E93 M3 front swaybar - more understeer?

[mmilkov]

Hi folks,

A few days ago I replaced the front swaybar on my 135i with the swaybar from an E93 M3. This is a popular mod in this forum and the general consesus seems to be that it tightens up the front end, i.e. reduces understeer...
I went to an autocross yesterday and the good news is that the car leans less than before. The bad news is that it now understeers significantly more. This was discouraging. To eliminate other factors, I should say that the only thing I have changed between now and previous events is the front swaybar. I am running the same tires (Kumho Ecsta XS, 225/40-18 front, 245/35-18 rear) with the same tire pressures as before.
I am interested to hear other people's opinion. Could it be that those that have replaced their front swaybar with an E93 M3 part think it is better based on the reduced lean, but haven't really reached the car's limits to find out that it understeers more? Should I go back to the stock swaybar? Or maybe the E93 swaybar works only in conjunction with other M3 parts, for example, M3 control arms?
I'd appreciate if people share their autocross / track experience regarding the front swaybar.

Thanks,

Mihail

[pixelblue]

stiffer sway bars increase understeer. that leaning you were getting before actually increases grip and reduce understeer. same with the rear sways. stiffer sways will make you oversteer.

[mmilkov]

Originally Posted by pixelblue

stiffer sway bars increase understeer. that leaning you were getting before actually increases grip and reduce understeer. same with the rear sways. stiffer sways will make you oversteer.

In the stock autocross classes, it is permissible to change either the front or the rear swaybar, but not both. After reading a lot of threads here, it seems that most people replace the front swaybar, not the rear. But why do that if it increases understeer? From the factory the car is set up to understeer, so do people actually want more of it?? Based on my experience (which may not be as isolated as I thought), I would leave the front swaybar alone.

[Dackelone]

Originally Posted by mmilkov

Hi folks,

A few days ago I replaced the front swaybar on my 135i with the swaybar from an E93 M3. This is a popular mod in this forum and the general consesus seems to be that it tightens up the front end, i.e. reduces understeer...
I went to an autocross yesterday and the good news is that the car leans less than before. The bad news is that it now understeers significantly more. This was discouraging. To eliminate other factors, I should say that the only thing I have changed between now and previous events is the front swaybar. I am running the same tires (Kumho Ecsta XS, 225/40-18 front, 245/35-18 rear) with the same tire pressures as before.
I am interested to hear other people's opinion. Could it be that those that have replaced their front swaybar with an E93 M3 part think it is better based on the reduced lean, but haven't really reached the car's limits to find out that it understeers more? Should I go back to the stock swaybar? Or maybe the E93 swaybar works only in conjunction with other M3 parts, for example, M3 control arms?
I'd appreciate if people share their autocross / track experience regarding the front swaybar.

Thanks,

Mihail

I kind of suspected this all along.

One thing that really makes the front suspension work better(and the rear!) is to replace the rear subframe bushings with M3/1M ones. You will forever get rid of that rubber band rear end feel.

[int2str]

Yupp, for autocross you *want* some body-roll.

If you look at most of the swaybar reviews around here, most people don't use them for autocross, but report their findings on the road or the big track. I've been hesitant about the front bars for a long time and think I may finally bite the bullet since I need to keep my rear flatter out of turns. But I'll take the E90 M3 front bars instead of the E93's. Hopefully that'll be a good compromise.

Understeer in your car will be worse also because you're running a staggered tire setup. I did that last autocross during practice and absolutely hated the understeer (even without a front sway bar). Since you probably can't run a square setup and remain in stock, I'd probably bite the bullet and go back to the stock bar.

[Bimmer-Bob]

I know the conventional wisdom, in general, is that a stiffer front bar will increase understeer. But there is some thought that, on a MacPherson strut system like we have, the stiffer front bar helps to prevent the front tires from adopting positive camber under load. I don't know if this is true, but with my M3 front bar (the less stiff E92 bar, mind you), I don't feel like the car plows too much. Admittedly, I haven't run back-to-back tests or anything, and certainly it could be that the flatter feeling is just being perceived by me as "better handling."

