Under steer

[ianc]

People are doing the front bar only because it's cheap.

No, people are doing the front bar because without an LSD, they are getting too much wheelspin on corner exit to put the power down effectively.

Read post 17 in this thread for one example,

ianc

[bradford]

Originally Posted by ianc

No, people are doing the front bar because without an LSD, they are getting too much wheelspin on corner exit to put the power down effectively.

Read post 17 in this thread for one example,

ianc

Post 17 in this thread contains a link to an install where the poster installed M3 ARBs, front AND rear, and was satisfied with the results.

http://www.1addicts.com/forums/showp...9&postcount=17

[ianc]

My bad: 16

ianc

[timhatimay]

I have read on the forums in several places that people started to lift the rear wheel upon installing the rear M3 ARB (and thus losing traction w/o the LSD). I believe I've even read Harold and other suspension tuners say this before. I've heard quite a few people recommend it only be done with an LSD for this issue, and some of the others mentioned above. Also, I read from someone (maybe on e90?) that it started to make the car rotate almost too much (I believe the term snap-oversteer was used). Fine if it is a total auto-x car, but for more high speed tracks or street driving I wouldn't want this...maybe because I'm still inexperienced. Probably one of the experienced suspension tuners on the forums can give the best advise for this mod.

I guess moral of the story is that if you do decide to do this without an LSD, probably a smaller bar is the way to go. Also, as bradford mentioned, if you are in there do the subframe bushings! You could always start with the front (because its cheap and easy), then do the rear if you want more.

Tim

[bradford]

Originally Posted by ianc

My bad: 16

ianc

The poster in #16 used an H&R bar. I'm not sure where that bar stands on the stiffness scale in relation to the OEM M3 bar, but I suspect it might be stiffer. Bear in mind that I already said stiffer is not necessarily better. It's a balance thing.

[bradford]

Originally Posted by timhatimay

I have read on the forums in several places that people started to lift the rear wheel upon installing the rear M3 ARB (and thus losing traction w/o the LSD). I believe I've even read Harold and other suspension tuners say this before. I've heard quite a few people recommend it only be done with an LSD for this issue, and some of the others mentioned above. Also, I read from someone (maybe on e90?) that it started to make the car rotate almost too much (I believe the term snap-oversteer was used). Fine if it is a total auto-x car, but for more high speed tracks or street driving I wouldn't want this...maybe because I'm still inexperienced. Probably one of the experienced suspension tuners on the forums can give the best advise for this mod.

I've got M3 bars, front and rear, and I don't have excessive traction loss at corner exit. That being said, I've got M3 links, camber plates, and coilovers...

[GaryS]

Originally Posted by bradford

I've got M3 bars, front and rear, and I don't have excessive traction loss at corner exit. That being said, I've got M3 links, camber plates, and coilovers...

Okay, I'll restate the consensus as, If you add a stiffer rear bar without LSD, you better know what you're doing, or you might end up with excessive wheel spin.

[gumpy]

Has anyone tried just an upgraded aftermarket strut tower brace to see if it reduces understeer by reducing strut tower deflection?

Gumpy.

[GaryS]

In case anyone is interested, I just spoke with a Dinan SA about a Dinan rear swaybar for my car. For reference, I have BMW Performance springs, FSD shocks and M3 front arms and bar (26.5mm); and the Dinan rear bar is 15.8mm vs the 20mm M3 rear bar. The Dinan SA said Dinan does not recommend changing the rear bar on 135i's because the stock bar is already the right size to match the 26.5mm M3 front bar. So I tried, but Dinan doesn't want my money. So it's going to be subframe bushings only.

[HP Autosport]

Originally Posted by GaryS

Okay, I'll restate the consensus as, If you add a stiffer rear bar without LSD, you better know what you're doing, or you might end up with excessive wheel spin.

One can certainly adjust his/her driving style to limit wheel spin.

[vitig]

My conclusion is that the m3 front bar of 26,5 cm is good whit the stock rear bar(12mm) and if you mount the m3 28mm must be mount the 335M bar 15mm.

Is possible that change my rear bar of 20mm for the 15mm and mount performance springs to upload the height.

I read more about dinan(good i+d) and good advice from harold of hp.

[GaryS]

Originally Posted by vitig

My conclusion is that the m3 front bar of 26,5 cm is good whit the stock rear bar(12mm) and if you mount the m3 28mm must be mount the 335M bar 15mm.

Is possible that change my rear bar of 20mm for the 15mm and mount performance springs to upload the height.

I read more about dinan(good i+d) and good advice from harold of hp.

I am sticking with the 26.5 mm M3 front bar and the stock rear bar for now because my car feels balanced. Wavetrac is on order. I will sort out wheels and possibly Dinan camber plates next and then see if a stiffer rear bar makes sense.

[fboutlaw]

So I think what hasn't been mentioned in this thread is balance.

What you are doing by changing the sway bar is limiting your car's ability to roll about the car's roll center. As there are 2 sway bars, you have to keep them in balance, but the problem with the 1 is that BMW has it a bit off to get the car slightly understeering which is how all cars are delivered to customers. What people in the forum are doing is changing the front sway bar to the size that BMW puts in the 135i convertible (1" thick). This is actually a more balanced setup and the front and the rear sway bars are more in sync with this setup.

The problem with too stiff of a rear sway without a LSD is that the sway tries to get your tires to maintain the same distance to your wheel well. When you compress the outer in a turn, the sway bar tries to get the inside tire to lift up. Without a LSD, the tire with the least amount of grip is applying force, so what you've done is lessen your ability to apply force during cornering.

Keep the front and rear in balance, and you're good.

Dinan front sway bar here (along with full s3 suspension). Couldn't be happier.

