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Thread: E36 M3 Rear Sway Bar Options

  1. #1
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    E36 M3 Rear Sway Bar Options

    I need to use a smaller rear sway bar on my E36 M3 track car, something close to the stock 20 mm bar. The car is lowered and has very short drop links that are designed to mate to aftermarket sway bars with a bolt passing through the drop link and the bladed end of the sway bar. The pictures I've been able to find of the OEM rear bar show it passing directly through the OEM drop link (i.e., no bolt).

    Does anyone know of an aftermarket rear sway bar of small diameter that has bladed ends? Alternatively, does anyone offer a really short, adjustable drop link that will accept the OEM rear sway bar?

  2. #2
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    Quote Originally Posted by fbirch View Post
    I need to use a smaller rear sway bar on my E36 M3 track car, something close to the stock 20 mm bar. The car is lowered and has very short drop links that are designed to mate to aftermarket sway bars with a bolt passing through the drop link and the bladed end of the sway bar. The pictures I've been able to find of the OEM rear bar show it passing directly through the OEM drop link (i.e., no bolt).

    Does anyone know of an aftermarket rear sway bar of small diameter that has bladed ends? Alternatively, does anyone offer a really short, adjustable drop link that will accept the OEM rear sway bar?
    Look into GC rear small bar. It can be adjusted softer than stock or stiffer than stock.

  3. #3
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    Could also just run no rear sway bar (if your spring rates are high enough).

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    Quote Originally Posted by jayjaya29 View Post
    Could also just run no rear sway bar (if your spring rates are high enough).
    Thanks, it seems that lots of E36 race cars run with no rear bar. At my last event I started with the Turner sway bar combo that has a 30 mm front bar and 24 mm rear. Way too tail happy with this setup. Then I disconnected the rear bar and ran the last two sessions with no rear bar and the front bar set on soft. It definitely killed the oversteer, but I got tons of push in 3-4 key turns on my home track. The back end also felt very lazy.

    At my next event I'll try a 27 mm front bar that I already own and no rear bar. I also have an OEM 24 mm front bar that I can try with no rear. Since I already own all these bars it won't cost anything to try those combos. If I don't like any of the "no-rear-bar" combos then I'll try the small GC bar as suggested by r0nd3L.

    - - - Updated - - -

    Quote Originally Posted by r0nd3L View Post
    Look into GC rear small bar. It can be adjusted softer than stock or stiffer than stock.
    Thanks for the suggestion! I called GC and they tell me their small rear bar has torsional stiffness equivalent to a 16 mm to 22 mm solid bar, depending on which hole you use. If I don't like any of the no-rear-bar combos that I plan to try next, then I'll definitely try the GC rear.

  5. #5
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    You'd be surprised to hear that you probably want MORE front bar to help reduce understeer.

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    Quote Originally Posted by jakermac View Post
    You'd be surprised to hear that you probably want MORE front bar to help reduce understeer.
    What bar combo do you run, and is your car set up for road course racing/DE or autoX?

    The 30 mm front bar that is currently on my car is the biggest one I see advertised anywhere. I don't think I can go any bigger on the front. The problem is that with my 24 mm rear bar on full soft, the car is way too tail happy. With the rear bar disconnected altogether it pushes too much and is hard to rotate when I want it to do so.

    So is it your recommendation to leave the 30mm front bar and just find a smaller rear bar, such as the small GC rear?

  7. #7
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    I run my car (autox) with the GC 32mm hollow small (thinest wall) front bar (Its not enough bar, need bigger) 800lb front springs, 900lb rear springs and no rear bar. Alignment is 4 degrees negative camber in the front and 2.5-2.8 degrees in the back. It puts power down very nicely off the corners and responds very well in the transitions. It's the sweepers that don't work. Not enough front bite because of too much roll. You can clearly see it in the pictures. It's even bad enough that the inside rear gets off the ground from time to time. Adding a rear sway bar is not going to fix that.

  8. #8
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    Quote Originally Posted by jakermac View Post
    I run my car (autox) with the GC 32mm hollow small (thinest wall) front bar (Its not enough bar, need bigger) 800lb front springs, 900lb rear springs and no rear bar. Alignment is 4 degrees negative camber in the front and 2.5-2.8 degrees in the back. It puts power down very nicely off the corners and responds very well in the transitions. It's the sweepers that don't work. Not enough front bite because of too much roll. You can clearly see it in the pictures. It's even bad enough that the inside rear gets off the ground from time to time. Adding a rear sway bar is not going to fix that.
    Sounds as if your front bar is probably less torsionally rigid than the 27 mm solid Turner bar I just dropped down to on my car. I have some images of my car on track in high-g turns and the front and rear wheels appear to be very square to the ground. My tread temps also look to be relatively well balanced inside to outside, although the car picks up the inside front wheel in high-g turns.

