GT-R RaceROM Traction Control

Introduction

Traction control is a way of maximising acceleration and/or cornering speed by controlling wheel slip (spin) to a predetermined level. It is not a magic fix to enable 1500hp to be put down with impunity, and while it comes with sensible default map values, just like any other aspect of tuning, TC requires proper tuning to get the best results.

The main principle behind slip based traction control is that a tyre provides the best load transfer when experiencing a small amount of slip. Without getting into how, why and things like slip angles, the simple way to look at it, is the ideal amount of slip is the one that gives the best result.

As a simple guide for maximum straight-line acceleration in dry conditions, 10% slip is somewhere close to what we want, and for hard cornering, it’s closer to 2% (when there will be added lateral slip we can’t measure), and will vary between those depending on how hard the car is cornering, the surface, the tyre type etc.

A simplified breakdown of how this works is shown in the below diagram:

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Map List

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Live Data related parameters

·         TC Integral Sum – Total integral component of TC torque reduction

·         TC Proportional – Proportional component of TC torque reduction

·         TC Slip Error – Difference between slip filtered and slip target

·         TC Slip Filtered – Slip after exponential filtering applied

·         TC Slip Raw – Slip as measured

·         TC Slip Target – Target wheel slip

·         TC Torque Reduction – Torque reduction level sent to torque control

·         TC Active – Diagnostic Flags to determine TC operating mode (final logging value is sum of all active states)

TC Integral Gain

Integral correction is added to the proportional correction to give the overall Torque Reduction. The gain value is multiplied by the slip error to give an integral step value, which is added to the existing value of TC Integral Sum. The result is that the integral correction can ramp down and up to try and keep the slip closer to target.

TC Integral Min/Max

These are limits for TC Integral Sum to stop “integral windup”. The defaults can be used for many situations but the max could increased on calibrations that use much lower than default values for TC Proportional Gain.

Negative values of TC Integral Sum mean that TC Torque Reduction is reduced, meaning less traction control interference.

TC Integral Slip Error Activation

Integral correction is set to zero outside of these limits of slip error. This can be used to prevent “integral windup” in situations where slip is uncontrollably high, the proportional element will still be active and at high values of TC Slip Error will often be enough to make TC Torque Reduction be capped by the values in TC Torque Reduction Clamp. If the proportional values are very high then the integral correction will have no effect anyway.

TC Options

Slip Target Cornering Input

This selects the input used on the Y axis of the TC Slip Target Base map. All three options result in absolute values being used, giving the same behaviour turning left or right. “Absolute Yaw” can be monitored by logging G force rotational live data and uses values of a similar magnitude. If you choose “Steering Wheel Angle” you will need to significantly rescale the Y axis of TC Slip Target Base.

TC Overall Enable

Used to enable or disable RaceROM traction control per MapSwitch Mode. The second option only uses the RaceROM strategy when OEM VDC is disabled, however VDC will almost always activate before RaceROM TC.

TC Vehicle Speed Min

Vehicle speed below which traction control is disabled.

TC Slip Target Base

Traction control begins with the slip target. This map outputs the desire slip percentage which the rest of the strategy will target.

TC Slip Target Accel Multiplier

Multiplies the output of TC Target Base using accel as an input. Useful for allowing higher levels of slip encountered at low throttle negotiating tight corners at low speed.

TC Slip Target Multiplier

Used as a way to provided adjustment of slip target based on gear and Mapswitch Mode. As slip is already targeted using vehicle speed, this would typically only need adjusting for different Mapswitch modes. Fine tuning the TC target can be done using a range of 0.8 to 1.2, further custom adjustment can also be achieved using Custom Maps.

TC Slip Target Min/Max

Caps the slip target to a normal range.

TC Proportional Gain

TC Slip Error is multiplied by the output of this map to calculate the proportional component of TC Torque Reduction. At the point that excessive slip is first encountered, the proportional component is most significant while the integral builds up over a (brief) period of time. If you encounter excessive levels of TC Torque Reduction in an on/off nature then try lowering the proportional gain.

TC Shift Ignore Time

The gear axis is DESIRED or NEXT gear (1^st will be removed from racerom) and defines an amount of time from an increase in Gear Desired that traction control will be disabled. This should be extended to disable TC until the next gear is established and natural brief spikes in wheel slip can be ignored.

TC Torque Reduction Clamp

Limits the final value of TC Torque Reduction and can be used to limit the interference on engine power at lower RPM. Can be used to stop excessive torque reduction which otherwise can lead to an on/off TC response instead of a smoother progressive response.

TC Vehicle Speed Min

Vehicle speed below which traction control is disabled.

TC Wheelslip Filter

Filters TC Slip Raw by weighting the latest value to produce TC Slip Filtered which is used in all the slip calculations to determine TC Torque Reduction. Lowering this will increase smoothing of the wheel slip, a sensible range would be 0.1 to 0.6.