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      10-25-2012, 08:18 AM   #1
LiM3y
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Front only sway bars?

I have been musing about getting sway bars put on my car. The front one seems and easy job, but the rear is a PITA. I see that the Dinan suspension kit only has a front sway bar.

Is there any value in just adding a stiffer front sway bar, or will it just unbalance the suspension too much? (I don't know enough about suspension tuning to know the answer of just stiffening the front end). I was thinking of trying it up front for a cheap handling mod, before committing to 4 hours of labour to fit complimentary rear bar (and potentially another 4 hours to put the old one back!)
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      10-25-2012, 08:23 AM   #2
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Someone feel free to correct me if I'm wrong here, but I think stiffer front bars cause more understeer and stiffer rear bars cause less understeer (more oversteer). I wouldn't add a front bar only, because I don't want more understeer. Sways are a fine tuning device anyway, they don't make an ill-handling car handle properly or vice versa.
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      10-25-2012, 09:05 AM   #3
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Quote:
Originally Posted by Porschefile View Post
Someone feel free to correct me if I'm wrong here, but I think stiffer front bars cause more understeer and stiffer rear bars cause less understeer (more oversteer). I wouldn't add a front bar only, because I don't want more understeer. Sways are a fine tuning device anyway, they don't make an ill-handling car handle properly or vice versa.
I have no experience with sway bars on the e9x M3 but the e46 M3 really likes a stiffer front sway bar (relative to the rear) because it greatly improved/controlled the camber curve - stiffer bar actually reduced understeer (obviously there's an upper limit). I believe the e9x has a better camber curve and it this shows up in static camber settings - e46 requires a lot of front camber (more than neg 3-3.5 deg if using r-comps) whereas the e9x does not.

As for the Dinan front bar I think it is designed to work with their spring kit so not sure what effect - over or under steer - it would have on the handling characteristics of a stock e9x suspension?
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      10-25-2012, 09:14 AM   #4
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[I have Eibach Pro-kit springs]
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      10-25-2012, 11:46 AM   #5
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Quote:
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Someone feel free to correct me if I'm wrong here, but I think stiffer front bars cause more understeer and stiffer rear bars cause less understeer (more oversteer). I wouldn't add a front bar only, because I don't want more understeer. Sways are a fine tuning device anyway, they don't make an ill-handling car handle properly or vice versa.
Typically, in a neutral chassis with double wishbone suspension up front where suspension geometry upon compression is more "predictable," that would be the case.

However, the MacPherson strut design up front actually behaves unpredictably with addition of swaybars up front, especially if the swaybars manage to reduce the "reduced camber" effect when there's too much compression. I've seen cases where additional front stiffness actually ADDED front end grip and alleviated understeer on a BMW. However, that is in combination with a ton of negative camber up front already and a moderately stiff front suspension setup without the ability to independently adjust compression. On a stock-ish suspension, I suspect if you can get up to 2.5-3 of negative camber, adding swaybar up front only may actually IMPROVE the front end grip on an M3.

But not on a car with mostly stock front camber.
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      10-25-2012, 02:22 PM   #6
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Quote:
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Typically, in a neutral chassis with double wishbone suspension up front where suspension geometry upon compression is more "predictable," that would be the case.

However, the MacPherson strut design up front actually behaves unpredictably with addition of swaybars up front, especially if the swaybars manage to reduce the "reduced camber" effect when there's too much compression. I've seen cases where additional front stiffness actually ADDED front end grip and alleviated understeer on a BMW. However, that is in combination with a ton of negative camber up front already and a moderately stiff front suspension setup without the ability to independently adjust compression. On a stock-ish suspension, I suspect if you can get up to 2.5-3 of negative camber, adding swaybar up front only may actually IMPROVE the front end grip on an M3.

