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Thread: Higher spring rates w/o rear bar or not?

  1. #1
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    Higher spring rates w/o rear bar or not?

    Trying to decide which way to go with spring rates. 95 M3 trailered DE/track only car that should weigh less than 2800 lbs. Stiffer bushings and reinforcements are all done. Running Conti Grand Am or BFG R1 tires. Adjustable sways are a large tubular front bar and Eibach non-M 21mm in back. AST 4100 with Vorshlag plates. I had run 550#F / 700#R when the car had a full interior, but the rear springs are 6” and now that it’s lighter I can’t go low enough on them. So considering 2 options:

    #1 - keep the 550# front springs and get 650# rears (Vorshlag GTS recommendation). I would plan to keep the rear sway bar with this.
    #2 – 600# fronts with 784# rears (H&R 140-60-140 that I already have). This would be close to the Vorshlag GTR setup. Thinking I would probably ditch the rear sway bar.

    So what are the advantages/disadvantages of more spring rate with less/no rear bar and vice versa?
    Last edited by JPJ; 02-03-2013 at 12:02 PM.

  2. #2
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    Subscribed. Our 95 M3 is setup with GC coilovers - 650/850 and no rear bar. We're also running the GC race front sway. The car is not quite 100% ready for the track but I'll report back to this thread with our findings.

  3. #3
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    Quote Originally Posted by JSA View Post
    Subscribed. Our 95 M3 is setup with GC coilovers - 650/850 and no rear bar. We're also running the GC race front sway. The car is not quite 100% ready for the track but I'll report back to this thread with our findings.
    Are you running the medium or large GC bar? Can you give an accurate weight for the complete setup?
    Last edited by jakermac; 02-03-2013 at 12:11 PM.

  4. #4
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    At 2800lbs you should even be able to lose both bars. With race tires I would try something like 600/850 or 650/850 and play with front ride height (thereby playing with front roll center height) to get the balance right. From my notes,

    25mm front bar with bushings 12.4lb
    21.5mm front bar with bushings 9.8lb
    19mm rear bar with bushings, mounts, and brackets 7.4lb

    So you stand to lose around 20lbs getting rid of bars, plus the suspension then goes fully independent which is nice for the driver.

  5. #5
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    This is the first I have heard to lose the front also, but I'm in it to learn.
    I am running 500/650 RD sways full stiff front and just put the stock bar back on only street driving so far with this setup the Track will tell. I don't think with my springs I can remove the rear yet.

  6. #6
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    We are running sticky street tires (rs3) on a 2900lb z4 with no bars and 600/800, so the combination of -100lbs, 1-2 inch higher CG, and an extra .2-.3G from the tires could mean you'll still need a front bar even with 600 or 650 and 850. But for an easy 13lbs, I would try it

  7. #7
    noodlexyz's Avatar
    noodlexyz is offline Ryan - Mueller Motorwerks Supporting Vendor
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    Alright, here we go...

    My car set up last year yielded a pretty neutral car with a slight tendency to understeer in longer radius corners at the exit.

    Bilstein Group N's, 700#f 800#r springs, 27mm front bar on full stiff, no rear bar. Car estimated weight is 2800 lbs with 225/45/17 Conti slicks.

    Im going to use a non-m rear sway bar this season and see if I can get the car to oversteer a bit more on corner exit. I will also probably make a 50 to 100# spring jump after I see what the non-m rear bar does.

    Hope that helps!

    -Ryan
    1993 325is racing car type thing....

  8. #8
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    Quote Originally Posted by jakermac View Post
    Are you running the medium or large GC bar? Can you give an accurate weight for the complete setup?
    It's the largest sway bar. ~ 2,600 lbs.

  9. #9
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    Quote Originally Posted by JSA View Post
    It's the largest sway bar. ~ 2,600 lbs.
    Thanks. I was after the weight of the swaybar itself (bar and mounts, etc...).

  10. #10
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    I'd call around to some of the shops that actually race to get some advice on car set-up. To my knowledge there aren't many - if any - that advise to eliminate the rear bar regardless of the damper/spring combo.

    My old set-up was:
    GC front and rear bar (biggest bars available)
    AST 4200's
    fr 700
    rr 800

    Car was capable of 1:11's at NJMP Lightning and low 1:20.xx's at Summit Main with that set-up.

