Higher spring rates w/o rear bar or not?

[jakermac]

IMHO, the only advantage of using a rear bar in autocross would be to allow a softer rear spring which makes it easier to put down power in a straight line (Pro Solo, etc...).

[z3papa]

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.

You changed my mind. You're not so stupid afterall. JK with you Pete

[noodlexyz]

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?

Spring rates are dictaced by a bunch of things, vehicle weight, tires, shocks, aero, ect. Again, its all to achieve a good vehicle balance.

-Ryan

[Evice]

Spring rates are dictaced by a bunch of things, vehicle weight, tires, shocks, aero, ect. Again, its all to achieve a good vehicle balance.

-Ryan

Throw ride height which determines the roll couple into that mix

[10speed]

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.

Considering 2 setups:

(1) Front and Rear swaybars

(2) Front swaybar, rear swaybar removed, and rear spring rate increased to match front and rear balance

Does the setup without the rear swaybar have advantages over the other, or again is it "roll resistance doesn't care where it comes from?"

Can the suspension on setup (2) articulate and put power down better?

[nondescript]

Bumpy track with 'personality' may benefit from softer springs and roll resistance added by option 1. Just sayin'

Driving at the COTA track currently, maybe not so much.

[illinipo]

Considering 2 setups:

(1) Front and Rear swaybars

(2) Front swaybar, rear swaybar removed, and rear spring rate increased to match front and rear balance

Does the setup without the rear swaybar have advantages over the other, or again is it "roll resistance doesn't care where it comes from?"

Can the suspension on setup (2) articulate and put power down better?

Like I said,

there are many positives to not using bars like fully independent suspension, lower weight, more droop travel, etc.

(2) will articulate better. Most new Jeeps have an electronically disconnecting swaybar for this purpose.

However, if you use the stiffer shock settings required by stiffer springs, sure, you might have a little bit harder time "putting power down" with (2). The key is to drive smoothly and not shock the tires. The stiffer your spring and damper setup, the easier it will be to send a torque spike through the tires and cause slip.

Bumpy track with 'personality' may benefit from softer springs and roll resistance added by option 1. Just sayin'

Driving at the COTA track currently, maybe not so much.

Yes, certainly course and driver dependent. As mentioned, the choice of spring rate usually comes after you picked weight, track width, aero, tire stiffness, and tire grip. The easy way to pick rates is develop an understanding of how high of ride frequency you can get away with on various surface sticky-nesses and personalities. Sometimes you just cant get down to 1-1.5 degrees per G in roll while keeping a low enough ride frequency for the racing surface... then you need to run a bar.

[CGS12]

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.

First off I just want to say I'm not trying to be a jerk and tell you your wrong just because I want to.

You maybe right that the car doesn't care about where it gets its roll resistance but how it reacts when it rolls does matter. Sway-bars are springs for the corners and will not effect the handling of the car when the car is level dive/squat or bumps, unless the swaybar is prelaoded. Compensating with stiffer springs to make up for the swaybars in roll means a stiffer sprung car in all situations weather in the middle of a corner or straight and level hitting a bump, riding over curbing or breaking ect.

Swaybars also effect roll couple and are used to tune it. Using ride height to change roll couple could change your corner balance. How is this a benefit?

I have read one of Puhn's more basic suspension tuning books and remember him talking a lot about how swaybars were very usefull. I have never read Milliken but I find it hard to believe that they would come to the conclusion that swaybars can be tuned out with spring rates. swaybars are used in Nascar, dirt Mod, Grand AM, Le Mons, Formula Ford and even Formula 1 although they look nothing like what a every day swaybar looks like they do essentially the same job. I realize that you have done calculations and math to come to your conclusions but what I ask is if your conclusions and intuition(which is the devil)are correct then why would every racing series and car with the exception of some high level rally cars use swaybars? Why are some race cars equipped with driver adjustable swaybars from within the car if they are not a useful suspension tuning tool? doing the math to figure out your suspension is good but what works on paper often doesn't work in reality. this isn't because suspension tuning is some black art its just very involved and the average joe doesnt have any where near whats needed to come to accurate conclusions. There is a reason suspension engineers are well paid and there is a reason OEM manufactures and racing teams use swaybars and its because they have a purpose. Also in your calculation have you determined the spring rate of your tires and based your spring rates off of that. thats what a race engineer would do. Can us average enthusiast do this, not really.

By the way the Difference between low compression turbo's and high compression turbo's have a all to do with todays better technology, reducing emmisions, and getting a rid of turbo lag. It has nothing to do with inter-cooling.

