Wheel Speed & Traction Control

POINTBY · 06-19-2015, 06:36 PM

Hey guys,

Have any of you experienced traction control engaging "easier" after you swapped wheels/tires from stock?

The reason I ask is because I changed to a square setup today with 275/35/19 front and rear. And when leaving the shop (with brand new tires) I took a corner at decent speed and traction control engaged and pulled back power. And my first thought was that this was due to the front tire being taller and therefore causing a difference in wheel speed.

Or, am I wrong and it was simply because the new tires need a few heat cycles?

Thanks for your help.

CanAutM3 · 06-20-2015, 09:41 AM

A square setup will yield much more DSC/MDM intervention.

My understanding of the DSC system is that it monitors wheels speed and wheel acceleration differences between the four wheels to establish the amount of slip of each tire. This allows the system to anticipate when a loss of traction can occur and take appropriate action. Note that tires are always slipping to some degree, so slip does not equate to loss of traction.

With a square setup, since the rear wheels need to spin slightly faster relative to the fronts for a given road speed, that tricks the DSC system in thinking that there is more rear tire slip than there actually is. So only a slight increase in actual rear tire slip will yield DSC/MDM intervention.

This is why in all the tire threads, I have always recommended to maintain the front to rear diameter stagger ratio as close to stock as possible.

POINTBY · 06-20-2015, 09:45 PM

After some more driving and heat cycles the tires seem to grip better and TC hasn't come on.... so, that might go against your theory.

My question is this - if you're right and the wheel speed difference is causing TC to come on quicker then can the dealer re-flash the ECU to correct this and tell the ECU what the new wheel height is?

The whole point in going square was to make the car more neutral and allow me to rotate the tires for longer life.... so, I'm going to stick with that plan.

CanAutM3 · 06-21-2015, 06:37 AM

Quote:

Originally Posted by POINTBY

After some more driving and heat cycles the tires seem to grip better and TC hasn't come on.... so, that might go against your theory.

My question is this - if you're right and the wheel speed difference is causing TC to come on quicker then can the dealer re-flash the ECU to correct this and tell the ECU what the new wheel height is?

The whole point in going square was to make the car more neutral and allow me to rotate the tires for longer life.... so, I'm going to stick with that plan.

Brand new tires need a little running-in to get to their ultimate grip level. The "mold releasing agents" used in the manufacturing process does make them a little slippery when brand new. So it is very plausible that you had more DSC intervention because of that.

It however does not change my point in my previous post. My track setup is square with rather grippy compared to street tires NT01s. Even Euro MDM gets crazy intrusive when I push the car. DSC off is the only real option.

And I see the same thing with my winter tire setup that is also square, and it is quite worse since they have less grip. Any WOT straight line acceleration at any speed has the DSC light flashing constantly.

POINTBY · 06-21-2015, 04:28 PM

Are you basing your theory on running a square setup at the track?? If so, MDM was lit up like a Christmas tree when I took my bone stock M4 to the track with the factory offset tires. So, what's your point??

Does anyone actually know if the MDM is based on a SET tire dimension??

CanAutM3 · 06-21-2015, 05:29 PM

Quote:

Originally Posted by POINTBY

Are you basing your theory on running a square setup at the track?? If so, MDM was lit up like a Christmas tree when I took my bone stock M4 to the track with the factory offset tires. So, what's your point??

Does anyone actually know if the MDM is based on a SET tire dimension??

Seems like you are not really interested in getting feedback... You dismiss every input.

POINTBY · 06-21-2015, 05:50 PM

Quote:

Originally Posted by CanAutM3

Seems like you are not really interested in getting feedback... You dismiss every input.

It would be great if you would prove your point. Tell us you've seen the actual MDM programming that SETS the tire circumference for front and rear. Otherwise, it could be assumed that a square setup simply causes more yaw and that MDM should be turned off completely when driving spirited (of course this should only be done by advanced drivers).