    Although I haven't yet tried the 27 mm front (solid) / no rear bar combo yet, I ordered the Ground Control small rear bar. It was on sale Black Friday, so I went ahead and bought one. As stated above, The GC small rear is equivalent to a 16 mm - 22 mm solid rear, and the folks at GC told me they specifically developed this non-rigid rear bar for race cars, with good geometry for low ride height and not too much torsional stiffness. The fastest E36 at my local track runs a small rear bar with fresh tires and disconnects the rear bar as the tries wear. The GC small rear bar looks to have 5 different settings between 16 and 22 mm, so it should be good for fine tuning a given fore/aft balance.

  9. #9
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    Quote Originally Posted by fbirch View Post
    Sounds as if your front bar is probably less torsionally rigid than the 27 mm solid Turner bar I just dropped down to on my car.
    Yep! I've found that out the hard way. Someone did some fancy math for me and it seems like my front bar has an effective wheel rate of about 181lbs whereas the H&R 28mm bar has about 430lbs. That's one of the reasons why I say I need more front bar.

  10. #10
    NeilM is offline Member BMW E36 M3 Expert
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    Hotchkis 33.4mm hollow front bar here, with 24mm rear, springs 600F/700R, car is maybe 70 lb lighter than stock. Note that you need all this info to think usefully about the comparisons.

    For solid bars the first approximation for torsional stiffness is that it's proportional to the fourth power of the diameter (assuming the same construction, geometry and material). That 28mm H&R bar is about 220% of the stiffness of the stock 24mm front bar on my 96 M3. (For hollow bars you compute as if it were solid, then repeat the calculation for the imaginary bar that would fill the void and subtract that out.) This fourth power relationship also means that small bar diameter differences have significant effects. For instance a 24mm bar is more than 40% stiffer than a 22mm.

    I've noticed that swaybar vendors, when they give you any useful stiffness numbers at all, sometimes get sloppy on the terminology of when their product is 200% of stock or 200% stiffer than stock, which aren't the same thing.

    Neil

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    So what would be the equivalent solid bar diameter with the same stiffness as your 33 mm hollow front bar? Is your 24 mm rear also hollow or is it solid?

    My car has 685F/800R springs and I'm running about -3.4F/-2.2R camber. Currently I have a 27 mm solid front bar (just dropped down from 30 mm solid front) and the rear bar is disconnected. If the weather cooperates tomorrow I'll try that combo on track and report back here.

  12. #12
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    Just returned from the track. Only ran two sessions all weekend. For both, the 27 mm front solid bar was set to the middle position (3 hole bar) and the rear bar was disconnected. This gave a vast handling improvement over my previous setup - 30 mm front bar on soft and rear bar disconnected. Whereas the 30mm F/no rear combo gave me tons of push in slow, high-G corners, the smaller front bar greatly reduced push in those same corners. the 27 mm front bar still gave just a bit more push than I'd like, but it was a huge improvement from the bigger front bar. The front end also felt more composed over the bumpy parts of the track.

    With no rear bar the car really puts down the power on corner exit without the tail happiness I had before, but it's hard to get the tail to rotate when I want. NO matter how hard I tried to trail brake, the back end just didn't want to rotate.

    For my next outing I'm going to try moving the front 27 mm bar to full stiff and installing the small Ground Control rear on full soft (16 mm equivalent). I'm hoping to preserve the great rear end stability when powering out of the corner with no rear bar, while also allowing me to rotate the car just a bit under trail braking.

  13. #13
    NeilM is offline Member BMW E36 M3 Expert
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    Quote Originally Posted by fbirch View Post
    So what would be the equivalent solid bar diameter with the same stiffness as your 33 mm hollow front bar? Is your 24 mm rear also hollow or is it solid?.
    I did once measure the 33mm hollow bar's wall thickness and calculate its stiffness, but apparently didn't keep that spreadsheet. The car is currently in winter storage, so I can't repeat that right now.

    However the Hotchkis web site says its hollow front bar range is "300% and 380% stiffer than stock M3". That can't be correct as written, since a solid 33mm bar would be about 424% vs. stock, or 324% stiffer than stock. The next question would be stiffer than which M3? The 96+ has a 23mm stock front bar (let's call this 100%), but the 95 has a 22.5mm bar (92% of stock 96+). Since I don't know mine's wall thickness, let's pick a likely range and run the numbers. For a 3mm wall thickness the hollow bar's stiffness calculates to around 234% of the stock 96 M3, and at 4mm wall thickness 284% of stock. Your 27mm bar would be around 190% of stock.

