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02-28-2020, 12:00 PM | #1 |
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Scary mid corner oversteer 135i
Hi guys,
Today I had a scare with my 135i in a right hand "medium sharp" corner going probably around a bit less than 60 miles / 100 km per hour. Suddenly I lost rear traction mid corner without any warning from the car, it was very snappy without any progression at all, it took me totally by surprise. I drive everyday with traction OFF (long press) since with traction ON I feel the car intervenes unnecessarily in corners and confuses me even more. I was probably 100%-90% on the throttle through the corner, that was probably my mistake but I think there is more to it. Luckily I could recover the car and there were no other cars around me in a three lane road. But I had to make 3 corrections (left, right, left) since the car wanted to go in opposite directions back and forth. The road was dry and I drive through that corner every day and this never happened. A few weeks ago I installed MHD stage 2+ (upgraded from running stage 1 for 6 months), Dinan fixed front camber plates, rear M3 subframe bushings along with Eibach lowerings springs (please see my signature with all mods for reference). I know the extra torque and power from the MHD tune will obviously make me power oversteer much easier than before, plus the camber plates have reduced understeer and improved front grip a lot, but now it feels the back has no grip. I was probably over confident thinking the car would still react like it did before the modifications since previously it was really hard to lose traction even when trying to provoke the car. But now that the car is turning in much faster, it feels like there is a certain point in the steering angle that when I go beyond it the car will oversteer immediately without giving it much gas. It feels like the rear wants to overcome or pass the front. I have noticed this before in sharper low speed corners, or going in a roundabout that the car wants to lose traction and rotate the rear much more easily without accelerating too much but this had never happened to me in a medium high speed corner like today. From now on I will be more careful accelerating through a corner due to the power oversteer that the car has right now, but it bothers me that there was no progression in the slide, no warning, it was pretty violent and also I had to overcorrect 3 times to get the car straight again. Is that because the car has no LSD? Could it be an alignment issue? Current settings are: FRONT CAMBER: L -2.39 R 2.22 TOE: L 0.05º R 0.03º REAR CAMBER: L -1.14 R -1.38 TOE: L 0.15º R 0.11º I'm not running run-flat tires, so I was using 35 psi front and back. After this incident I have decided to lower rear pressure to 33 psi, am I correct in thinking this will give more grip in the back? Any other tips or changes I can make? Should I adjust toe? I might try MHd's linear throttle option to aviod all the torque coming immediately mid corner. I'm not a pro race driver but luckily I have some track experience and have driven much more powerful cars and this time luckily I could recover from the slide but this was a good wake up call for me, I was really close to spinning out of the road. Be careful out there!
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CURRENT: 2020 M2 Competition (BSM)
Previous: 2008 135i Last edited by pablom2c; 02-28-2020 at 12:29 PM.. |
02-28-2020, 02:57 PM | #2 |
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you're driving on the street. there was probably dirt on the corner or something... abrupt loss of traction.
Yes a tune will massively increase torque and you'll be power-over-steering much more easily now. Dialing in a bit more rear camber will help keep the rear planted in a turn. More common to see ~1.8* or so out back. |
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Traf94.50 |
02-28-2020, 04:02 PM | #3 |
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Yeah, a bit more rear camber, adjust the shocks to compensate, and don't use full traction off until you 100% understand the car, including finding the limit and being able to control it at/near there using a closed/private road for practice.
You said you have the same PSI front and rear, do you also have the same size tires? And don't forget, your tire pressures will change once the tires get heat in them, check hot pressure once in a while to see how they're doing. |
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02-28-2020, 04:13 PM | #4 |
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Something is worn out in your rear suspension. The upper links are pretty weak back there. Might be time to go with 1M/M3 rear links/bits. Also look at the toe arm(s)...
The bolts for the rear subframe bushings should have been replaced. They are stretch alloy bolts. Double check that they are all tight. You can use a small magnetic to see IF they are steel or alloy. #18... This is the 135i upper arm that is a weak point. Lower arm is the M3 unit. This is the rear suspension toe arm #14 that is also pretty weak. The rubber allows for a lot of play. When you have a tune... it can do weird things to the suspension when you get on it hard mid corner. The M3 rear sub frame bushings help... to get the rear suspension controllable... but still my rear suspension didn't feel 100% until I installed the rear M3 control arms(4) and new tow arms. With a tune and a stock suspension... the rear axle feels like its held in place by rubber bands. It was really a handful. Now I am happy with my upgrades. Good Luck, Dackel
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lab_rat394.50 |
02-28-2020, 06:17 PM | #5 |
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I'd start by adjusting alignment. Max 1 degree difference front and rear. I'd probably go with a half a degree difference since it's a street car.