Do you have any other suspension mods? I'm on coil-overs and camber plates, so that could be part of it. While I wouldn't describe my car as suffering from "snap oversteer" or anything, with aggressive cornering the back end definitely does step out a bit - usually gets caught by DTC, but still.

I haven't done near enough at-the-limit driving to truly understand how my car behaves at the ragged edge of adhesion. I think it would probably take some time at the track doing back-to-back laps with both bars to know for sure - but I don't see that happening anytime soon (or ever really, let's be honest here).

I suppose I could run tests on successive auto-x heats, but I'm still not an experienced enough driver that I'm confident I would pick up on the difference unless it was very obvious.

[bogart]

More negative camber will counteract the negative affects of a stiffer sway bar.

[Bimmer-Bob]

Another thing to consider is that I'm driving a 128i, which I believe may have a considerably lighter front end.

At the track a few weeks ago, my instructor was a PCA guy who regularly tracks his Cayman. He also tracks his wife's stock 135i, which he had with him that day (she was his other student). Given his experience with those two chassis, I imagine he knows a thing or two about the differences between oversteer and understeer.

Anyway, after a day in both cars (as driver and passenger of each), he told me that he believed my car was much more balanced than his wife's. Now, there were numerous differences between the two cars (weight, mods, etc.) and it could be that he would've liked it even better with the stock bar. My point is only that, in that configuration (I have since swapped coil-overs) he didn't seem to think that it inherently understeered.

I'll also say that the stiffer front bar, since it's keeping the front flatter, makes it seem easier to point the car towards where you want to exit. Of course, that doesn't always translate to forward motion, I suppose.

Finally, I think the bar in the absence of other suspension tuning is probably a net negative. I remember doing the bar early on, because it was cheap and easy to DIY. I naively thought that it would sate my appetite for further modding, but if anything, it lead me to fit coil-overs even earlier than I had planned. It sort of brought out the weakness of the stock suspension, in the same way that my coil-overs have highlighted the wobbly rear subframe bushings. It's a slippery slope, this car - BMW had it tuned for RFT's and soft bushings, and once you go poking around trying to "improve" things you find that it takes quite a bit more to really get the job "done." I'm still not there yet.

[int2str]

Originally Posted by bogart

More negative camber will counteract the negative affects of a stiffer sway bar.

With stock suspension and camber plates likely not allowed, I don't think that's an option.

[mmilkov]

Originally Posted by bogart

More negative camber will counteract the negative affects of a stiffer sway bar.

Suppose I can somehow get more negative camber. In terms of getting more front end grip, will I be better off with the stock swaybar or with the M3 swaybar? I am trying to assess when the stiffer front swaybar actually helps. Is it when combined with rear swaybar? Is it when combined with more negative camber?
And what is the theory behind more body roll leads to less understeer? Could it be that the loading of the suspension with body roll induces dynamic negative camber on top of the static negative camber? I can see this being the case with double wishbone suspensions, but I don't know if the McPherson strut suspension has the property of increased negative camber with suspension loading.

[Bimmer-Bob]

Originally Posted by int2str

With stock suspension and camber plates likely not allowed, I don't think that's an option.

I believe he's saying that the greater negative camber provided by the bar itself outweighs the negatives. Not that the bar contributes to any amount of negative camber statically, but by preventing the shift to positive camber under lateral load.

Theoretically, of course.

[mmilkov]

Originally Posted by Bimmer-Bob

I believe he's saying that the greater negative camber provided by the bar itself outweighs the negatives. Not that the bar contributes to any amount of negative camber statically, but by preventing the shift to positive camber under lateral load.

Theoretically, of course.

The only thing the swaybar does is reduce body lean. If the suspension had a tendency to go to positive camber when the car leans, then I concur with you that the swaybar would help in reducing understeer. However, my actual observation during autocross driving is that there is now substantially more understeer. So your theory that the swaybar counteracts positive camber evidently doesn't hold.
In fact, as I pointed out in the previous post, it may be the opposite. The suspension may provide dynamic negative camber when loaded. A stiffer swaybar prevents body lean and hence loading of the suspension and thus negates some of that negative camber. This leads to understeer. This is just a conjecture on my part based on my observation of increased understeer with the stiffer swaybar. I will let people more knowledgeable on the McPherson suspension geometry to comment.

