Floaty feeling under hard acceleration / poor traction / MDM

grabbou · 04-20-2021, 03:23 PM

Hey,

I am trying to figure whether this is a normal RWD behaviour, or my KW V3/tires/alignement setup needs to be tweaked.

I am running KW V3 "recommended" settings, 265/30/20 Michelin PS4S tires on the front, 295/30/20 Michelin PS4S tires on the rear (4.5mm thread on the inner side), alignement done at the dealership, everything stock, except rear camber is at -2.

The tests were done on both flat and "bumpy" roads, although the surface quality is rather on the poor side (not really sticky).

Under heavy acceleration with traction control = ON or in MDM mode, it feels like the front of the car wants to go turn left or to the right. I need to operate a lot with my steering wheel to keep it going straight. This feeling is smaller on a better surface with more traction and dramatic on a really poor road conditions. Sometimes it happens before the rear looses traction - the front starts pulling to a different side even before the traction control light appears.

FWIW, nothing of the above happens under mild acceleration / comfort mode.

I would understand the rear end of the car going sideways when loss of traction, but the feeling of the front being pushed to the side is really weird. Overall, it feels more like floating. I don't really like this experience, I would expect the car to be well planted.

Having recently driven the new M4 generation (demo car), I didn't experience any of this.

-

Now, the question: is this caused by a wider rear tire or a different (non-stock) wheels widths and offsets? Any tips to reduce this behaviour?

hC1001 · 04-21-2021, 08:40 AM

Hows your alignment? It could possibly be your front toe setting. More toe in keeps the car tracking straight because the wheels are like this: / \

NYG · 04-21-2021, 11:34 AM

I'm assuming you track the car so before I answer, it doesn't make sense to run -2 in the back with the stock front (mine was -1.2/-1.3). You need camber plates for the track.

It's hard to know why this is happening if you have MDM or TC on. Road curvature will induce slip on one side faster than the other so MDM/TC will pull power from there if it senses enough slip.

If this happens with DSC off + steering on comfort and you're confident that you're running toe-in at the front then it may be lack of front caster.

grabbou · 04-21-2021, 03:12 PM

I have scheduled alignement and will post pre and post settings to see whether any of these are off. The last time alignement was done was a while ago.

I have recorded some videos in MDM mode demonstrating how the car becomes "unstable" under loss of traction (which happens less with traction, but the rear is still a bit wobbly, which I believe might be due to LSD). I will post them later today.

04-20-2021, 03:23 PM	#1
grabbou Enlisted Member 3 Rep 47 Posts Drives: 812SF, E46 M3, S560 Coupe Join Date: Aug 2017 Location: Europe iTrader: (0)	Floaty feeling under hard acceleration / poor traction / MDM Hey, I am trying to figure whether this is a normal RWD behaviour, or my KW V3/tires/alignement setup needs to be tweaked. I am running KW V3 "recommended" settings, 265/30/20 Michelin PS4S tires on the front, 295/30/20 Michelin PS4S tires on the rear (4.5mm thread on the inner side), alignement done at the dealership, everything stock, except rear camber is at -2. The tests were done on both flat and "bumpy" roads, although the surface quality is rather on the poor side (not really sticky). Under heavy acceleration with traction control = ON or in MDM mode, it feels like the front of the car wants to go turn left or to the right. I need to operate a lot with my steering wheel to keep it going straight. This feeling is smaller on a better surface with more traction and dramatic on a really poor road conditions. Sometimes it happens before the rear looses traction - the front starts pulling to a different side even before the traction control light appears. FWIW, nothing of the above happens under mild acceleration / comfort mode. I would understand the rear end of the car going sideways when loss of traction, but the feeling of the front being pushed to the side is really weird. Overall, it feels more like floating. I don't really like this experience, I would expect the car to be well planted. Having recently driven the new M4 generation (demo car), I didn't experience any of this. - Now, the question: is this caused by a wider rear tire or a different (non-stock) wheels widths and offsets? Any tips to reduce this behaviour?
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04-21-2021, 08:40 AM	#2
hC1001 Captain 591 Rep 987 Posts Drives: E36 M3, F80 M3 Join Date: Nov 2019 Location: Brooklyn, NY iTrader: (4)	Hows your alignment? It could possibly be your front toe setting. More toe in keeps the car tracking straight because the wheels are like this: / \
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04-21-2021, 11:34 AM	#3
NYG Brigadier General 10691 Rep 3,675 Posts Drives: Audi R8 Join Date: Feb 2017 Location: Brooklyn, NY iTrader: (0)	I'm assuming you track the car so before I answer, it doesn't make sense to run -2 in the back with the stock front (mine was -1.2/-1.3). You need camber plates for the track. It's hard to know why this is happening if you have MDM or TC on. Road curvature will induce slip on one side faster than the other so MDM/TC will pull power from there if it senses enough slip. If this happens with DSC off + steering on comfort and you're confident that you're running toe-in at the front then it may be lack of front caster.
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04-21-2021, 03:12 PM	#4
grabbou Enlisted Member 3 Rep 47 Posts Drives: 812SF, E46 M3, S560 Coupe Join Date: Aug 2017 Location: Europe iTrader: (0)	I have scheduled alignement and will post pre and post settings to see whether any of these are off. The last time alignement was done was a while ago. I have recorded some videos in MDM mode demonstrating how the car becomes "unstable" under loss of traction (which happens less with traction, but the rear is still a bit wobbly, which I believe might be due to LSD). I will post them later today.
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