[The1]

glad i read this thread, I've been trying to figure this out. I have an LSD on the way, already have M3 front installed, will be lowering and doing some other M3 parts...

I'm starting to think the dinan rear might be a good idea... 3mm is considerable, i know it sounds small, but with the setup i'm going for it might be a good idea.

[Remonster]

Originally Posted by HP Autowerks

One can certainly adjust his/her driving style to limit wheel spin.

but...then you're slower, you get more wheel spin because there's less grip at the rear coming out of a corner.

[sodara]

Hmmm, nice to see an old post still active. After 6 autocross events with the e93 front sway bar, I removed it and went back to the stock bar. Yes, it does what it does(reduces body roll) and that is my perception - however, I didn't go to school on designing suspension. I hate to admit it, but with the M3 bar I had more under-steer. I was much faster with the stock bar. I'm glad to see posts of other driver's success but it's not working out for me (idk, maybe it's just me). I compete in D-stock dominated by Integra Type Rs and Minis...and my times were substantially slower with the M3 bar. This as been my experience and as a friend used to tell me, take everything with a grain of salt.

[The1]

Originally Posted by sodara

Hmmm, nice to see an old post still active. After 6 autocross events with the e93 front sway bar, I removed it and went back to the stock bar. Yes, it does what it does(reduces body roll) and that is my perception - however, I didn't go to school on designing suspension. I hate to admit it, but with the M3 bar I had more under-steer. I was much faster with the stock bar. I'm glad to see posts of other driver's success but it's not working out for me (idk, maybe it's just me). I compete in D-stock dominated by Integra Type Rs and Minis...and my times were substantially slower with the M3 bar. This as been my experience and as a friend used to tell me, take everything with a grain of salt.

my initial concerns with the M3 bar up front were like you said, a little understeer. however when i hit a banked onramp or a slightly banked corner somewhere, i find it's a lot faster.

i think as far as auto-xing goes, it's probably a useless upgrade as you're on flat level ground.

[stevend218]

I’ve got KW's V2's, and installed the UCC front sway bar, on the stiffest setting. im not 100% certain, but since the install of the sway i feel that my under steer has increased... as i said, im not 100% sure, just my initial thoughts.

[Lubo]

Originally Posted by sodara

Hmmm, nice to see an old post still active. After 6 autocross events with the e93 front sway bar, I removed it and went back to the stock bar. Yes, it does what it does(reduces body roll) and that is my perception - however, I didn't go to school on designing suspension. I hate to admit it, but with the M3 bar I had more under-steer. I was much faster with the stock bar. I'm glad to see posts of other driver's success but it's not working out for me (idk, maybe it's just me). I compete in D-stock dominated by Integra Type Rs and Minis...and my times were substantially slower with the M3 bar. This as been my experience and as a friend used to tell me, take everything with a grain of salt.

I always found softer suspension to be better at most auto-x. Most corners are sharp and low speed. with stiff suspension or too much sway it is very easy to overwhelm the tiny tires our 1ers have up front.

With stiffer front sway and spring/shock, you better have some wider and stickier tires

[vwrefugee]

These front sway discussions are really frustrating. The majority of reports here say that the sway helps with the understeer and it's a highly recommended upgrade. On the other hand, suspension tuning 101 says the way to address understeer with swaybars is to increase the rear bar, not the front. Still, there have been some reasonable explanations as to why increasing the front seems to work on these cars. But here we are with some experiences that support the conventional notion.

[Nick135i]

Originally Posted by vwrefugee

These front sway discussions are really frustrating. The majority of reports here say that the sway helps with the understeer and it's a highly recommended upgrade. On the other hand, suspension tuning 101 says the way to address understeer with swaybars is to increase the rear bar, not the front. Still, there have been some reasonable explanations as to why increasing the front seems to work on these cars. But here we are with some experiences that support the conventional notion.

vwrefugee,

I am not supprised that people get confused about this issue.

The primary reasons cars don't handle well (understeer in this case) is for two reasons (there are actually more - but to keep it simple - we will keep to the two primary reasons here)

1) Balance (The car is unbalanced - front to rear roll stiffness/springs/shocks/sway etc..)
2) geometry (bad camber angles etc...)

IMHO (I have some circuit racing experience) the 135i is a reasonably well balanced car with poor geometry. This means that the fundamentals of springs and sway bars are not too far away from ideal from a balance perspective. Perhaps they should be stiffened up a touch overall but the ratio's BMW choose are not fundamentally wrong.

On the other hand, the geometry is bad. The front end does not have enough camber and looses camber further with body roll. The rear end has too much dynamic movement (bushings allow the back end to move around - too soft) - the rear end "walks around" on the transition to WOT.

Now the suspension tuning 101 you mentioned previous is to solve balance issues! So quite rightly to fix an understeer balance issue you soften front sway and stiffen rear sway.

But if you accept my assertion that the 135i is not too badly balanced in the first place - this is going to hurt the balance further - this is what people have found thru experiment.

So why would people say the stiffening the front sway bar helps handling? What stiffening the front sway does is help limit body roll which helps to limit the bad geometry changes that occur at the front with the 135i. In this instance the driver has sacrificed some good balance to improve bad geometry.

The net effect here is a marginal increase in front grip thru geometry improvements (probably very marginal to nil) and in some circumstances - depending on how the user drives the car - the car will be worse for it - because of upset balance. To confuse the issue further is that some people perceive an improvement because the stiffer sway may improve responsiveness and feel, even though if you went to a race track it may be slower.

I hope that helps - I have tried to abbreviate a subject that could be 100+ pages!.

Nick

[Eyeman]

If sways, etc get too confusing, just get wider front tires and/or add some more camber. At least everyone agrees that helps.