M54, EUR, (CN11) : Power steering
    Z3 E36, Z3 2.2i, Roadster, M54, EUR, (CN12) : Power steering
    Z3 E36, Z3 2.5, Roadster, M52, USA, (CH93) : Power steering
    Z3 E36, Z3 2.5i, Roadster, M54, USA, (CN33) : Power steering
    Z3 E36, Z3 2.8, Coupe, M52, EUR, (CK31) : Power steering
    Z3 E36, Z3 2.8, Coupe, M52, EUR, (CK51) : Power steering
    Z3 E36, Z3 2.8, Coupe, M52, USA, (CK53) : Power steering
    Z3 E36, Z3 2.8, Roadster, M52, EUR, (CH31) : Power steering
    Z3 E36, Z3 2.8, Roadster, M52, EUR, (CH32) : Power steering
    Z3 E36, Z3 2.8, Roadster, M52, USA, (CH33) : Power steering
    Z3 E36, Z3 2.8, Roadster, M52, EUR, (CJ31) : Power steering
    Z3 E36, Z3 2.8, Roadster, M52, EUR, (CJ32) : Power steering
    Z3 E36, Z3 2.8, Roadster, M52, USA, (CJ33) : Power steering
    Z3 E36, Z3 3.0i, Coupe, M54, EUR, (CK71) : Power steering
    Z3 E36, Z3 3.0i, Coupe, M54, USA, (CK73) : Power steering
    Z3 E36, Z3 3.0i, Roadster, M54, EUR, (CN51) : Power steering
    Z3 E36, Z3 3.0i, Roadster, M54, EUR, (CN52) : Power steering
    Z3 E36, Z3 3.0i, Roadster, M54, USA, (CN53) : Power steering
    -Mark

  18. #18
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    Sorry to make you so impatient, Mark. I have actually been here longer than you and contributed much more than you, but my recollection was that the rack to buy was the Z3 1.8 rack, which is why I asked my question. If you can’t be polite, you should simply not answer and save your energy for replies to posts you have more patience for. That is what I try to do sometimes.

  19. #19
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    Alternatively, the yellow tag rack out of the ZHP 330 is an excellent upgrade; slightly faster than the z3 and non-variable.

  20. #20
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    Quote Originally Posted by BlackHawkRacing View Post
    Alternatively, the yellow tag rack out of the ZHP 330 is an excellent upgrade; slightly faster than the z3 and non-variable.
    Do you know actual numbers on the rack? If it’s a drop in, I just might swap to that from my Z3 rack, because your steering can never be too fast. Barring that, I’ll do what I need to to fit an E92 M3 rack, because it’s a bunch faster than the Z3 one.

  21. #21
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    Quote Originally Posted by jakermac View Post
    Do you know actual numbers on the rack? If it’s a drop in, I just might swap to that from my Z3 rack, because your steering can never be too fast. Barring that, I’ll do what I need to to fit an E92 M3 rack, because it’s a bunch faster than the Z3 one.
    7852974712; I will warn you though, I have seen NUMEROUS people advertise that part number when it fact it is not a real yellow tag. Tag color is the easiest way to confirm. Yes it is a direct drop in.

    More info on the rack is here:
    https://forum.e46fanatics.com/showthread.php?t=954523

    Another alternative is the purple tag. Part number 7852974678. Same ratio as the yellow tag but it has a different internals and "doesn't feel as good" as a yellow tag. I that put that last item in quotes I have never driven a car with a purple tag and can't comment. That said, one being better than the other is all relative and I am told the purple tag is still a massive improvement over the stock E36 rack. Rack Doctor provides some information on the Purple vs Yellow tag in the second quote box of the first post in the above link.

    Finally, here is another thread with some information:
    https://www.bimmerforums.com/forum/s...-Rack-Upgrades

    In general, the racks are pretty easy to find; they pop up for sale often. The only issue is there is massive variability in the quality of the racks for sale, but I guess that is like any used car part. Best place is buy any rack is Rack Doctor; you will pay a premium and lose out on the core refund but IMO worth it for peace of mind.

  22. #22
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    Quote Originally Posted by pbonsalb View Post
    Sorry to make you so impatient, Mark. I have actually been here longer than you and contributed much more than you, but my recollection was that the rack to buy was the Z3 1.8 rack, which is why I asked my question. If you can’t be polite, you should simply not answer and save your energy for replies to posts you have more patience for. That is what I try to do sometimes.
    I am not really sure if you can say you have contributed "much more than me"... if this thread is any example, I would suggest that my posts have been pretty helpful even if you didn't like my tone. I took the time to research an answer for you, format it to make it easier to read, and cite the source of my research so others in future can do it themselves.

    -Mark

  23. #23
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    Defensive and impatient. Read my 20,000 posts since 2005.

  24. #24
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    UPDATE.

    No, my wheel bearings are fine (and less than 1 year old). Everything is solid. The only thing I can think of is the MRT kit flexes enough to allow the LCA to push into the brake rotor. If car weights 3000 lb, and 1.4G's, then 1,000lbs force in the direction of the red arrow (into the page) in the 2nd picture. That's the only thing I can think of that's causing this. Also, this is a 95 M3, and different knuckles than others. So maybe that has something to do with it.

    Static clearance between the LCA and the rotor was roughly 4mm.

    Anyone with the SLR kit running a larger than stock diameter rotor? Had any problems.?

    IMG_20200610_173111.jpg

    0003553_mrt-roll-center-bump-steer-angle-kit-compatible-with-e30-e36m_870.jpeg

  25. #25
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    Check the clearance when the wheel is turned at various spots and I bet you will see less than 4mm between LCA and rotor. I run a custom roll center correction setup with thicker rotors and I know I had to clearance the control arm to make it work. i also remember looking at it static (in one spot) and thinking it would be fine, and later on figuring out it wasn't depending on wheel position. Have seen the same on many other setups running roll center correction. Some control arms also have more 'meat' in those locations than others. Grinder will take it down easily.

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