    Just some food for thought

    Will
    Last edited by will v; 02-03-2013 at 06:04 PM.

  11. #11
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    Running no rear bar is more commonly seen on an autocross course.

    I personally haven't seen anyone running track events without a rear bar. I'm sure it's possible, just not very common.
    Shawn
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  12. #12
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    It's not uncommon to not run a rear bar. Never heard of a BMW run without a front bar except when its wet.

    I don't run a rear bar on my car. You need significant spring rates to get rid of the rear bar. I run a stock (I.e. small) front bar. E30 M3 but the E36 doesn't differ that much in principle.
    It's not speed that kills, it's the speed difference that does. Obviously you aren't going fast enough.

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  13. #13
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    Quote Originally Posted by noodlexyz View Post
    Alright, here we go...

    My car set up last year yielded a pretty neutral car with a slight tendency to understeer in longer radius corners at the exit.

    Bilstein Group N's, 700#f 800#r springs, 27mm front bar on full stiff, no rear bar. Car estimated weight is 2800 lbs with 225/45/17 Conti slicks.

    Im going to use a non-m rear sway bar this season and see if I can get the car to oversteer a bit more on corner exit. I will also probably make a 50 to 100# spring jump after I see what the non-m rear bar does.

    Hope that helps!

    -Ryan
    Last I ran 650/750 on JRZ RS w/GC front sway no rear bar. Car was 3260 with me in it. Full AKG 75D bushings.

    The GC bar at medium induced corner entry understeer and was just slightly biased towards understeer everywhere else. I went to full soft and the car was perfect. There were also some slght damping adjustments.

    I would be motivated to just adjust the front bar softer, probably increasing grip in the front before limiting grip on the rear to balance the car.

    This year I'll be much lighter and may change my springs. First event is next weekend so we'll see.

    Quote Originally Posted by fourwhls View Post
    Running no rear bar is more commonly seen on an autocross course.

    I personally haven't seen anyone running track events without a rear bar. I'm sure it's possible, just not very common.
    It's common in NORCAL
    Last edited by jbass524; 02-03-2013 at 07:18 PM. Reason: Automerged Doublepost

  14. #14
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    Quote Originally Posted by JPJ View Post
    Trying to decide which way to go with spring rates. 95 M3 trailered DE/track only car that should weigh less than 2800 lbs. Stiffer bushings and reinforcements are all done. Running Conti Grand Am or BFG R1 tires. Adjustable sways are a large tubular front bar and Eibach non-M 21mm in back. AST 4100 with Vorshlag plates. I had run 550#F / 700#R when the car had a full interior, but the rear springs are 6” and now that it’s lighter I can’t go low enough on them. So considering 2 options:

    #1 - keep the 550# front springs and get 650# rears (Vorshlag GTS recommendation). I would plan to keep the rear sway bar with this.
    #2 – 600# fronts with 784# rears (H&R 140-60-140 that I already have). This would be close to the Vorshlag GTR setup. Thinking I would probably ditch the rear sway bar.

    So what are the advantages/disadvantages of more spring rate with less/no rear bar and vice versa?
    Does the car have any aero?

    IMO, I'd put the 700's up front and put 800's in the rear with the bar on full soft. Probably move the front bar to around 1" from the stops.

    The no rear sway works for some people, not for others. It never worked for me, the car felt lazy and had roll couple issues. It might work for auto-x, but on the race track with longer steady state corners, an adjustable rear bar really helps fine tune the chassis. I can't imagine removing the rear bar on a track/race E36, it is another adjustment that allows you to fine tune the balance of the car.
    Sean

  15. #15
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    My racecar is an IS at 2856 lbs with 1/4 tank fuel. I am running #500F, #600R with Eibach swaybars Fand R set at soft, TCK D/As. Recently got the track record at MidOhio. #550-600F, #700-750R is probably the most I'll ever go in terms of high spring rates depending on track.
    Last edited by Evice; 02-04-2013 at 07:40 AM.
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  16. #16
    NeilM is offline Member BMW E36 M3 Expert
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    Quote Originally Posted by Evice View Post
    My racecar is an IS at 2856 lbs with 1/4 tank fuel. I am running #500F, #600R with Eibach swaybars Fand R set at soft, TCK D/As. Recently got the track record at MidOhio.
    Unusually soft setup for a race car. I say that not at all to criticize—your results speak for themselves!—but to point out that driver preferences vary, and it's more important to come up with the setup that works for you than to adopt what someone else likes.