CanAutM3 · 06-21-2015, 07:08 PM

Quote:

Originally Posted by POINTBY

It would be great if you would prove your point. Tell us you've seen the actual MDM programming that SETS the tire circumference for front and rear. Otherwise, it could be assumed that a square setup simply causes more yaw and that MDM should be turned off completely when driving spirited (of course this should only be done by advanced drivers).

I seriously doubt that anyone will be able to show you proof on the actual programming. Further, I don't believe that the tire diameters are "set" in the programming, but rather that the system expects a given delta between front and rear wheel slip.

I can only share what I have read and my understanding of how a stability system operates and how tire diameters affect it.

My point about DSC/MDM over-intervention is not only when turning, but rather in a straight line. If you get more intervention going straight with a square setup with very sticky tires, in my book that tells me that the programming does not like the square setup.

POINTBY · 07-04-2015, 07:55 AM

Quote:

Originally Posted by CanAutM3

I seriously doubt that anyone will be able to show you proof on the actual programming. Further, I don't believe that the tire diameters are "set" in the programming, but rather that the system expects a given delta between front and rear wheel slip.

I can only share what I have read and my understanding of how a stability system operates and how tire diameters affect it.

My point about DSC/MDM over-intervention is not only when turning, but rather in a straight line. If you get more intervention going straight with a square setup with very sticky tires, in my book that tells me that the programming does not like the square setup.

It doesn't "like" it because the car doesn't understeer anymore... ;-)

I've since had no issue with MDM on the street anymore. So, the tires definitely needed a few heat cycles.

So, when running square I would say that the Euro MDM is a must while on track. And an Advanced driver should be able to turn off all the nannies. I did while at Barber and picked up nearly a second instantly and the car felt GREAT without the MDM intrusion... but I would not recommend turning it off unless you're an Advanced driver with lots of car control skill.

CanAutM3 · 07-04-2015, 09:10 AM

Quote:

Originally Posted by POINTBY

It doesn't "like" it because the car doesn't understeer anymore... ;-)

I've since had no issue with MDM on the street anymore. So, the tires definitely needed a few heat cycles.

So, when running square I would say that the Euro MDM is a must while on track. And an Advanced driver should be able to turn off all the nannies. I did while at Barber and picked up nearly a second instantly and the car felt GREAT without the MDM intrusion... but I would not recommend turning it off unless you're an Advanced driver with lots of car control skill.

How does understeer come into play in a straight line

?

I have been tracking cars for over 20 years. When I started tracking, nannies did not even exist

. So yes, I run mostly with the nannies off when on track. I did turn MDM on to understand how it behaves. Even Euro-MDM is overly intrusive and prevents the full enjoyment of the chassis

.

Good that the square setup works for you

POINTBY · 07-05-2015, 04:09 PM

Who said anything about a straight line???

CanAutM3 · 07-06-2015, 07:49 AM

Quote:

Originally Posted by POINTBY

Who said anything about a straight line???

I did. Do you even bother reading my posts before replying

???

Quote:

Originally Posted by CanAutM3

My point about DSC/MDM over-intervention is not only when turning, but rather in a straight line. If you get more intervention going straight with a square setup with very sticky tires, in my book that tells me that the programming does not like the square setup.

heckyeahbro69 · 07-06-2015, 08:07 AM

My car with us mdm and a square setup intervened quite badly in a straight line, cutting power at like 130mph where I know it's not breaking traction. Euro mdm cured the issue totally. Also, with full dsc on while driving to refuel between sessions, it was also intervening just driving at a normal pace. So yes, the car is set to see a difference in wheel speed from front to back due to the size difference stock. Going to a square setup makes the car think it's spinning the back tires because they have to spin faster for a given vehicle speed. If you REALLY want, I can hook up an isid and drive around displaying wheel speeds with each set of wheels, but that requires a lot of work and I'm off today