    So assuming my assumptions are reasonable — err wait, compounding assumptions does sound a bit dodgy! — my 33mm hollow bar is likely to be a fair bit stiffer than your 27mm solid version. It may be a bit stiffer than your previous 30mm solid bar (but lighter in weight). That's about as close as I can get using the quick-and-dirty assumptions method.

    My 24mm rear bar is solid. Stock 96+ rear is 20mm, so mine is more than twice as stiff as stock.

    My car has 685F/800R springs and I'm running about -3.4F/-2.2R camber. Currently I have a 27 mm solid front bar (just dropped down from 30 mm solid front) and the rear bar is disconnected. If the weather cooperates tomorrow I'll try that combo on track and report back here.
    So not that different from my car — somewhat stiffer springs, about the same camber. However the outcomes will vary depending on car weight.

    Quote Originally Posted by fbirch View Post
    Just returned from the track. Only ran two sessions all weekend. For both, the 27 mm front solid bar was set to the middle position (3 hole bar) and the rear bar was disconnected. This gave a vast handling improvement over my previous setup - 30 mm front bar on soft and rear bar disconnected. Whereas the 30mm F/no rear combo gave me tons of push in slow, high-G corners, the smaller front bar greatly reduced push in those same corners. the 27 mm front bar still gave just a bit more push than I'd like, but it was a huge improvement from the bigger front bar. The front end also felt more composed over the bumpy parts of the track.

    With no rear bar the car really puts down the power on corner exit without the tail happiness I had before, but it's hard to get the tail to rotate when I want. NO matter how hard I tried to trail brake, the back end just didn't want to rotate.

    For my next outing I'm going to try moving the front 27 mm bar to full stiff and installing the small Ground Control rear on full soft (16 mm equivalent). I'm hoping to preserve the great rear end stability when powering out of the corner with no rear bar, while also allowing me to rotate the car just a bit under trail braking.
    Sounds reasonable. It'll be interesting to hear how that works out.

    My own thought process is this:
    - Pick the springs that give the driving experience you want/need. (For me that means driving possibly long distances to the track, but no daily driving)
    - As much front bar as needed to overcome the geometric deficiencies of the McPherson strut front suspension setup (esp. on lowered cars)
    - Rear bar as necessary to balance the car front/rear and allow rotation
    - Iterate until you're happy with the results.

    I can't over-emphasize the "driving experience you want" and "happy with the results" parts. What I like might suck for you, and vice versa. That said, in principle I think the no rear bar option is more applicable to cars that get their rear roll stiffness from relatively high rate springs. Dissenting opinions welcome!

    Neil
    Last edited by NeilM; 12-03-2018 at 03:01 PM.

  14. #14
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    Neil - Thanks for the excellent feedback. I agree 100% that a lot of it comes down to user preference, as well as track specifics, tire choice, driving style, etc.

    I have about a month and a half to play around with settings before the 2019 racing season starts up in late Jan, so I'll try to get in a few practice days and report back on what I learn. BTW, my car weighs a tick over 2800 lb with no driver and minimum fuel.

  15. #15
    NeilM is offline Member BMW E36 M3 Expert
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    One more thing to add: heavy front sways can lead to failure of the chassis mounts. Ask me how I know...and that was with a much smaller (25.4mm) bar. Here's the 2009 thread,
    https://www.bimmerforums.com/forum/s...=swaybar+mount

    Neil

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    Thanks for the heads up. I'll definitely keep an eye on them.

    Below are some pics of the GC rear sway. It appears to be well made. It's also very lightweight. The drop links have heim joints to avoid binding and are very nice looking. Good fitment overall. I'll report back when I've had a chance to try it out on track.

    GC rear sway_LR.jpg

    Drop link installed_LR.jpg

    Rear sway installed_LR.jpg

  17. #17
    NeilM is offline Member BMW E36 M3 Expert
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    Quote Originally Posted by fbirch View Post
    Below are some pics of the GC rear sway. It appears to be well made. It's also very lightweight.
    That's a really nice bar design. Hollow for light weight, and the flat plate side arms allow for a well thought out shape to minimize clearance issues where it passes between the LCA and halfshaft.

    Would you be able to post an as-installed pic like your last one above, except of the exhaust side? I have a clearance issue to the muffler canister there and would like to gauge how the GC bar might handle that.

    Neil

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    Below is a pic of the bar as it enters the muffler area on the driver’s side of the rear.