Again I,m not being a jerk

Oh and my comment about your shocks had to do with what you wrote in your build thread which I did read! I'm not convinced that changing shock dampening is use full at all to change the way a car handles unless it rains. If the spring is correctly damped its damped. People using adjustable shock to change handle is a bleed over from stock autox when only stock springs are aloud and people fake spring rate with shock dampening and N2 pressure.

[Rex1585]

Yes but no on the fact that sway bars are better. There is no black and white. There is a lot, and I mean a LOT of gray area. THE biggest problem with sway bars is they attach each side to one another. (Sometimes a desired effect)

Another thing is not everyone uses sway bars in all Racing series. It all boils down to what works for each individual driver. One of the biggest issues with using the sway bar on the rear as that has already been mentioned was the problem of attaching the outside wheel to the inside wheel. This hampers the ability to allow the suspension the ability to more easily attenuate over rough/undulating surfaces.

I recall back in ~2002 that many of the ALMS broadcasts were talking about suspension setup a decent amount, and in that some of the engineers were commenting on the fact they were not using sway bars to allow for better suspension attenuation. Many of them said that they outright wouldn't use them in the rain, and would disconnect them entirely from the suspension.

Again, the end all be all is that EVERYTHING on the setup needs to be designed to work with everything. There is no end all be all. Tire A may work better with higher SR and no bar, while tire B may work better with lower SR with bar.

Both setups have been shown to be successful on track and on auto-x.


Just my 0.02

[propcar]

Sway bars aren't springs for the corners because sway bars effect both sides of the suspension adding to one side and taking away from the other.

I also think referencing race cars that have heavily modified suspension geometry and use very different sway bars than what our cars use is kind of an unfair comparison.

Like Rex said, there are compromises to both set ups and probably effective methods of implementing both.

[CGS12]

Sway bars aren't springs for the corners because sway bars effect both sides of the suspension adding to one side and taking away from the other.

I also think referencing race cars that have heavily modified suspension geometry and use very different sway bars than what our cars use is kind of an unfair comparison.

Like Rex said, there are compromises to both set ups and probably effective methods of implementing both.

Really? Imagine your driving your BMW through a parking lot and you drive over a speed bump. Both you front struts compress at the same time and the swaybar that is attached to those two struts moves with them at the same time. No torsional twisting of the bar is made in this situation the bar just rotates in its bushings. Now take a corner at a decent speed. One strut compresses in the corner and one extends. This causes the attached swaybar to twist creating torsional resistance to the chassis of the car rolling. A temporary addition of "spring rate" from the swaybar. This is how you can add stiffer swaybar a to a car with out changing the comfortable ride of a street car. This isn't the right way to tune a cars handling but its the first thing a lot of people change to improve the handling of a daily drive without making the car annoying to drive like stiffer spring rate could.

My referencing modified costome designed race cars was to make the point that of all chassis that would allow racing engineers to not included swaybars they still do. And my question is why do they retain them if the car would handle better without them. And why would you want to remove swaybars from a car that can't have it's suspension pick up points changed at will like a costome built race car could?

[gradon]

I have the TRM COs on my 95 m3 with the 27mm UUC up front and no bar in the rear. It did the job for winning the Tuner 2 class with NCCBMWCCA last year.

[propcar]

I guess what I was trying to say is that unlike the spring being independent the bar affects both sides and doesn't that take away some load from the inside wheel when in a turn?

If roll can be controlled wouldn't it be better to be independent? Particularly on the driven wheels?

[illinipo]

...lots of excellent points...

Sounds like we're on the same page here. I don't recall calling you a jerk I did get a little long winded but felt it was necessary to fully explain my reasoning since this is still a new idea on bf.c.

Bars are a great tuning tool. In the class I run, driver adjustable bar is not allowed. And since I don't drive well enough to need to tune the car at any one particular event, I don't need the convenience of an adjustable bar. So, I'll take the 20lbs instead. Race engineers use them because their driver is consistent enough that the quick adjustment of a bar will fill the need to change balance on the fly. Bonus points if the driver can adjust it real-time.

Yes, changing heights changes wedge, but if you do the legwork ahead of time in the shop, you can have several points where you know how much wedge to add after making a height adjustment on one end of the car.

You're right that math and reality aren't the same. I'm not currently running exactly what my spreadsheets told me to. They said to run 600/750 with the 21.5mm front bar. I tried it, it understeered, so I took off the front bar and put 800 in the rear and it's perfect. This error is mostly the result of fudging tire stiffness and CG/RC heights...