    Neil

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    Quote Originally Posted by NeilM View Post
    Unusually soft setup for a race car. I say that not at all to criticize—your results speak for themselves!—but to point out that driver preferences vary, and it's more important to come up with the setup that works for you than to adopt what someone else likes.

    Neil
    Well put! I share my car with my brother and we compromise on the set-up a bit. I like a lose car, he likes it to tend to understeer so we set it up as close to the middle as possible. It's all about the feel for most of us and what we like.

    -Ryan
    1993 325is racing car type thing....

  18. #18
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    Depends on the car. On a Z3 a lot of guys lose the rear bar to gain some suspension articulation. The stock bar position is terrible and the arms on the bar are very short.

    I don't run a rear bar but you have to have the correct spring rates to make it work. My spring rates are around 950# front and 580# rear with a coil over so that's like 1100-1200 ish. Car balance is still a slight understeer.
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  19. #19
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    Quote Originally Posted by Evice View Post
    My racecar is an IS at 2856 lbs with 1/4 tank fuel. I am running #500F, #600R with Eibach swaybars Fand R set at soft, TCK D/As. Recently got the track record at MidOhio. #550-600F, #700-750R is probably the most I'll ever go in terms of high spring rates depending on track.
    Why so soft...Because that's what TC said? Before saying its the most you'll ever go, why not go test with higher rates or stiffen the front bar. You might find the car goes even faster.
    Sean

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    Quote Originally Posted by NeilM View Post
    Unusually soft setup for a race car. I say that not at all to criticize—your results speak for themselves!—but to point out that driver preferences vary, and it's more important to come up with the setup that works for you than to adopt what someone else likes.

    Neil
    Driver and track dependent.

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  21. #21
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    Quote Originally Posted by SG_M3 View Post
    Does the car have any aero?

    IMO, I'd put the 700's up front and put 800's in the rear with the bar on full soft. Probably move the front bar to around 1" from the stops.

    The no rear sway works for some people, not for others. It never worked for me, the car felt lazy and had roll couple issues. It might work for auto-x, but on the race track with longer steady state corners, an adjustable rear bar really helps fine tune the chassis. I can't imagine removing the rear bar on a track/race E36, it is another adjustment that allows you to fine tune the balance of the car.
    I've run a myriad of rates (450-600F and 600-800R) with and without rear bar on a car weighing in at 2720# with AST 4200's. When I ran without a rear bar in part to get power to the ground in mid-exit corner when I still had a torsen LSD. Worked great at getting power but made the car lazy in fast transitions which happen more in autocross than tracking. It wasn't until the 2011 Nat'ls when I was watching my co-driver go through the slalom heavy West course I knew I needed a rear bar at least for that type of course.

    For tracks, I'm pretty confident I could go without a bar and the car would be great but am not so certain it would be for all types of courses in autocross.
    Now in E92 M3 ZCP -- Absolute beast

  22. #22
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    Quote Originally Posted by SG_M3 View Post

    Does the car have any aero?.
    No aero yet, maybe next year or the year after.

    I've decided to go with 600# front with the 784# rears. Maybe would have preferred 650's but another member had the 600's for sale, plus it's what Vorshlag recommends. Also my front bar isn't GC, it's a bar I bought used from VAC that I think Eibach custom made for one of their race cars. About 34mm hollow with 4 adjustment holes per side, so not really that heavy and lots of adjustment to play with. I can go stiffer there as needed rather than just with the springs. I'm going to keep the current rear bar full soft to start and see how it feels. I also have the original 95 M3 (19mm) and another really small non-M bar that I could play with vs. going no bar at all.

    Thanks for all the input, there's been some great discussion. Feel free to keep it going.

