Traction Control

[BB911SC]

I have the option of hooking up traction and launch control with my EFI system. Is it worth the trouble?

[Bill Verburg]

Part of the fun of these cars is the development of the skills needed to use them properly

[BB911SC]

Just thought it might help keep me off the wall during said development! BTW, there is an on/off switch for TC as well.

[Paulporsche]

I think you should do what feels right for you. After all, it's your car. I don't know where you are located, but there may be certain driving conditions existing in your area that would warrant this system. If you enjoy the challenge of installing new systems or items in your car, then that's part of the fun of ownership.

Although, it's tough to beat the enjoyment of driving the cars in the way they were intended to be driven.

Either way (or both) enjoy it.

Paul

[BB911SC]

I live in Holland, it rains quite often.

The car is an SC with a modified 3.6 transplant. Stock suspension (to be addressed as funds permit). I don't think Porsche intended the car to be driven like that either...

[ChrisBennet]

For traction control to work, doesn't the computer need to know if the wheels are slipping i.e. don't you need the sensors in all 4 wheels? I'm thinking of the traction control used in slippery conditions.
Even then, I'm not so sure I'd like a system that could lift the throttle whenever it wanted without a lot of factory development and testing.
-Chris

[Emission]

"Modern" traction control systems moniter each (driven) wheel independantly to check for slip. If detected, it will cut throttle (to both wheels) and apply the brake to the spinning wheel. The brake application causes the opposite wheel (through the differential) to get the remaining power.

I didn't know you could retro that to an older car.

[john_colasante]

Systems like PSM are engineered as part of the chassis of the car. Among other things the PSM system monitors the operating envelope of the car (including yaw angle and accelerations) and limits throttle and/or applies brakes at four corners independantly to keep the car inside the operating envelope and "save your ass". Most guys who don't understand PSM have a knee-jerk reaction to it that it limits your driving enjoyment and reduces the performance of the car - and they turn it off. In reality it is a fantastic system and a competant driver uses it as a tool and drives within it's envelope and extracts the maximum performance from the chassis.

Most aftermarket traction control systems like those built into EFI systems mentioned above work off the ABS system and reduce the engine output if wheel slip is detected. The algorithm is much simpler than something like PSM. Night and day.

[304065]

To say nothing of challenges like a "split-co" when one wheel is in the grass and the other one is on the track. Different coefficients of friction, how will the system react? Now what if you add a limited slip?

I'd use that feature if I had a power boat, though.

[Emission]

On that subject... BMW introduced their traction and stability controls over a period of time starting in the early 1990's:

ASC ~ "Automatic Safety Control " (reduced engine power only)

ASC+T ~ "Automatic Safety Control + Traction" (reduced engine power + applied brakes for traction only)

DSC ~ "Dynamic Stability Control" (reduced engine power, applied brakes for traction, yaw and stability control)

Just the other night I exited an (unfamiliar) circular offramp in the wife's BMW X5. I was coming in too fast, so I hit the brakes a bit harder than usual. Normally not an issue, but there was oil all over the pavement! The tail instantly kicked-out and the "DSC" system responded even before I could countersteer. I slid about three feet closer to the guardrail, but the car never lost control. It was the first time a modern stability system really "saved" me... and I was impressed.

The Porsche "PSM" system is like the current BMW "DSC" system - very advanced!

[BB911SC]

The system uses 4 hall effect sensors to monitor the wheels. It does not use braking, it modifies/cuts fuel and spark to reduce torque when slippage is detected.


Here is what the manual says:

The traction control system, only available on PRO models, is a full 3 or 4 wheel implementation. It will limit the amount of driven wheel spin to any desired slip compared with the undriven wheels. Note that it is not applicable to 4 wheel drive vehicles. To complete sets of parameters are available to allow for differing conditions. These are controlled by a switch on the dash of the car. If no switch is used then the dry settings are used. Besides the wet/dry switch an on/off switch must be fitted on the dash. This switch is not optional as the default for this function is off.

A special data logging mode is available to help set up in single seater cars.

MINIMUM SPEED TO ACTIVATE

Below this undriven wheel speed the vehicle is considered to be stopped and the traction control will take no action.

MINIMUM RPM TO ACTIVATE

Below this RPM the traction control will take no action. Setting depends on engine performance and the desired car dynamics.

MINIMUM THROTTLE TO ACTIVATE

Below this throttle position the traction control system will take no action.

TARGET SLIP PERCENTAGE

The system constantly calculates the difference in wheel speed between driven and undriven wheels. Some slip is beneficial to maximum acceleration, say about 20%. Start line situations are different and require the use of Launch Control. If launch control is active then the traction control will take no action until this has relinquished control over the system.

BALANCE TO FASTER DRIVEN WHEEL

This setting is used to allow some speed averaging across the two driven wheels. For instance in the case of a free differential it should be set to nearly 100%. In a car with a very stiff limited slip differential it should be set to say 25%.

DELAY AFTER START

After the system detects that a car has stated to move it waits this length of time before engaging traction control (unless launch is active see above). There is also a delay before the system considers a car is stopped. This is to allow for the locked brake situation. See General Traction Settings.

EXCESS SLIP TO HARD CUT

This effectively decides how aggressive the cylinder cutting is when slip is detected. If it is too aggressive the car is unstable. Only testing can determine at what level this should be set.

PID FACTORS

These are used if the PID/Servo button is set to PID. Try at 80% Prop and 10% Int.

NOTE That if launch control is activated then traction control will not engage until this has finished operating.