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02-23-2009, 09:24 AM | #23 | |
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02-23-2009, 07:44 PM | #24 | |
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I think the best situation would be to make roll center adjusters that lower the outside contact point of the lower control arms in the rear (where the arm connects to the upright). That would let you run the same static camber (-2.1* or whatever you want), while gain you more dynamic camber in bump. Basically you'd have more camber while cornering and the same camber as before during braking/straights, with something in between for the track-out (putting power down) part of the corner. |
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02-23-2009, 09:03 PM | #25 |
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JEFF - huge kudos for doing this and hope you can continue as I am sure it will continue to be intense with questions to start. I am subscribed and grateful for your .02
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DD & Track Car: 2011 E90 M3 w/Ohlin R&T's, Vorshlag camber plates, Hotchkis swaybars and other mods.
(2008 135i modded - SOLD, 2006 E90 330xi - SOLD, 1995 M3 track car - SOLD) |
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03-01-2009, 10:24 PM | #26 |
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Jeff,
I took my 135i to a local track on Saturday and could use your help with getting the power down on corner exit. The track was Motorsport Ranch in Cresson, Texas. It is not a competitive race track, but rather a local country club track. It is very technical with a nice mix of elevation changes and unique turns. The track is 3.1 miles, but we were using the 1.7 loop which has short straights and either off-camber or flat turns. My car is stock with the exception of camber plates and wheels/track tires. You can image the amount of intervention from the electronic lsd on those off-camber turns as my inside tires get light. And almost as annoying as limping out of corners was hearing my rear pads chirping in machine gun fashion. I was using HT-10 pads and they squeal quite a bit so I could feel and HEAR the brakes being applied. It was a last minute decision to hit the track so I was only running my street setup of about -2 neg camber. I can get more than -3 otherwise. What can I do to get more traction that does not involve installing a LSD? I am considering replacing the front sway bar. Would that help? Thanks, Philip |
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03-02-2009, 03:38 PM | #27 | |
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Yes, adding a stiffer front bar would improve power-down ability (a little). It will keep a little more load on the inside rear tire when cornering. It will also add some understeer to the overall balance of the car. Personally, I would try disconnecting the rear sway bar before I tried adding a stiffer front. That's free and very easy to do: just disconnect one of the sway bar end links. But either way, without a diff a stiffer front bar is going to help. So will disconnecting the rear bar. Did you have DTC/DSC all the way off? I.e., you held the button down for ~4 seconds? On our 135i and on a 335i I drove, after I held the button down for ~4 seconds, ALL electronic aids were off except ABS. I found this to be faster than having the E-LSD interfere... you just have to be very sensitive and careful with your right foot! |
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03-02-2009, 08:03 PM | #28 |
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Thanks Jeff. Just to be clear, won't disconnecting the rear bar also induce more understeer? But as you said, that's a free mod to determine how much of an improvement it will make.
And Yes I disabled all the electronic controls by holding down the DTS button for 4 seconds. It was my understanding that you can't disable the electronic LSD entirely. And as I mentioned above, I could hear the rear brakes pulsating since my pads were squeeling. And at the end one of my run sessions, as I pulled off-line to allow a car to pass, I picked up a ton of marbles. So after cool-down I went out to the service road and did a short 1st gear burn-out to clean the rear tires. I left about a 15 foot stripe with my just my left rear, which then shifted to a 15 foot stripe with just my right rear. Very odd, but I chalked it up to the LSD braking the spinning wheel, which put enough resistance on the car to break the other tire loose. You would think without any LSD I would leave one 30 foot stripe |
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03-02-2009, 10:15 PM | #29 | |
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Hmm... It's odd, I've driven 2 cars (our 135i and a friend's 335i) that spun the inside rear tire easily after holding the TC button down for 4 seconds. There was no electronic intervention. But, then I read online about people saying the E-LSD works even after they hold the TC button down... Not sure how to explain that! To me, it's obvious when the E-LSD is working and when it's not. What you described about the car laying down one strip and then switching to spinning the other tire is exactly what an open diff with a powerful car will do (with no electronic intervention). First one tire will spin, and that will actually cause the rear to step out ever so slightly, and that creates a small cornering force which puts load on the spinning tire; it then regains grip because it has more load on it than the other tire, and the other tire starts spinning. When our car had an open diff, it spun the inside tire easily after holding down the DSC button: |
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03-03-2009, 05:26 AM | #30 |
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Jeff, actually e-diff is only activated when you switch the DSC/DTC off completely (ie. hold button for a few seconds). However, e-diff only works up to a certain point, then it becomes like an open diff. That is my own experience and appears to be consistent with what you are describing. In any case, the way to overcome this is do what we both have done, and that is installing a mechanical LSD.
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03-03-2009, 04:45 PM | #32 | |
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Anyone want to loan me a stock 135i for further, ah, testing? +1. When DSC/DTC are all the way off. |
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03-03-2009, 10:04 PM | #34 |
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Haha, sounds good.
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03-04-2009, 04:26 PM | #35 |
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So Jeff, it sounds like regardless if pushing the TC button for 4 seconds results in E-LSD active or open diff, if I give it enough power, it will spin the inside wheel. Therefore, I think I have two options short of more mods.
