Increased rear camber does reduce straight line torque handling doesn't it?

[BMW135pls]

So I'm planning for my next mod to get the M equivalent front and rear control arm package, and having the alignment tuned for as much possible negative camber up front, and a bit lower than that in back. Only thing I am worried about with this is how launching/straight pulls will handle. Even currently with stock (assumedly, I am not the sole owner of the vehicle, so what mods happened before are unknown to me) alignment, M RSFB, and super sport tires, the back end can sometimes snake while WOT even at speeds of 60+. This is a scary thing to have happen, especially at those speeds, but I do very much like doing straight pulls.

I've been researching alignment theory lately, and trying to get a grasp for how everything works as a full system, so I have a question about that, so I can better understand. To me it can mean one of two things: either increasing negative camber in the rear drive tires AT ALL decreases straight line stability, and my rear end will be even more likely to snake on a straight pull. OR. The alignment works as a system, and since the rear tires currently have more neg camber than the fronts, after the mod/alignment, the front tires will have more neg camber than the rears, so the rear may stabilize more than it is currently, since it's no longer the weak link to straight line pulls.

Any input from more upgraded 1's than mine to increase my understanding?

[BMW135pls]

Actually I think I just had a revelation. I just deduced that since my problem seems to happen ONLY at speeds above 45mph or so, the camber may not be what's causing this, it may be more related to the toe setting, since that's the alignment spec that deals with stability at speed. So do you think that I would be fine at a higher camber setting if I were to make the rear toe-in a bit more aggressive?

[dbronnik]

Not sure what's up with your car -- just measuring your current alignment would be a good start.

FWIW I run -1.9 camber and 0.10" total toe in the rear and don't have any snaking issues over 60 mph.

[The Wind Breezes]

You need an alignment, and possibly new rear suspension parts if they were damaged.

[dcaron9999]

I posted about this behavior a few times, which occurred at any speed. The first thing I hated about my 135i when I brought it to the track for the first time in the summer of 2013 was the snap oversteer tendency of this short wheelbase car.

It got worse with mods to increase power. Hard acceleration in a straight line would kick out the rear end (more so with traction control off on the street). The two major mods I did to eliminate this behavior was installing M3 Rear Subframe Bushings and a Torsen LSD. Problem was solved - there was much less interaction of the BMW e-diff (rear brake assistance) and the DSC.

My alignment specs are -3.0* camber with 0 toe in the front, and -2.2* camber and 1/8" total toe in the rear. Alignment is tailored for the very frequent track lapping events I do, as a participant and instructor at two local tracks. I now make close to 440 lbs-ft of torque, and car goes straight as an arrow. Handling when powering out of turns is neutral and predictable.

See this post specifically about toe settings: http://www.1addicts.com/forums/showp...45&postcount=5

[BMW135pls]

Originally Posted by dcaron9999

I posted about this behavior a few times, which occurred at any speed. The first thing I hated about my 135i when I brought it to the track for the first time in the summer of 2013 was the snap oversteer tendency of this short wheelbase car.

It got worse with mods to increase power. Hard acceleration in a straight line would kick out the rear end (more so with traction control off on the street). The two major mods I did to eliminate this behavior was installing M3 Rear Subframe Bushings and a Torsen LSD. Problem was solved - there was much less interaction of the BMW e-diff (rear brake assistance) and the DSC.

My alignment specs are -3.0* camber with 0 toe in the front, and -2.2* camber and 1/8" total toe in the rear. Alignment is tailored for the very frequent track lapping events I do, as a participant and instructor at two local tracks. I now make close to 440 lbs-ft of torque, and car goes straight as an arrow. Handling when powering out of turns is neutral and predictable.

See this post specifically about toe settings: http://www.1addicts.com/forums/showp...45&postcount=5

Interesting point about the LSD. I already have the 1M bushings installed, so is the LSD the missing link then? Would the 1M control arms help at all, or is that unrelated? So I'm guessing the stock diff has some effects that are not bypassed by turning off the DSC by holding the fun button?

[dcaron9999]

Originally Posted by BMW135pls

Interesting point about the LSD. I already have the 1M bushings installed, so is the LSD the missing link then? Would the 1M control arms help at all, or is that unrelated? So I'm guessing the stock diff has some effects that are not bypassed by turning off the DSC by holding the fun button?

See these posts:

http://www.1addicts.com/forums/showp...69&postcount=6

http://www.1addicts.com/forums/showp...88&postcount=9

http://www.1addicts.com/forums/showp...5&postcount=20


Also, if you press the DTC button once, you will still get one level of nanny assistance, allowing a little more yaw sideways action + reduced e-diff intervention. If you press the DTC button for about 5 seconds (DSC off), this will remove all nannies except for ABS brake control (no more e-diff intervention). Use this "last" mode at your own risk, especially with stock open diff. I use this mode the track with my Quaife LSD diff, once the tires are warm, and only if the track is dry. This last mode also saves you rear brake pads as the e-diff uses rear brakes to control wheel spin...