I might not drive with DSC/DTC full off on the street. Agree with Dack about inspecting rear bushings.
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02-29-2020, 12:32 AM | #7 |
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I don't think less rear tire pressure is the solution to this. That might be an option if you are running a R-comp tire on a track car, but not necessarily true for street tire and street alignment. In your case the rear tire may have lost traction due to some effects of sidewall deformation, which is related to the camber setting and air pressure. The guys suggesting more rear camber are probably right. You have greatly increased your front camber, but running less rear camber than the stock alignment.
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ShocknAwe3234.00 MightyMouseTech4337.50 |
02-29-2020, 01:14 PM | #8 |
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Thanks for all your comments. How can I add more rear camber? The shop tells me that currently that’s the most they can get? I will make them check everything is tight in all the suspension just in case.
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02-29-2020, 04:26 PM | #9 |
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That's all they can get? With my stock rear suspension I can almost get 2.0 degrees?!?
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03-03-2020, 11:32 AM | #10 | |
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Quote:
OP, the 1'er has a very short wheelbase relative to its track width, so it's a pretty snappy chassis even when it's setup well. I run -0.8 degrees of camber in the rear with no issues. It isn't snappy or sketchy at all, and feels very neutral with -2.3 degrees of camber up front. It can get sideways if I flick it into a corner, but it's otherwise pretty stable. Don't drive like that on public roads anyways, it's irresponsible and dumb.
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03-06-2020, 01:15 PM | #11 |
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MHD stage 2, med-sharp turn, 90-100% throttle in a car with smaller tires then what’s optimum for its hp/tq. Some basic improvements in suspension parts and settings isn’t going to to make everything fine and dandy. We watch very well setup race cars push or oversteer all the time and into the weeds or wall.
I wasn’t there but in my opinion, too much throttle for that particular condition. Maybe you went in overconfident with all the nice work you did. Consider yourself lucky that you and your car dodged trouble, we’ve all been there before.
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03-06-2020, 04:38 PM | #12 | |
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In other words, switching out the guide rod and toe arms of the 135i will improve deflection, but switching out the 135i upper arm with an M3 upper arm is largely aesthetic, outside of the slightly lower weight. Ultimately, I agree that locking down the rear end is a good idea with upgrades, but the OP should also expect, even with upgrades, that the rear of this car can get away pretty easily with big torque tunes and traction control turned off. Leave traction control on in public, I'd say. Running over 400 hp/tq gets pretty squirrel-y, especially on stock tire sizes. Last edited by duder13; 03-06-2020 at 04:43 PM.. |
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03-23-2020, 04:35 PM | #13 | |
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First thank for correcting my image mixup. I have to disagree about the 1M/M3 rear suspension bits. After I installed them, the rear of my 135i really felt so much more secure. No more bump steer - mid turn. And the rear just felt solid(and more playful) instead of that feeling being held in place by rubber bands. I really was pleasantly surprised after the install. I also have M3 rear subframe bushings that I installed years ago. I feel that the M suspension bits made a huge difference. Also adding more camber in the front with Dinan camber plates help turn in so much! Dackel
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03-24-2020, 12:25 AM | #14 | |
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03-27-2020, 08:27 AM | #15 |
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I've been in this situation before... First Time I tried long press of the DTC button.
The challenge I think is that this is a fairly short wheel base relative to the power and torque output. The other problem is with the DTC fully on it's way too intrusive to drive and even with 1 step off it still intervenes quite a lot. However for street driving I think safety should be paramount so will just stick to one step off instead of fully off from now on. |
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05-23-2020, 04:53 AM | #16 |
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"But I had to make 3 corrections (left, right, left)"
That means you need to do some advanced driving courses. It can be VERY difficult to catch a sudden rear-wheel slide, but sawing the steering wheel back and forth is not the correct solution. Of course, you must counter-steer (opposite lock) to catch the first slide, but then AS SOON AS YOU FEEL THE REAR COMING BACK, you must CENTER THE STEERING WHEEL. That will settle the car. Wait half a second and correct again if the car is pointing in the wrong direction. If you swing the steering wheel from side to side, the car will do the same. I KNOW, this is not easy, but it is a reflex you need to program into you system. And don't even THINK of touching the brake before the car is settled. |
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