Does the limited slip do annything when DSC is on?

[Thik]

The idea of a LSD is when one wheel loses traction, the differential sends power to the other wheel so the one wheel doesnt spin endlessly and more power is put to the ground.

However with traction control on, any wheel spin will be detected by the computer and it will brake to reduce spin. So what good is the lsd when traction control is on?

[Longboarder]

There are different levels of intervention. Normal mode will allow for not much wheel spin, yaw, etc and significantly hinders performance. MDM allows for more slip and a lot of the US guys get coded for Euro MDM which is less intrusive that MDM and allows for even more slip.

If I try to mash the throttle in 1st gear from a standstill with dsc off it will just spin the tires violently. With Euro MDM I can just mash the throttle and take off hard.

Trust me the m3 LSD is working hard. Not just straight line but in the corners as well. I tracked a 335 for a while the eventually got a wavetrack LSD and the difference was dramatic.

[dragonsi]

Are you serious? It's a mechanical component, take a drive in a 335i and you'll immediately notice a difference.

[Hujan]

What they said. We don't have an electronic differential. It's a mechanical part that is always active. It's designed to allow a certain amount of slip in varying conditions compared to a completely open differential. It has nothing to do with DSC.

[Thik]

Originally Posted by Hujan

What they said. We don't have an electronic differential. It's a mechanical part that is always active. It's designed to allow a certain amount of slip in varying conditions compared to a completely open differential. It has nothing to do with DSC.

I know it's a mechanical part. I can totally understand when the DSC is off, one wheel slipping will mean the LSD transfer power to the other wheel.

But with the DSC on, when one wheel starts slipping, the computer cuts off power and apply brakes. So how would the LSD transfer power to the other wheel?

[dogbone]

Originally Posted by Thik

But with the DSC on, when one wheel starts slipping, the computer cuts off power and apply brakes. So how would the LSD transfer power to the other wheel?

I can tell you from looking at a bunch of AIM Solo DL data, Euro-MDM still allows the inner/unweighted wheel to spin on acceleration, as long as the car isn't getting out of control. So the diff can still have something to do----BUTTT----it doesn't have nearly as much to do as it would with DSC-off because MDM holds back the engine's power.

I've made a picture for you to illustrate. This chart is the "Off-Ramp" corner at Buttonwillow. Off-Ramp is a sharp, right turn that goes up hill and then even gets a little off-camber. It is a tough corner. Euro-MDM is ON in this chart, and we'll see proof of that.

In the pic below:

Dark Blue line - Left Rear Wheel speed
Red Line - Right Rear Wheel speed
Purple Lines - Front Brakes being applied (I've made the left and right the same color for simplicity)
Light Green Lines - Rear Brakes being applied (I've made the left and right the same color for simplicity)
Orange Line - Driver applying brakes
The Numbers at the bottom of the chart show how many feet I am down the track.

The first thing to look at is the Red Line. Notice how the Right Rear Wheel spins up faster than the left several times while accelerating up the hill. This makes sense. We are in a sharp right hand turn. The left side of the car is loaded. The right side of the car has less weight. When I get on the gas, the diff is open and it sends power to the wheel with less traction. We can see the Right wheel spinning up faster than the Left several times. And we can also see that there is NO Light Green line showing any activity at this moment. This means that the Traction Control system is not engaging any rear brakes while the right wheel spins up. Interestingly, we can see that the car is applying Front brakes all on it's own thanks to the Traction Control system. I am not pressing the brakes at this moment. If I was, you would see an Orange line pop up like it does around 2900 feet.



So, I would say the power of the engine being held back is the bigger restriction on the diff's action than potentially braking a spinning inner/unweighted wheel----at least in most cases. In my AIM data, I don't really see MDM brake the rear wheels much while full-on accelerating. It happens when there is an elevation change like you can see at around 2600. That spot of the track has a hump in it and MDM is cautious there. It does brake the fronts quite frequently though. And it will brake the rears in high speed rounders.

Also, looking at charts like these, it seems that the M3's stock diff isn't lightning quick about locking regardless of whether DSC is on or off. My stock diff was done, so I have a new (OS Giken) diff and the data seems to show that it locks quite a bit quicker than the stock unit.

[bigjae1976]

Our M3s are street cars. Not sure if its a federal mandate but every new car I've been in (I rent a lot of cars too) has traction control. So DSC is for the soccer moms driving in the rain or teens doing stuff like this...

The LSD is for off the street shenanigens with DSC off. And boy is it fun!

[OneSickM]

Originally Posted by Thik

I know it's a mechanical part. I can totally understand when the DSC is off, one wheel slipping will mean the LSD transfer power to the other wheel.

But with the DSC on, when one wheel starts slipping, the computer cuts off power and apply brakes. So how would the LSD transfer power to the other wheel?

I agree with you. I never felt LSD kicking in when DSC is ON. and yes I drove 335i for 2 years. Unless you turn off DSC off, you wont feel LSD kicking in..