  23. #23
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    Quote Originally Posted by illinipo View Post
    At 2800lbs you should even be able to lose both bars. With race tires I would try something like 600/850 or 650/850 and play with front ride height (thereby playing with front roll center height) to get the balance right. From my notes,

    25mm front bar with bushings 12.4lb
    21.5mm front bar with bushings 9.8lb
    19mm rear bar with bushings, mounts, and brackets 7.4lb

    So you stand to lose around 20lbs getting rid of bars, plus the suspension then goes fully independent which is nice for the driver.
    What works for an autox car and a track car are really different. From alignment settings to spring rates little really crosses over and works for both.
    The OP has a DE car and a different car than yours. Recommending removing both sway bars on a track car when you yourself haven't proven that it works on your autox Z4 is giving so broad far reaching advise.
    Anti roll bars are a tuning tool and one you have removed from your suspension. I know your autoxing your car but I can't help but think your trying to tune your car with your shocks which is not going to help you when your mid corner.

  24. #24
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    Quote Originally Posted by SG_M3 View Post
    Why so soft...Because that's what TC said? Before saying its the most you'll ever go, why not go test with higher rates or stiffen the front bar. You might find the car goes even faster.
    If you ask TC he'll probably say go 400F, 500R ... I guess it doesn't hurt to try high rates may be like 800F, 900R or something but my shocks most probably can't work that. For couple tracks I am thinking of trying 600-650F/750R. May be after competition catches

    Let me ask you; Why high spring rates?
    Last edited by Evice; 02-04-2013 at 08:57 PM.
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  25. #25
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    Quote Originally Posted by CGS12 View Post
    What works for an autox car and a track car are really different. From alignment settings to spring rates little really crosses over and works for both.
    The OP has a DE car and a different car than yours. Recommending removing both sway bars on a track car when you yourself haven't proven that it works on your autox Z4 is giving so broad far reaching advise.
    Anti roll bars are a tuning tool and one you have removed from your suspension. I know your autoxing your car but I can't help but think your trying to tune your car with your shocks which is not going to help you when your mid corner.
    Allow me to draw a corollary. This is EXACTLY like the argument about using low compression for turbo engines. The only reason to use low compression is you have more of a chance to cool the compressed air before it gets to the cylinder using intercoolers. At the end of the day, cylinder pressure doesn't care where it comes from, be it boost or static compression. At the same final cylinder pressure, high boost/low compression and low boost/high compression will make about the same power, provided the same air charge temperature.

    By the same token, roll resistance doesn't care where it comes from (springs or bars). A car will act approximately the same (under or oversteer balance) whether the roll resistance comes from springs or bars. The only significant reason to use a bar is if you like to use the holes in the bar to tune balance, instead of using ride heights to adjust roll centers. On the other hand, there are many positives to not using bars like fully independent suspension, lower weight, more droop travel, etc. Based on my research, experience (admittedly somewhat limited), and intuition, if you can get all the roll resistance you need from springs, do it. This is also the way things are taught in several of the most respected suspension setup books (Milliken, Puhn, etc...), though they don't come right out and say it like I have.

    My suggestion is not based on a whim or a guess, and I have the spreadsheets to prove it. I haven't done the legwork for this particular 2800lb e36... my time isn't free. That's why I chose words like, "I would try..." and, "...could mean..." since the numbers I gave here were based on intuition from spending hours with my calipers, tape measure, and spreadsheets for the Z. By the way, my shocks are around 75-80% critical damping, and I don't use them to tune steady state balance (mid-corner, as you say) because they have nothing to do with steady state balance (aside from N2 pressure which few people have the tools to adjust).

    Regarding differences from track to autox, and the use of a rear bar, I don't fully buy any of it yet. There are several people who say they need in autox what others say they only use for track (including z3papa in this very thread!). Additionally, literally ALL of the car setup threads and posts I see here comparing bars and springs do absolutely nothing to maintain TLLTD (front to rear roll resistance bias) when adding/removing the rear bar. None of it is scientifically testing one single variable. So I'm not convinced of anything on that front. Based on my best information, with no personal experience setting up a track car, the fact that roll resistance doesn't care where it comes from still holds up in my mind over internet lore. I love to learn and hate to be wrong, so if someone has a proper test to show me proving otherwise, please do so.

    The OP is free to make his choice. This is the internet, I'm free to blab all I want and I am trying to help this community with new ideas, but you all don't have to listen to me. Enjoy your 20lb bars with holes to adjust balance and I will enjoy my fully independent suspension and raise/lower roll centers to adjust balance Just different means to an end.
    Last edited by illinipo; 02-05-2013 at 02:53 PM.

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