Why is rear end so squirrelly in straight line acceleration?

[dezzracer]

2018 M3 CS. Seems like with all the hi tech performance based electronics loaded into this car (especially the M e-diff) that one would be able to launch this car without the rear moving around side to side so much. With TC turned fully on it's ok because the tires are barely spinning but in MDM mode the rear ends gets so squirrelly side to side. Geez, I can launch my 500 hp 04 Mustang Cobra better and straighter and it has ZERO electronic aids. I don't get it :

[N1rve]

A lot of torque at a low RPM.

[dezzracer]

Originally Posted by N1rve

A lot of torque at a low RPM.

I get it but not more than a supercharged V-8 4 cammer pushing 13lbs of boost :

[Formermercowner]

Originally Posted by dezzracer

2018 M3 CS. Seems like with all the hi tech performance based electronics loaded into this car (especially the M e-diff) that one would be able to launch this car without the rear moving around side to side so much. With TC turned fully on it's ok because the tires are barely spinning but in MDM mode the rear ends gets so squirrelly side to side. Geez, I can launch my 500 hp 04 Mustang Cobra better and straighter and it has ZERO electronic aids. I don't get it :

What's your tire setup?
Size and type of tire?

[G35POPPEDMYCHERRY]

variety of factors including; high torque low rpm, poor DSC, tires, one's lead foot

only modifable thing is your foot/tires; can't floor it at low rpms the DSC always interferes. with tc off you better know how to dirve

[dezzracer]

Originally Posted by Formermercowner

What's your tire setup?
Size and type of tire?

Car is stock with MPSS.

[yayaya]

Did you forget to put it in AWD mode?

[PhatLyfe]

Originally Posted by yayaya

Did you forget to put it in AWD mode?

Priceless

[dezzracer]

Originally Posted by G35POPPEDMYCHERRY

variety of factors including; high torque low rpm, poor DSC, tires, one's lead foot

only modifable thing is your foot/tires; can't floor it at low rpms the DSC always interferes. with tc off you better know how to dirve

I get all that and agree. But I can pretty much feed power into my archaic 2004 Mustang Cobra then floor it through first second and third spinning the whole time and stay pretty much straight. I guess my point is it seems that the fancy active M diff would be able to feed power to each side in milliseconds to help keep the car straighter when accelerating aggressively. It's my understanding this car know's when the steering wheel is straight and communicates with the DSC and M diff as well. Apparently hooking up in this platform (at any speed) in a straight line is not its strong suit. I guess I was just expected more from the electronics in a high-end German engineered performance car. Don't get me wrong, love this car but that part I'm a little disappointed in.

[Sedan_Clan]

Originally Posted by dezzracer

I get all that and agree. But I can pretty much feed power into my archaic 2004 Mustang Cobra then floor it through first second and third spinning the whole time and stay pretty much straight. I guess my point is it seems that the fancy active M diff would be able to feed power to each side in milliseconds to help keep the car straighter when accelerating aggressively. It's my understanding this car know's when the steering wheel is straight and communicates with the DSC and M diff as well. Apparently hooking up in this platform (at any speed) in a straight line is not its strong suit. I guess I was just expected more from the electronics in a high-end German engineered performance car. Don't get me wrong, love this car but that part I'm a little disappointed in.

Honestly it's you, and I don't mean that in any rude or contemptuous manner. I've launched the car plenty of times [with an MT], and I haven't had issues with "squirrelly rear ends".

[behindthen0thing]

I've got a 15 and I don't feel the rear end is squirly on a launch or otherwise. it's easy to break it over but thats different. Maybe you should take it to the dealer and have them double check the software

[dezzracer]

Originally Posted by behindthen0thing

I've got a 15 and I don't feel the rear end is squirly on a launch or otherwise. it's easy to break it over but thats different. Maybe you should take it to the dealer and have them double check the software

I thought about that. Are you guys with DCT saying your cars rear end does not get sideways when breaking the tires loose when accelerating hard while going straight ? Today I floored it at around 35 mph in MDM mode with all other settings in sport. The tires were lit up. The rear end moved from right to left to right before finally hooking up at around 55 mph or so then went straight.

[behindthen0thing]

earlier today i merged onto the autobahn in 2nd gear, i floored it and the rear end was slightly swooshy but smooth, like it will go left and right, but not a whole lot and feels smooth. Also MDM mode, I have GTS diff programmed.
It is a bit wet out but I have winter tires on.

I have floored it at around 35-45 mph in the dry, with cooler tires and it will snap left in that case.
From a launch, it seems to go straight just fine.

[spool twice]

I've learned keeping it in efficiency mode and auto on the DCT that it controls wheelspin better than I can in SPORT and manual mode.