[bogart]

Originally Posted by int2str

With stock suspension and camber plates likely not allowed, I don't think that's an option.

You can dial in negative camber with stock struts by removing the pin.

Originally Posted by mmilkov

Suppose I can somehow get more negative camber. In terms of getting more front end grip, will I be better off with the stock swaybar or with the M3 swaybar? I am trying to assess when the stiffer front swaybar actually helps. Is it when combined with rear swaybar? Is it when combined with more negative camber?
And what is the theory behind more body roll leads to less understeer? Could it be that the loading of the suspension with body roll induces dynamic negative camber on top of the static negative camber? I can see this being the case with double wishbone suspensions, but I don't know if the McPherson strut suspension has the property of increased negative camber with suspension loading.

If you are on stock suspension, then you will have more grip with the stock sway bar.

The stiffer sway bar works better with stiffer suspension.

When a stiffer sway bar is installed on the stock suspension it causes the weight to transfer faster from tire to tire during cornering. This will cause an even greater "pushing" sensation when cornering. A stiffer front bar also transfers some weight to the rear, also causing more understeer.

A stiffer rear sway bar is only necessary when you are running the stiffer bushings, control arms, and an LSD in the rear.

The largest benefit of a stiffer front sway bar would be when coilovers are installed with camber plates. Dialing in negative camber is the way to allow the sway bar to work correctly by transfering weight to the outside front wheel and rolling over the tire to be in flat, direct contact with the ground or zero camber.

When the stiffer bar is installed on stock suspension, the weight transfers, and the tire rolls over to positive camber, which causes understeer.

Front M3 control arms would give a greater benefit with stock suspension.

Front suspension is McPherson strut and this causes the wheel to move straight up and down during compression, causing no natural negative camber.

The rear suspension is multi-link, which has a natural negative camber built in during compression.

Originally Posted by Bimmer-Bob

I believe he's saying that the greater negative camber provided by the bar itself outweighs the negatives. Not that the bar contributes to any amount of negative camber statically, but by preventing the shift to positive camber under lateral load.

Theoretically, of course.

Sorry for the short response and misunderstandings... the sway bar does not increase negative camber. Front M3 control arms will. Pulling the pin will. Installing aftermarket suspension with camber plates will as well.

I was basically saying that the stiffer front sway bar will work best with aftermarket suspension and negative camber dialed in via camber plates.

Originally Posted by mmilkov

The only thing the swaybar does is reduce body lean. If the suspension had a tendency to go to positive camber when the car leans, then I concur with you that the swaybar would help in reducing understeer. However, my actual observation during autocross driving is that there is now substantially more understeer. So your theory that the swaybar counteracts positive camber evidently doesn't hold.
In fact, as I pointed out in the previous post, it may be the opposite. The suspension may provide dynamic negative camber when loaded. A stiffer swaybar prevents body lean and hence loading of the suspension and thus negates some of that negative camber. This leads to understeer. This is just a conjecture on my part based on my observation of increased understeer with the stiffer swaybar. I will let people more knowledgeable on the McPherson suspension geometry to comment.

Like I said above, the stiffer bar actually causes the tire to positive camber during cornering, which is the feeling of understeer. The stiffer bar also increases the rate at which weight is transfered from tire to tire, increasing the pushing (understeer) sensation.

[mmilkov]

Bogart, thanks for the detailed response.
I did some search and found a good post on swaybar stiffness and understeer here:
http://www.e90post.com/forums/showthread.php?t=531711

"Unlike double wishbone type suspension, the MacPherson strut has an unfavorable camber curve, in that the camber does not increase linearly as the suspension is compressed. So as the car takes a corner and sets, the outside suspension is going to compress past the roll center and will go from a favorable increase in negative camber to start to lose the negative camber. When that happens the front end will lose grip rapidly. One of the solutions to alleviate this problem, is to deploy thicker front anti-roll bars to prevent the outside suspension component from compressing PAST the roll center and start to lose camber."

