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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Tracking, Autocrossing, Dragstrip, Driving Techniques > How do our cars behave at the limit without LSD?



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      05-14-2012, 12:36 PM   #1
will.c
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How do our cars behave at the limit without LSD?

This question is regarding long sweeping high-speed corners where you have to accelerate throughout, and somewhere mid-corner you reach the limit of adhesion when the tires start to chirp.

(Ex: NJMP Thunderbolt turn #8, for those who are familiar)
I've been at this track couple times, and this corner seemed scariest to me. Exiting turn 7, I progressively go WOT and remain WOT until somewhere middle of turn 8 I slowly let off cuz my balls start to shrivel.

Maybe this is due to the lack of an LSD (or just lack of my skills), but I'm familiar with my car's rate of yaw angle change during a low-speed powerslide being very abrupt. As if I hit a small patch of black ice, the car's rear end does not hesitate to swing out quickly and completely.

My fear is that if I go WOT to the limit at turn 8 (or similar), then one of my rears will lose traction and the car will swing out too quickly to a point I cannot simply adjust the steering to counteract the oversteer.

So here's my question: Are our cars predictable and controllable at the limit during high-speed turns even without an LSD (particularly RWD, all traction/DSC stuff off)? I realize the question is vague, but you know what I mean. For example, I'd consider a 996 unforgiving cuz they tend to spin out even with a slight hint of mid-corner lift in a similar situation.
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      05-14-2012, 01:55 PM   #2
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From someone that has gone off both at T8 and T9:

T8 needs to be treated with respect, it's by far where most people go off. It's a decreasing radius turn that comes at you very fast.

After T7, work up to WOT with a constant right turning radius. At the last possible moment where the turning radius suddenly increases you need to straighten the wheel (yes, I know it's a turn), let the car balance and brake, before turning hard right. Start 2/3rds out and work yourself around the left turn. You want to exit all the way to the left allowing you to treat the following esses as a straight. No brakes after T8 till T1 (after the main straight). Your instructor can walk you through all of this.

T7 -> T8 gradual WOT
T8 -> T9 very light throttle
T9 -> gradual WOT

Without an LSD and DSC/DTC off you'll find yourself spinning the inside wheel a lot. This will translate in a "bog down" effect where you're slowing down more so than expected during turning. This is exactly the opposite from what you're describing, your fear of going off on T8 for example is a matter of throttle modulation. T8 needs little throttle and a good line. Since you're on street tires, you'll have a lot of audible warning (chirp) on how you're doing. Beyond that, it'll mostly depend on your driver skills.

hope this helps
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      05-14-2012, 06:12 PM   #3
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Thanks Peter. So it only gets bogged down rather than rear swinging out? That doesn't sound that bad. Maybe next time I'll grow some balls and try to hear my tire screech at T8.

BTW, how'd you get out at T8 and T9, if you don't mind me asking?
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      05-14-2012, 07:28 PM   #4
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Quote:
Originally Posted by wonho View Post
Thanks Peter. So it only gets bogged down rather than rear swinging out? That doesn't sound that bad. Maybe next time I'll grow some balls and try to hear my tire screech at T8.
The rear can still swing out for a myriad of other reasons but in general, you'll slide a bit without the LSD but with no way to put power down you're not going very far after that.

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Originally Posted by wonho View Post
BTW, how'd you get out at T8 and T9, if you don't mind me asking?
Testing the limits :-)

T8: I wanted to see how late I can brake before turn in, well, now I know :-) Skidded straight out, right over the cone, parked it just a few feet into the grass. In retrospect it was no big deal but at the time it was a major "Oh Shit" moment.

T9: Throttle modulation, testing how much power I can put down throughout the left-hander, I went WOT a split second before straightening the wheel and ended up on the inside grass surface. This was very preventable if it hadn't been for that Chinook helicopter hovering right above, no way to hear the short warning of the StarSpecs before they gave way.

Nothing wrong in testing the limits, just discuss how to safely do so with your instructor and be mindful of traffic. I haven't span/gone 4-wheels off many times but when I did so, my focus was on not spinning back into the track surface, this could get ugly, but rather go off as safely as possible and wait to get waived back in.

Good luck with your T8 challenge! And get that LSD :-)
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      05-14-2012, 10:57 PM   #5
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I've gone off on T9 for the exact same reason.

Will I see you guys there sometime soon? Anything lined up?
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      05-14-2012, 11:50 PM   #6
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Haha nice. I see a trend here. You guys are still in one piece. Maybe going off the track will get me to that next level.

My upcoming events are 5/21 at Lightning, and 6/15-16 at T-bolt. Supposed to meet up with a few other Bimmers not from this forum as well.
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      05-15-2012, 07:30 AM   #7
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I'm starting a thread on Northeast events so we can see who's going when...
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