But not on a car with mostly stock front camber.
Interesting, so on my setup (514/800# and -2.5) a stiffer front bar should decrease understeer?
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      10-25-2012, 06:15 PM   #7
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Interesting, so on my setup (514/800# and -2.5) a stiffer front bar should decrease understeer?
COULD, not should. There's really no way to know for sure unless you test.
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      10-26-2012, 10:32 PM   #8
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I've got the dinan stage II with GC camber plates at -3.0 with square 275s. My E90 does not understeer at all unless I get totally retarded when turning in. In fact, its a little too much on the oversteer side. I'm going to try -2.5 at some point in the future and see if it makes the car more neutral.

Maybe I'm used to my 330 but it feels like I'm always working the keep the back end in the back.
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      10-28-2012, 10:27 AM   #9
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Quote:
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I've got the dinan stage II with GC camber plates at -3.0 with square 275s. My E90 does not understeer at all unless I get totally retarded when turning in. In fact, its a little too much on the oversteer side. I'm going to try -2.5 at some point in the future and see if it makes the car more neutral.

Maybe I'm used to my 330 but it feels like I'm always working the keep the back end in the back.
So did your car have the over-steering characteristics/feel before you installed the front-only sway bar?
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      10-28-2012, 11:11 AM   #10
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So did your car have the over-steering characteristics/feel before you installed the front-only sway bar?
Not sure if it was the sway bar, square tires, camber plates or a combination of all of the above.
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      10-29-2012, 10:35 AM   #11
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Quote:
Originally Posted by bigjae1976 View Post
I've got the dinan stage II with GC camber plates at -3.0 with square 275s. My E90 does not understeer at all unless I get totally retarded when turning in. In fact, its a little too much on the oversteer side. I'm going to try -2.5 at some point in the future and see if it makes the car more neutral.

Maybe I'm used to my 330 but it feels like I'm always working the keep the back end in the back.
I am in the same boat. Stock suspension w/GC plates -1.8 back, -2.8 front camber. Before the car would plow and I would hammer the gas at track out (slower speeds at steady state allowed for full throttle exits).

With increased grip, the rear is traction limited at track out. Thats the only place I see track out. Instead of reducing camber (front grip to compensate or negate to rear grip), my suggestion would be to run wider rubber at the back. I have a square setup now (275 Toyo R Comps) but will get a pair of 295 for the back.

We ran a staggered setup in the GT4 Vantage N24 and the car was much balanced.

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      10-29-2012, 11:12 AM   #12
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Quote:
Originally Posted by lutfy
Quote:
Originally Posted by bigjae1976 View Post
I've got the dinan stage II with GC camber plates at -3.0 with square 275s. My E90 does not understeer at all unless I get totally retarded when turning in. In fact, its a little too much on the oversteer side. I'm going to try -2.5 at some point in the future and see if it makes the car more neutral.

Maybe I'm used to my 330 but it feels like I'm always working the keep the back end in the back.
I am in the same boat. Stock suspension w/GC plates -1.8 back, -2.8 front camber. Before the car would plow and I would hammer the gas at track out (slower speeds at steady state allowed for full throttle exits).

With increased grip, the rear is traction limited at track out. Thats the only place I see track out. Instead of reducing camber (front grip to compensate or negate to rear grip), my suggestion would be to run wider rubber at the back. I have a square setup now (275 Toyo R Comps) but will get a pair of 295 for the back.

We ran a staggered setup in the GT4 Vantage N24 and the car was much balanced.

Lutfy
Thanks. I was planning on trying a staggered setup in the future. Yeah, it can be a handful at times but it goes through slower corners like a much lighter car.
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      10-29-2012, 02:05 PM   #13
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Start by adding a 5mm spacer to the rear. If you get wider rear tires, you will just induce push with the front. It will solve the throttle oversteer, but you will probably loose the crispness on turn-in. It sounds like the car is well balanced but just needs a tiny bit of rear grip. Try lowering your rear tire pressure 1-2 psi as well.

Some might say to be more patient on exit, but we all know that isn't fun at all
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      10-29-2012, 04:22 PM   #14
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Start by adding a 5mm spacer to the rear. If you get wider rear tires, you will just induce push with the front. It will solve the throttle oversteer, but you will probably loose the crispness on turn-in. It sounds like the car is well balanced but just needs a tiny bit of rear grip. Try lowering your rear tire pressure 1-2 psi as well.