    The only tricky aspect of the installation was getting the bar to fit between the finned diff cover and the sheet metal that forms the spare tire well. The bar has an OD of 25 mm, so it was a bit tight getting it past the top of the diff cover. My car has the bulky finned diff cover from Rouge Engineering, so I probably have less clearance than a stock cover would offer. I inserted the end of a 1” X 6” board in that area and pried the spare tire sheet metal away from the diff cover very slightly. Not enough to be visibly changed, but it was just enough for the bar to slot right in. Of course I had to drop the muffler first. My car has a Supersprint muffler, which is both bulky and shockingly heavy.

    Diff & Muffler.jpg

    The two next pics show the arm of the bar as it crosses over the two pipes on the input side of the muffler. It looks tight in the pics but there’s actually a ton of clearance. One thing I’ll have to watch is that the ends of the bar extend about 0.5 in past the mounting bushing on each side. If I grab it with my hands I can move it left and right (I greased the bushings), so there is nothing that constrains left/right movement up to 0.5 in to either side. I’m hoping that equal force from the drop links will center it for the most part. It doesn’t hit anything when it moves left/right, but I don’t like the idea of it sliding around. Hopefully that won’t happen. I’ll check to see that it remains centered after the first session or two

    Muffler side 1.jpg

    Muffler side 2.jpg

    I put some calipers on it and the bar has a 25 mm OD and is about 2.5 mm thick. If you do the math, that corresponds to the same torsional rigidity as a 19 mm solid bar, which agrees perfectly with the info I got from Ground Control. This is the thin walled version of their E36 bar, and they told me it’s equivalent to a solid bar 16 mm to 22 mm, depending on which of the five holes you use. The middle of that range is 19 mm, in agreement with my measurements. So it looks as if the five settings roughly correspond to 16, 17.5, 19, 20.5 and 22 mm solid rear bars. This will hopefully give me the fine tuning that I need to balance rear grip on corner exit with the ability to rotate the car.
    Last edited by fbirch; 12-14-2018 at 04:20 PM.

  19. #19
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    Follow-up: I jacked up the driver's rear (muffler side) to the point where the left rear tire was 5 inches off the ground. This is the condition that swings the sway bar arm down toward the exhaust pipe as it enters the muffler can. There was at least 0.5 in of clearance between the bottom of the sway bar arm and the top of the exhaust pipe, so tons of clearance even at full droop.

  20. #20
    NeilM is offline Member BMW E36 M3 Expert
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    Quote Originally Posted by fbirch View Post
    Below is a pic of the bar as it enters the muffler area on the driver’s side of the rear.
    Thanks for the extra pix — very helpful.

    Oddly enough I have the SS muffler and Rogue diff cover too, and also found it beneficial to do a bit of clearancing with a BFH on the spare wheel well.

    One thing I’ll have to watch is that the ends of the bar extend about 0.5 in past the mounting bushing on each side. If I grab it with my hands I can move it left and right (I greased the bushings), so there is nothing that constrains left/right movement up to 0.5 in to either side. I’m hoping that equal force from the drop links will center it for the most part. It doesn’t hit anything when it moves left/right, but I don’t like the idea of it sliding around. Hopefully that won’t happen. I’ll check to see that it remains centered after the first session or two.
    The bar will laterally self-adjust over time, although not necessarily to the position you might wish! The APR rear bar I have for my Golf R has lateral stops welded on:



    I haven't seen BMW bars like that. It would be possible to use a pair of split collars to provide the same functionality.

    Quote Originally Posted by fbirch View Post
    Follow-up: I jacked up the driver's rear (muffler side) to the point where the left rear tire was 5 inches off the ground. This is the condition that swings the sway bar arm down toward the exhaust pipe as it enters the muffler can. There was at least 0.5 in of clearance between the bottom of the sway bar arm and the top of the exhaust pipe, so tons of clearance even at full droop.
    Briefly, to minimize the thread jack, there's an issue on my car where the length stack-up of the shorty headers + stock cat section + catback SS muffler is such that the muffler ends up maybe 15mm forward of where it should be. This results in the bar occasionally knocking on the exhaust when the suspension moves as you describe. It's difficult to modify the exhaust system, so I'm wondering about a differently configured sway bar. Hard to know if that'll help without trying it though.

    Neil

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    FBirch, thanks for taking the time to post the pics and share the info. I like the looks of the range of adjustability that GC bar has. I dislike swapping in a whole different bar to get a change in rear roll, pretty big PITA in the paddock.
    If God meant for man to motor-swap LS engines into track cars, He wouldn't have created Corvettes.

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