At the end of the day,

There is no end all be all.

There are literally millions of possible setups that are simply different means to an end. As a driver and engineer, I prefer to set up cars without bars if I can. IMO the weight loss is reason enough.

[badmonkey]

Sounds like we're on the same page here. I don't recall calling you a jerk I did get a little long winded but felt it was necessary to fully explain my reasoning since this is still a new idea on bf.c.

Not a new idea, this debate is years old...

[illinipo]

Not a new idea, this debate is years old...

No bars at all is what I'm referring to with the "new idea". I haven't seen it before 'round these parts. Just FSAE stuff and some random RRAX threads here and there hashing out the details.

[Damon in STL]

Hmm.....maybe the thing to try is no rear bar....no front bar and helper springs? On my old suspension setup/car configuration I would carry the front inside tire through slow corners approximately 6" off the ground.

Or, maybe it is a progressive rate spring! Damn....more to think about!

Damon in STL

[yokoseiki]

Honestly even though I don't run a rear bar I want to. Like I said before, the problem with the Z3 is the stock one sucks. Throw in a really low ride height (my car) and a lowered subframe (about 10MM from stock) and it doesn't work. It was easier for me to remove it and use different springs in the rear. I tune some of the balance by just changing the front bar.

After I removed the bar I actually could "put the power down" better because of better suspension articulation / less rear bind. In addition the car is better under braking. I still I feel like I can achieve both of these things after I reconfigure a proper working rear bar.

It's just nice to have a rear bar because changing the settings on that is about 2X's easier then changing springs. I guess the actual change of the spring is easy but you have to set ride height, corner weight, blah blah blah....

[S14]

why lower the subframe?

[nondescript]

why lower the subframe?

I assume it is to try to keep the roll center somewhat in check as you lower the car - as the two ends behave differently and can get pretty goofy as you push the limits. At least that happens with e36's which share much on the front of the zed tre.

[albrazzi]

Honestly even though I don't run a rear bar I want to. Like I said before, the problem with the Z3 is the stock one sucks. Throw in a really low ride height (my car) and a lowered subframe (about 10MM from stock) and it doesn't work. It was easier for me to remove it and use different springs in the rear. I tune some of the balance by just changing the front bar.

After I removed the bar I actually could "put the power down" better because of better suspension articulation / less rear bind. In addition the car is better under braking. I still I feel like I can achieve both of these things after I reconfigure a proper working rear bar.

It's just nice to have a rear bar because changing the settings on that is about 2X's easier then changing springs. I guess the actual change of the spring is easy but you have to set ride height, corner weight, blah blah blah....

Why does the bar not work lowered, I have my own theories but want to hear yours first.

why lower the subframe?

I think he means raise, as in farther up into the studs and raising the roll center on a lowered car. I know AKG sells a kit to do just that and includes an offset diff bushing. On the E30 rear you gain toe faster than Camber so its just a method of lowering and mitigating the adverse effects of doing so.

[kenndoggy]

This old thread needs to be posted here, and read in it's entirety by everybody posting here:

http://forums.bimmerforums.com/forum...d.php?t=248893

[yokoseiki]

I guess relative to the ground it's "rasied" but lower means relative to the body. I actually just machined my Turner subframe bushings 10MM "lower" to move the subframe closer to the body.

Hope that clears it up. My car isn't a baja racer or anything like that.

In order to keep the rear bar from hitting the bottom of the car the arms connected to the trailing arms have to be super short. Since they are so short, it causes binding through part of the range of motion. It just made the car hard to drive.

[z3papa]

This old thread needs to be posted here, and read in it's entirety by everybody posting here:

http://forums.bimmerforums.com/forum...d.php?t=248893

Kenn -- read through that thread. Very informative but also so technical it could leave your head spinning a bit. Obviously, the three main players had some areas where they agreed, and others where they did not.

[illinipo]

Basically mostly right throughout, but getting bogged down in the difference between TLLT and TLLTD for most of the thread. With a bar, the total load transfer around the entire car is not changed, but the distribution is. Thinking that the total is changed is a common mistake for people new to the idea that swaybars transfer load (I made this mistake myself before seeing the total transfer light). I can go back and find the page in Milliken that explains this if people really want... But you can just do conservation of momentum on the moments on the chassis to prove it.

Oh, and the reason this is important is... if bars increased the total load transferred, then answering the question of springs vs. bars would be like eighth grade math.