06-19-2015, 06:36 PM	#1
POINTBY Private First Class 35 Rep 114 Posts Drives: F82 M4 Join Date: Sep 2014 Location: Marietta iTrader: (0)	Wheel Speed & Traction Control Hey guys, Have any of you experienced traction control engaging "easier" after you swapped wheels/tires from stock? The reason I ask is because I changed to a square setup today with 275/35/19 front and rear. And when leaving the shop (with brand new tires) I took a corner at decent speed and traction control engaged and pulled back power. And my first thought was that this was due to the front tire being taller and therefore causing a difference in wheel speed. Or, am I wrong and it was simply because the new tires need a few heat cycles? Thanks for your help.
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06-20-2015, 09:41 AM	#2
CanAutM3 General 21132 Rep 20,742 Posts Drives: 2021 911 turbo Join Date: Jan 2012 Location: Montreal iTrader: (1) Garage List 2022 Audi RS6 [10.00] 2021 Porsche 911 turbo [10.00]	A square setup will yield much more DSC/MDM intervention. My understanding of the DSC system is that it monitors wheels speed and wheel acceleration differences between the four wheels to establish the amount of slip of each tire. This allows the system to anticipate when a loss of traction can occur and take appropriate action. Note that tires are always slipping to some degree, so slip does not equate to loss of traction. With a square setup, since the rear wheels need to spin slightly faster relative to the fronts for a given road speed, that tricks the DSC system in thinking that there is more rear tire slip than there actually is. So only a slight increase in actual rear tire slip will yield DSC/MDM intervention. This is why in all the tire threads, I have always recommended to maintain the front to rear diameter stagger ratio as close to stock as possible. __________________ Porsche 911 turbo 2021 992 GT Silver Previous cars: M4cs 2019 F82 Limerock Grey / M4 2015 F82 Silverstone / M3 2008 E92 Silverstone / M3 2002 E46 Carbon Black Last edited by CanAutM3; 06-20-2015 at 09:48 AM..
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06-20-2015, 09:45 PM	#3
POINTBY Private First Class 35 Rep 114 Posts Drives: F82 M4 Join Date: Sep 2014 Location: Marietta iTrader: (0)	After some more driving and heat cycles the tires seem to grip better and TC hasn't come on.... so, that might go against your theory. My question is this - if you're right and the wheel speed difference is causing TC to come on quicker then can the dealer re-flash the ECU to correct this and tell the ECU what the new wheel height is? The whole point in going square was to make the car more neutral and allow me to rotate the tires for longer life.... so, I'm going to stick with that plan.
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06-21-2015, 04:28 PM	#5
POINTBY Private First Class 35 Rep 114 Posts Drives: F82 M4 Join Date: Sep 2014 Location: Marietta iTrader: (0)	Are you basing your theory on running a square setup at the track?? If so, MDM was lit up like a Christmas tree when I took my bone stock M4 to the track with the factory offset tires. So, what's your point?? Does anyone actually know if the MDM is based on a SET tire dimension??
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07-05-2015, 04:09 PM	#11
POINTBY Private First Class 35 Rep 114 Posts Drives: F82 M4 Join Date: Sep 2014 Location: Marietta iTrader: (0)	Who said anything about a straight line???
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07-06-2015, 08:07 AM	#13
heckyeahbro69 Captain 518 Rep 629 Posts Drives: m3 Join Date: May 2013 Location: united states iTrader: (0)	My car with us mdm and a square setup intervened quite badly in a straight line, cutting power at like 130mph where I know it's not breaking traction. Euro mdm cured the issue totally. Also, with full dsc on while driving to refuel between sessions, it was also intervening just driving at a normal pace. So yes, the car is set to see a difference in wheel speed from front to back due to the size difference stock. Going to a square setup makes the car think it's spinning the back tires because they have to spin faster for a given vehicle speed. If you REALLY want, I can hook up an isid and drive around displaying wheel speeds with each set of wheels, but that requires a lot of work and I'm off today __________________
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