1) Be smooth with the throttle to prevent wheel spin which will result in a more controlled attitude, albeit slower 2) Be aggressive with the throttle. I haven't tried #2, but it seems to me that if I don't care about tire wear, and I can keep the car on the track, it might be advantageous to give it as much throttle as possible and let the inside wheel spin. At least my one wheel with traction is putting down more power. Your thoughts? |
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03-04-2009, 05:53 PM | #36 |
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That's interesting.
I've been practicing my drag launches (I would love to practice real racing, but sadly there are no racetracks anywhere near me. stupid island) and with the DSC and DTC (obviously) ALL the way off I always get two stripes about 4-6 feet long from where I launched. What I did notice several times is that the tires would skip, which I thought might be the diff changing action as the loaded side shifted, but the skips were always parallel from the left tire to the right. Maybe the e-diff limits slip up to a certain % of load and then just dumps all the torque? LSD until XX% load bias then it opens? That would explain why it balances torque during a launch where the load bias is pretty low but dumps it when the load bias is high (f.ex: during a burnout, intended or otherwise). |
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03-08-2009, 12:48 AM | #37 | ||
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So, what you want to do is get that inside rear right up to the limit of it's grip, but not exceed that limit. As soon as you add enough throttle to go over that limit, it spins and most of the torque is sent to it (and burnt up in smoke! - rather than pushing the car forward). If you do exceed traction, you want to breath off the throttle a bit to let the tire regain grip. Pretty much like what you described in #1: Be smooth with the throttle to prevent wheelspin. Get that inside rear right up to it's limit. If you exceed that limit you will go slower. Make sense? Quote:
I still maintain that I don't feel any electronic intervention with DSC/DTS all the way off. Thanks for the Q's, everyone |
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03-13-2009, 02:03 PM | #39 |
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Hi, thanks for the helpful thread!
A few questions from darkest Africa: 1. The oil temperature guage doesn't have a "red" zone, only temp graduations. How hot is too hot? 2. I run my 135 on 225/40 18 semi-slick tyres on track days. What tyre pressures would you recommend as a starting point? 3. How will the car behave in DTC mode, i.e. DSC switched off but DTC still on? 4. With the above tyres, would your recommendation of a street / track compromise of -1.7 deg camber front and rear, toe out 1/16 still hold? Thanks in advance for the advice!
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03-16-2009, 05:18 PM | #40 | |
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2) 225w is pretty narrow, meaning that in general you'll have to run slightly higher tire pressure than you would with a wider tire (due to the fact that a narrower tire operates at a higher slip angle to produce the same grip that a wider tire could produce at a lower slip angle, and therefore generates more heat, requiring a higher pressure to lessen heat generation). Aside from that general truth, I need to know specifically which tire you are running to be able to give a recommendation. Also need to know what type of weather you will be running in (cold, hot?) 3) In that mode, the only electronic aids will be ABS and TC (aka the E-LSD or "E-Diff"; it's basically just traction control). In that mode, if you break traction under power coming off a corner, the TC will kick in and brake the inside rear tire. It will cause the car to "hop" a bit, because the TC acts in an 'on/off/on/off' manner. I've only driven a 335i in this mode once on the street for a few minutes, so I can't comment on how it will behave on the track! Maybe someone else can chime in and help me out here? 4) Yes. Remember, if you're worried about tire wear, keep your toe near zero. Racers use toe to adjust the stability and response 'feel' of the car, but street car drivers are usually concerned about tire longevity. Big toe-in or toe-out will wear your tires down rapidly. Hope that helps man, keep the questions coming! |
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03-16-2009, 08:39 PM | #41 | |
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I may be wrong but I believe ABS is ALWAYS on regardless of which mode you're in; I've run autocross laps in both modes (DTC and full "off") and I believe I felt the ABS pulse in both modes. I seriously doubt BMW is going to let anyone turn off ABS in this day and age. I can't speak to the e-diff but in the middle "DTC" mode I believe the car has still intervened a few times when I was getting sloppy (getting? Well, I'm always sloppy but this was a special case) and I believe it was more than just a touch of rear brakes. But it was at a point well after I should have stopped driving and I may be remembering it wrong There's an open autocross practice in a few months where I can probably fit in 20+ practice runs; I'll try to remember to make a point of learning exactly when each mode will cut in. Disclaimer: I could be completely wrong... this wouldnt be the first time |
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03-17-2009, 02:46 AM | #42 |
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The first press turns off DSC and turns TC on. If you hold it down for a few seconds, it turns both off and leaves only the e-diff on.
Based on the above, it sounds like the e-diff has a limit to where it stops operating. I know some ferraris have a similar system that is supposed to be better than a real lsd, but it uses a different set of calipers/disc(s). Not sure how this works, if it's actually better, and how it compares to the 135 system. I also remember lotus engineers suggesting people forego the lsd option on the elises because on most tracks it made no difference in lap times. Might have had to do with the weight. Probably doesn't apply on a 135 since the added weight is a much smaller percentage, but interesting nonetheless. |
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03-17-2009, 10:45 AM | #43 | ||||
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03-17-2009, 04:36 PM | #44 | |
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I don't know if it has any bearing on things, but pretty much the whole of SA is situated at an altitude of about 6000 ft.
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