I think it may have to do with how BMW tuned how the boost ramps up on the CS, it will overwhelm its tires (PSS), it wasn't made for PSS originally and you have to drive it understanding it since it the file(s) were designed around PSC2's.

[dezzracer]

Well thanks for the replies. Truly appreciate them. I do understand the concept of overwhelming the tires in a high HP car. I guess my expectations of how well a sophisticated M e diff should work might be too high. Seems it should be able to do a better job keeping the rear end tracking straight than a mechanical locker. I've also tried launch mode twice and both times it just resulted in a Smokey sideways drift halfway into the other lane.

[icegrill]

That's one of my favorite features😬

[dezzracer]

Originally Posted by icegrill

That's one of my favorite features😬

Lol. Yea .. it's fun. It's was also downright violent and scared the crap out of me lol. And I'm familiar with big HP cars. Again tho...maybe my expectations of the electronic wizardry were too high.

[CanAutM3]

I'll echo what some others have said. You just need to learn how to drive it. You said it yourself, it is much tamer in DSC on because the car does the driving for you. For my part, I'm actually happy that the electronics do not interfere too much in MDM and not at all with DSC off. It lets me have the full control over thae car, as a driver's car should be. I personally have no issue with the rear being a bit loose and I actually enjoy it. You can play with the rear end at will, especially now on skinny winter tires . When the rear does step aside you just need to countersteer slightly to keep the heading. You need quick but smooth hands. This car is real pussycat to handle once you get the hang of it. That e-diff is a real jem on how it either opens or locks up at just the right time. And BTW, once the rear tires are spinning, there's very little a diff can do to keep the car straight when accelerating regardless of what fancy electronics are controlling it. Only a TC or DSC system can individually apply brakes and limit power to keep the heading.

I also assume you have the PSS on your car. The CS was really designed to run PSC2, maybe you should try those.

[dezzracer]

Originally Posted by CanAutM3

I'll echoe what some others have said. You just need to learn how to drive it. You said it yourself, it is much tamer in DSC on because the car does the driving for you. For my part, I'm actually happy that the electronics do not interfere too much in MDM and not at all with DSC off. I personally have no issue with the rear being a bit loose and I actually enjoy it. You can play with the rear end at will, especially now on skinny winter tires. When the rear does step aside slightly you just need to countersteer slightly to keep the heading. This car is real pussycat to handle once you get it. That e-diff is a real jem on how it either opens or locks up at just the right time. And BTW, once the rear tires are spinning, there's very little diff can do to keep the car straight when accelerating regardless of what fancy electronics are controlling. Only a TC or DSC system can individually apply brakes and limit power to keep the heading.

I also assume you have the PSS on your car. The CS was really designed to run PSC2, maybe you should try those.

Got it. Thanks. Makes sense when you say that "there is very little you can do to keep the cars heading going straight once the tires are spinning". I'm happy to hear that is a normal occurrence and my car is working properly. Again , I think I had my head wrapped around expectations of a Sophisticated E diff working quick enough to counteract that effect. I'm pretty good at creating problems that are not actually there lol.

[CanAutM3]

Originally Posted by dezzracer

Got it. Thanks. Makes sense when you say that "there is very little you can do to keep the cars heading going straight once the tires are spinning". I'm happy to hear that is a normal occurrence and my car is working properly. Again , I think I had my head wrapped around expectations of a Sophisticated E diff working quick enough to counteract that effect. I'm pretty good at creating problems that are not actually there lol.

That's not quite what I said. I said that there is not much an E-DIFF can do. You, as the driver, can do plenty to keep the car heading straight .

[dezzracer]

Originally Posted by CanAutM3

That's not quite what I said. I said that there is not much an E-DIFF can do. You, as the driver, can do plenty to keep the car heading straight .

Yep I understood that. Thanks for clarifying. The whole point of my thread was about my expectation's of the diff being able to control rear end sideways drift while lighting up the stock MPSS tires. Yours and others explanations make sense. I was almost starting to think my differential was not operating correctly.

[maul3d]

Originally Posted by dezzracer

I get all that and agree. But I can pretty much feed power into my archaic 2004 Mustang Cobra then floor it through first second and third spinning the whole time and stay pretty much straight. I guess my point is it seems that the fancy active M diff would be able to feed power to each side in milliseconds to help keep the car straighter when accelerating aggressively. It's my understanding this car know's when the steering wheel is straight and communicates with the DSC and M diff as well. Apparently hooking up in this platform (at any speed) in a straight line is not its strong suit. I guess I was just expected more from the electronics in a high-end German engineered performance car. Don't get me wrong, love this car but that part I'm a little disappointed in.

I agree with you.