[fourtailpipes]

Originally Posted by bogart

When the stiffer bar is installed on stock suspension, the weight transfers, and the tire rolls over to positive camber, which causes understeer.

...

Like I said above, the stiffer bar actually causes the tire to positive camber during cornering, which is the feeling of understeer.

great post on a whole. the above is misleading, though. the roll-reducing quality of swaybars will always serve to maintain negative camber (and reduce positive camber). the understeer in this case is not caused by dynamic positive camber, but by a lack of grip in the outside tire, which has been increasingly loaded by the stiffer swaybar (at the cost of the grip you used to get from the inside tire, which is now unweighted significantly, and generating less grip). this inability of the outside tire to cope with it's increased load is generally due to other suspension components which aren't stiffened to match the swaybar (as you mentioned), lack of static camber, or tires that aren't up to the task.

the most important thing, as bogart said, is to upgrade the whole suspension (right down to the tires) to match. stiff parts and soft parts don't work well together (ahem).

[Lubo]

Hey OP. You are not alone in your findings. I took off the swaybar after 2 auto-x events as the car was pushing a lot more. Initially on the street it felt great without the lean and more direct steering response. On the 60 second course it cost me nearly 2

[GaryS]

Originally Posted by mmilkov

"Unlike double wishbone type suspension, the MacPherson strut has an unfavorable camber curve, in that the camber does not increase linearly as the suspension is compressed. So as the car takes a corner and sets, the outside suspension is going to compress past the roll center and will go from a favorable increase in negative camber to start to lose the negative camber. When that happens the front end will lose grip rapidly. One of the solutions to alleviate this problem, is to deploy thicker front anti-roll bars to prevent the outside suspension component from compressing PAST the roll center and start to lose camber."

The advice I got from Dinan is that a little more front anti-roll bar helps a little, but too much more anti-roll bar hurts more than it helps. An e92 M3 ARB is a little more than stock. Your e93 ARB is probably too much.

[mmilkov]

I have a dumb thread browsing question. Now that this thread spreads on two pages, I cannot access page 2! When I click on page 2, I get redirected to page 1 of the thread. How annoying. I've also had this problem when browsing other threads on this forum- I just can't see the last few pages. I tried it with Internet Explorer on my desktop and with Safari browser on my iPhone - same thing.
If anyone knows the answer, please let me know. I won't be able to read your answer on the thread, so PM me

[yandy]

Originally Posted by mmilkov

I have a dumb thread browsing question. Now that this thread spreads on two pages, I cannot access page 2! When I click on page 2, I get redirected to page 1 of the thread. How annoying. I've also had this problem when browsing other threads on this forum- I just can't see the last few pages. I tried it with Internet Explorer on my desktop and with Safari browser on my iPhone - same thing.
If anyone knows the answer, please let me know. I won't be able to read your answer on the thread, so PM me

this is a problem with the Forum software, sometimes it reports an additional page, a couple, maybe more posts too early.. you're not missing anything.

[Qbrozen]

Originally Posted by bogart

You can dial in negative camber with stock struts by removing the pin.

Not to threadjack, but can anyone give me more info on this? I've read something similar here before and I've searched several times using several keywords, but haven't found out what exactly this pin/nipple is or where to find it on the car.

[int2str]

Originally Posted by Qbrozen

Not to threadjack, but can anyone give me more info on this? I've read something similar here before and I've searched several times using several keywords, but haven't found out what exactly this pin/nipple is or where to find it on the car.

Look at the strut towers under your hood. You'll see that the top of the shocks are held in with three screws and there's an additional hole where a pin pokes through. That's an alignment pin that makes sure the shock is always in the same spot. Pull that pin out, cut it off, grind it down, whatever. It'll allow you to move the shock a bit more inwards.

It gives you a tiny bit more camber range. Nothing to write home about though.

[GaryS]

Originally Posted by Qbrozen

Not to threadjack, but can anyone give me more info on this? I've read something similar here before and I've searched several times using several keywords, but haven't found out what exactly this pin/nipple is or where to find it on the car.

http://www.1addicts.com/forums/showthread.php?t=218440