How Racelogic Traction Control Works
The system works by monitoring the speed of all four wheels using the ABS system or specially fitted sensors. When wheelspin is detected the engine power is reduced, by cutting a single injector pulse or a spark, until grip is resumed. This occurs in a thousandth of a second, and appears to the driver as a slight miss-fire with no loss in acceleration.

Maximum acceleration is achieved by limiting the slip between the tyre and the road. The point at which a tyre is just beginning to slip against the road gives the maximum coefficient of friction value.

From the graph above it can be seen the maximum coefficient of friction (µ) occurs at a slip between tyre and road of 10% when dry, and around 5% when wet.

Maintaining this level of slip is inherently difficult, as the grip levels drop off significantly above these levels, meaning the balance between too much wheelspin and not enough power is very fine.

To drive the car and search for these levels of slip is very difficult, the moment the wheels start spinning too much (and how do you feel what is too much?) the power has to be reduced (by what amount?).

Top rally drivers have a good feeling for this limit, but they still tend to stay on the side of caution, and modulate the wheelspin between 10-20%, as this will still achieve 90% of the available traction. The closer to 5 or 10% slip, the higher the chance of reducing the power too much, and hindering acceleration, but also the closer you are to using 100% of the available traction.

The main reason for this is the response time of a human being. The fastest human reaction to a sense stimulus is 1/10th of a second, and the fastest acting throttle reacts in around the same time. This means there is a 2/10ths of a second lag between the wheel reaching a critical slip level, and the driver being able to change the amount of power being applied. This is why really good drivers tend to drive between 10 and 20% slip, to give a margin of safety should the tyres suddenly find a little more grip, causing the wheel to stop spinning completely.

Less experienced drivers will tend to allow 20-30% or more slip, again to maintain wheelspin rather then let the car 'bog' down, thus limiting their grip levels to around 85% of their maximum.

With the advent of fast reacting electronics on cars, this problem has been tackled with Traction Control systems. In race cars, Traction Control Systems have two functions, number one is to maintain the precise level of slip that will give close to 100% of the available grip, and number two is to maintain stable cornering. These two functions are linked, but require slightly different approaches.

The speed of reaction of a race Traction Control System is critical in maintaining a precise level of slip. The electronics themselves can react within a thousandth of a second, but to remain effective the engine power has to be quickly, and precisely controlled.

In road cars Traction Control normally relies on two methods of reducing the speed of the spinning wheel, brake application and throttle intervention. Brake application is a very effective and quick way of reducing the speed of a spinning wheel (almost unusable in a race situation - more later) but the accompanying throttle intervention is mechanically slow, and will also only reduce the airflow, which takes some time to become effective. On a road car the Traction Control System plays a third role, one of safety, in this role the level of slip is reduced to zero, and held there. This results in a very stable car, but one which will not accelerate at it's maximum potential at all times.

Race Traction Control Systems rely on much more precise, and faster acting ways of reducing power. The first method is shutting off fuel to the engine, and the other is cutting out the spark. Both methods have exactly the same high speed modulation ability, but the spark cutting system will happen potentially one cycle earlier. The magnitude of difference in reaction times between spark cut and fuel cut is negligible compared with the difference between throttle actuation and spark/fuel cut. (See fuel cut and spark cut below)

The Traction Control System then comes down to the interaction between the information from the wheel speed sensors and the level of power reduction applied. A good system would be capable of maintaining a level of slip that is adjustable depending on conditions.

Many factors affect the ideal level of slip, wet / dry conditions, speed of the vehicle, lateral g-force (cornering), tyre compound, tyre pressures etc. Ideally the driver should be able to dial in a base level of slip that takes into account weather and tyres, and the system should adjust automatically for speed of the vehicle and lateral g-force.

When cornering, the system should reduce the amount of slip available, to prevent lateral slip from occurring, and vary this amount depending on the speed of the vehicle. At high speed, low grip situations, this slip should be around 1-2% to maintain forward momentum, and at low speed high grip situations, this can be much higher.

Fuel Cut
The idea of cutting fuel to an engine sets alarm bells ringing in engine builders, as they all know of the potential disaster of a high revving race engine running lean. Running in a lean combustion mode will elevate in-cylinder temperatures very rapidly, the denser the air/fuel charge, the more heat the lean burn can generate. Therefore it is vital that a fuel cut system will not cause a lean burn.

The simplest way of preventing a lean burn is to remove more than 50% of the fuel from the pulsed delivery. A mixture will only ignite if the air/fuel ratio is within a tightly defined window, look at the efforts being put into making lean burn engines fire on very low air/fuel ratios (1:20 or more). Removing more than 50% of the fuel will cause an air fuel ratio of over 1:25 and will result in a complete miss-fire, with the unburned fuel passing out through the exhaust valve. Even if a high air/fuel ratio did manage to ignite, the energy available from the amount of petrol injected wouldn't be enough to elevate temperatures significantly. Of course the ideal system will remove 100% of the pulsed fuel delivery, allowing the cylinder to take a gulp of fresh air, and the in-cylinder temperature would remain virtually unaffected.

Prolonged fuel cut on one particular cylinder would cause scavenging of the petrol lining the inlet tracts, and when the next full fuel pulse arrived, it would be partially reduced in quantity by the re-wetting of these tracts. Therefore it is often important to manage a rotation of the cylinder cutting to prevent this situation from occurring.