[The Wind Breezes]

The car won't "snap oversteer" unless you're in over your head. I drive my car at the limit frequently with DSC off and it doesn't do anything I don't ask of it. Yes, powerful RWD cars are not easy to drive...take it easy and don't blame the car unless you have some racing wins under your belt.

[dcaron9999]

Originally Posted by The Wind Breezes

The car won't "snap oversteer" unless you're in over your head. I drive my car at the limit frequently with DSC off and it doesn't do anything I don't ask of it. Yes, powerful RWD cars are not easy to drive...take it easy and don't blame the car unless you have some racing wins under your belt.

Depends on how you use the car ...

As you gain more speed, the 6-speed manual 135i will snap oversteer and be hard to recover on the track when exiting turns with the stock open e-Diff, and traction control nannies partially or fully turned off.

I think it is obvious that on the street, will all the nannies on, this behavior will not show up. But try turning off one level of traction control (DTC mode), and step on the throttle while going straight with a lightly tuned car, and cold tires. The car will go sideways with the stock open-diff. On the track, it gets worse, and you are more exposed to this kind of risk.

An LSD will make the car much more predictable, as it applies power to both wheels. Even if the tires break traction, they do so in syncronized way. It makes the car more stable out of turn on the track, and also while driving agressively on the street. With an LSD, your DSC light hardly ever comes on. You can still go sideways, but the rear end is so easy to recover just by lightly lifting off the throttle.

[E82MSport]

Originally Posted by The Wind Breezes

The car won't "snap oversteer" unless you're in over your head. I drive my car at the limit frequently with DSC off and it doesn't do anything I don't ask of it. Yes, powerful RWD cars are not easy to drive...take it easy and don't blame the car unless you have some racing wins under your belt.

I hear the term "at the limit" often but this really is only relative to driving skill and where you are driving at the time. If you are driving at the limit on the street, this would be vastly different than on a track. I personally wouldn't be doing this on the street, but maybe you're talking about track driving. I really don't know because you didn't provide a point of reference.

When I'm at the track I never disable DSC completely because of the limitations of the stock differential and the lack of predictability with an essentially open differential when all systems are turned off. Another issue is indeed the short wheel base that unless equipped with better alignment, suspension and drivetrain components (bushings, dampers, coils, diff...ect) will only make it more pronounced.

[BMW135pls]

Wow. So in light of things, I've spent a good few minutes researching differences in differentials. From the start, it seems that an open diff is something that a tuned sports car should never have. Apparently, in an open diff, when a tire loses traction, the entire drivetrain loses torque potential to the wheels. In addition to that, it seems that it could actually amplify traction loss, instead of compensating it. The open diff will assign torque to the path of least resistance, the tire that lost traction in this case, whereas an LSD would cut the amount of torque to the spinning tire until it regains traction.

Which brings us back to the topic of the open diff in the 1er. With DSC/DTC bypassed completely (how I normally drive) there's basically the complete opposite of traction control, which accurately describes my issues with momentary traction loss or nervous feeling torque handling. The car only gains traction control with the e-diff software activated at least to some degree, and even then, it's only emulating an LSD anyway, so why not just toss it and put in an LSD? My mind is sufficiently blown. I have to imagine that a proper LSD would help with 0-60 and 1/4M times as well, it's got to be significantly shorter given that you have full torque going to the pavement at all times, as well as ACTUAL lag free mechanical traction control built in that doesn't burn through brake pads.

[The Wind Breezes]

What good is going to the track if you leave DSC on? It's WAY too much of a nanny and won't let you feel the car's natural tendencies when things get interesting. As far as my idea of "at the limit," I'm talking slip angle, tires howling and extreme non-linearity in the controls. My driving skill is advanced and although I do drive the car hard on the street, I save pushing my own limits for the track because when you really push yourself you'll eventually lose control.

Personally, I learned a lot about RWD open diff hooning lower powered cars in the rain. It's very easy to get inside wheelspin and you can really get a good idea of what happens if you slam the weight to the inside with the inside rear wheel spinning hard under power(snap oversteer) and how to manage and avoid it. All it takes is practice and a good imagination for what the car is doing.

Also, for 1/4 and 0-60, you'll benefit WAY more from sticky tires like drag slicks. The LSD won't be as much help drag racing as you'd think.

[BMW135pls]

So one thing I've read in various threads on the 1 series has to do with people pulling the pins on the front shock tower mounts in order to get a little extra camber range on an unmodified car. My question is, if you are installing the M control arms, do the M control arms negate the need to do this, or does it still add more camber even on the M control arms?