Some might say to be more patient on exit, but we all know that isn't fun at all
Oversteer is way more fun than understeer! I don't track my M3 much so I haven't played with pressures yet. I just notice that I have to be a lot more mindful of what my rear end is doing in the M3 vs the 330. The 330 behaves much better.
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      10-29-2012, 04:50 PM   #15
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What are your toe settings at for the rear?
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      10-29-2012, 04:56 PM   #16
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When diagnosing handling issues, it's important to note the subtle nuances of where and when the car is understeering or oversteering. You wouldn't fix an oversteer on entry issue the same way you would fix an oversteer on exit issue. Try and keep notes of where the car is doing something you dont like, what your settings are at, tire pressures, and if you can - look on video and see what your steering angle is at. All this information helps diagnose a handling issue much easier.
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      10-29-2012, 05:06 PM   #17
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I used the dinan Stage III specs (front and rear) but with more front camber. I ran 39psi hot on street tires. It tends to oversteer on exit. I can throw away one session were my rears were 47psi...definitely could tell it the tire pressures were too high while I was driving it.

If I come off the track and all of the pressures are equal on all 4 corners then I can say the car does lean towards oversteer. Not a huge issue though, I just keep my foot in the throttle and DRIFT BABY! I am asian so that is totally normal.
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      10-29-2012, 05:12 PM   #18
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so is it worth adding the front only as long as you have lowering springs?
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      10-29-2012, 05:32 PM   #19
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Quote:
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so is it worth adding the front only as long as you have lowering springs?
From a general suspension set up standpoint, no - not unless you're getting oversteer on track.

As mentioned before, a front sway will usually cause the car to understeer more - something you dont want if the car is set up to push from the factory anyways.

However, as seen in the thread, some people are reporting that a front sway can cure an understeer issue. I've not experience this myself. Your results my vary. My general suspension setup knowledge leads me to say that a front bar would cure an understeer issue, but i've never tried to fix one with a front bar - always a rear bar or alignment setting.
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      10-29-2012, 05:32 PM   #20
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If you drive the car on the track and have understeer issues, I think it is a step in the right direction.
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      10-29-2012, 05:36 PM   #21
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From a general suspension set up standpoint, no - not unless you're getting oversteer on track.

As mentioned before, a front sway will usually cause the car to understeer more - something you dont want if the car is set up to push from the factory anyways.

However, as seen in the thread, some people are reporting that a front sway can cure an understeer issue. I've not experience this myself. Your results my vary. My general suspension setup knowledge leads me to say that a front bar would cure an understeer issue, but i've never tried to fix one with a front bar - always a rear bar or alignment setting.
Typically in an E46 (suspension design is not that different, right?), most run the biggest front bar possible and a smallish rear bar. Some even skip using a rear bar..all in the name to banish understeer. Sheesh, Turner sells a 40mm front bar. If the normal thinking were to hold true, wouldn't a 40mm bar render your steering wheel useless?

I think the main difference with the E9X is that you don't have to do nearly as much to get the car close to neutral.
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      10-29-2012, 05:44 PM   #22
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Quote:
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Typically in an E46 (suspension design is not that different, right?), most run the biggest front bar possible and a smallish rear bar. Some even skip using a rear bar..all in the name to banish understeer. Sheesh, Turner sells a 40mm front bar. If the normal thinking were to hold true, wouldn't a 40mm bar render your steering wheel useless?

I think the main difference with the E9X is that you don't have to do nearly as much to get the car close to neutral.
I ran a 32mm front sway and no rear sway on my s2000 without aero - it handled beautifully. I added the front way to neutralize the oversteer the s2000 has after going to a non-staggered set up, then it still was still a touch loose in the rear, so I removed the rear sway all together.

With the proper camber up front on and M3 that a track setup would have - the rear would oversteer more due to more grip than before (all other things equal).

Last edited by GTM_Challenge; 10-29-2012 at 06:09 PM.
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