Spark Cut
Cutting the spark to an engine will stop any chances of a weak mixture occurring, but it carries it's own potential problems due to a large quantity of unburned fuel travelling through the cylinder and out of the exhaust. This petrol can remove some of the oil lining the inside of the cylinder, and pass it thorough the exhaust, again this only becomes a problem if the fuel to one particular cylinder is cut for an extended time. The best way to overcome this is to rotate the order in which the cylinders are cut.

The unburned fuel in the exhaust will have a catastrophic affect if there is a catalytic converter in the exhaust, as it will try to convert the unburned fuel to harmless elements, effectively burning the mixture. This causes the catalytic converter to heat up very rapidly, reaching temperatures in excess of 1000°C, and possibly melting down completely. Thus prolonged spark cut is not recommended for catalytic equipped cars.

Data Logging
The Data Logging option allows the unitto permanently record the wheelspeed, engine revs and tractioncontrol activity. The resolution of the information can be varied according to the length of each run, ensuring that maximum accuracy can be achieved.

With the Traction Control software Data Logging allows two runs to be compared and overlayed so the system can be optimised, and driving styles analysed.

Fitting
If the car has fuel injection and ABS then the fitting can be carried out by any competent Auto-Electrician or an electronically competent mechanic or garage. You do not necessarily need a laptop computer or any special tools.

If the car doesn't have ABS then you will need to fit four wheel speed sensors to the vehicle, which involves fabricating brackets and adjusting the sensors.

Woodhouse can supply and fit your Racelogic Traction Control system. Please contact us to get your system setup today!

Follow the links below for specific vehicle installations. These are threads from owner's club forums and can provide useful guidelines, but please be aware that Racelogic accepts no reponsibility for damage caused to owner's vehicles as a result of using this information.

• Nissan 200SX S14 / S14a
• MR2 Turbo MKII
• Supra MKIV

It is activated by pressing a button on the dashboard when the car is stationary. This will bring in a secondary rev-limit (for example 4000 rpm).

The throttle can be fully depressed without over-revving the engine. The car is put into gear, the throttle floored, and then the clutch is engaged, whilst the launch control system controls the wheelspin and revs for the perfect start.

On a turbo car, if the launch control is active, and full throttle is given for two to three seconds, the boost pressure will build up before the clutch is released, resulting in stunning off-the-line performance.

The launch control rev limit can be programmed via a laptop computer or by a combination of presses on the launch control button. This is done by pressing it once, and then once again but this time holding it in and raising the revs to the desired level, then the button is released, setting the new rev limit to this level. This makes it very easy to re-program the launching revs just before a start if conditions suddenly change.

There are various parameters you can tune if you want to get the last little bit of acceleration out of the system. You can have two switchable levels for wet and dry, the level of wheelspin at which the system swaps from Launch Control to traction Control can be adjusted, and on the professional system you can even switch to a lower limit once the car starts to move.

Click here to download an AVI movie of a BMW Z3M doing a launch start. (866Kbytes)

Click here to download an MPG of a Supra drag racing car using launch control. (Please note: 12.5mb)

Full Throttle Shift
The full throttle gearshift system is activated by a switch fitted to the clutch pedal, either a hydraulic switch or a mechanical switch. Once the clutch is depressed, the system automatically drops the engine revs down by using a momentary rev-limit, allowing the next gear to be selected without lifting off the throttle. Because the throttle is always fully depressed, the engine is instantly back on full power, and on a turbo car the turbo is still producing boost. Tests have shown up to 0.1 seconds can be gained per gearchange.

Spark Cut
The Spark interface unit allows Racelogic Traction Control to be fitted to a car without electronic fuel injection. The system can drive up to two separate coils, and interrupts the original signal going to the coil, and allows the Traction Control system to selectively miss-fire set cylinders.

The unit will automatically cycle the cylinder cut so the plugs do not foul. The more reduction in power that is requested from the Traction Control unit, the more cylinders are cut. The effect is from a mild miss-fire, through a soft-cut rev-limit to a total cut.

Wheel Speed Sensors
The exact method used to locate and trigger the wheel speed sensors is absolutely critical to the correct operation of the Traction Control System. There are a number of different ways to construct the pick-ups, the easiest being the bolt detection method. The TC system needs a minimum of four pulses per revolution, there is no maximum. There can be a different number of pulses from front to rear, but not between left and right across the same axle. Eg. 34 teeth at the front and 4 teeth at the rear is fine, 34 left front and 4 right front will not work.

The sensor works by detecting the presence of a ferrous trigger point. Mount the sensor at a gap of 1mm from the hub bolts / disc bolts. The head of the bolt must be flat, a cap head will cause a double trigger as it picks up each side of the head. Turn the hub slowly and check the gap never grows bigger than 1mm from any of the bolts. The sensor must be rigidly mounted so no large vibrations occur that will move the sensor head more than 0.8mm away from the reference points and the head must be at 90° to the surface. If a sensing plate / disc is used, it must not be warped or mounted at an angle that would cause the distance between the head and disc to change by more than ±0.5mm. The material used for the reference must be of a ferrous type, if in doubt, check to see if it attracts a magnet. The reference can be painted or plated.