By my research, the 135i with front shock pins removed and M control arms installed and without camber plates, the fronts can be maxed at about -1.45 degrees. Is this fairly accurate? And the rears at about -1.75?

[dbronnik]

Originally Posted by BMW135pls

So one thing I've read in various threads on the 1 series has to do with people pulling the pins on the front shock tower mounts in order to get a little extra camber range on an unmodified car. My question is, if you are installing the M control arms, do the M control arms negate the need to do this, or does it still add more camber even on the M control arms?

By my research, the 135i with front shock pins removed and M control arms installed and without camber plates, the fronts can be maxed at about -1.45 degrees. Is this fairly accurate? And the rears at about -1.75?

Pulling the pin would still add more camber even on the M control arms.

Those max camber specs sound about right - are you at stock ride height? If so, you're probably looking at more like -1.25 with just M arms + pulled pins.

[BMW135pls]

Originally Posted by dbronnik

Pulling the pin would still add more camber even on the M control arms.

Those max camber specs sound about right - are you at stock ride height? If so, you're probably looking at more like -1.25 with just M arms + pulled pins.

Yeah stock ride height. Thanks for confirming. Man that is kind of disappointing though, but I guess it's one of those things. Guess I'll have to budget a camber plate at some point to really get those front tires angled out. My front sidewall wear is particularly bad currently, rears seem alright though I guess. 2 months after brand new tires and the front sidewalls are noticeably wearing.

[BMW135pls]

Actually I may have solved at least one portion of my problem. I bet at least some of the issue could be explained by lift throttle oversteer. I have this sort of bad habit where I'll go WOT full 16psi through a few gears then when I get to the top of the last gear I'll let off the throttle suddenly then shift up. I should stop doing that.

[dtla1]

Recently got my aligned done at a well respected, race oriented alignment shop. I've got bilstein b8 and eibach pro-kit springs (lowered about 1"), installed the TRW-M3 front control arms, sawed the alignment pin out since mine looked like it was a stamped bit, and added dinan front camber plates. I've also recently installed whiteline rear subframe bushings, although I don't think that would affect alignment at all.

Tech went ahead and checked my alignment range, I was able to get -3.0* camber on both sides in the front, but we ultimately decided on -2.4*, 0 toe front, -2.2*, 3/32 toe rear. I feel the rear may have a bit more camber than I'd want but we shall see. I have yet to take her out for a fun drive. The tech described these settings as "Semi-race" as in a streetable car, spirited driving alignment.

[Solo_M_Tech]

Ok I have a few observations here....

1. The open e-dif isn't as flawed a design as everyone makes it out to be. The McLaren P1 uses an open diff and electronic compensation. So the system works just fine.
2. Uneasy feeling with the open diff- I track my car alot, and I drive with the DSC completely off. Why? Because the DSC actually makes the car MORE unstable when a high lateral G-load is applied. The light won't flash, because there's no loss of traction, but the DSC will apply the outside front, or rear, brakes to slow the car down. It thinks the car is spinning, when it isn't . I have felt it, my tech felt it, and I just turn it all the way off.
3. IF you have a proper alignment, you will not have any issues getting the power down when exiting a corner. Rear toe has 100% to do with this. I can, in a controlled and intentional manner, control the rear oversteer with throttle application. When track driving I HARDLY get rear traction loss even at WOT mid corner.
4. All of the uneasy feeling with the rear end is bushing, and shock related. Work to tighten everything up with quality equipment and a solid alignment.


5. My tech, and I are researching a way to flash the MDM mode to non ///M cars. He stated the TSC/DSC is the same between ///M and non M cars, just the programming is different. I hope to have an answer to this soon.

[135TX]

Well I'm 99% confident even by holding the traction control Dsc button down for 5,second you are not ever able to turn the e diff completely off.

[Solo_M_Tech]

Originally Posted by 135TX

Well I'm 99% confident even by holding the traction control Dsc button down for 5,second you are not ever able to turn the e diff completely off.

No you can't... and that was part of my point. You also can't completely disable the DSC system either. If you generate enough lateral G's, the car will still interfere, but not as aggressive.

[lowbudgethero]

Originally Posted by ApexResistance

No you can't... and that was part of my point. You also can't completely disable the DSC system either. If you generate enough lateral G's, the car will still interfere, but not as aggressive.

Can you explain this? That's the first I've heard of it, I've never felt any interference other than the elsd with everything off. I think the ABS system does have some sort of brake force distribution, but that's only when braking.

[Solo_M_Tech]

Originally Posted by lowbudgethero

Can you explain this? That's the first I've heard of this, I've never felt any interference other than the elsd with everything off.

The car will apply the front outside brake, when the car senses very high lateral loads, even when the DSC system is completely off. It was programmed that way. The YAW sensor is maxed out with high lateral g's and the DSC defaults to apply the brake to control the car. This is why ///M cars have mdm.