What traction control is really doing
When the driven wheels spin faster than the car is actually moving, you're making wheelspin instead of acceleration. Haltech traction control spots that by comparing driven wheel speed against undriven wheel speed. When the difference, called slip, goes past what you've allowed, the ECU cuts a portion of the fuel or ignition events to pull power back until the tires grip again.
It isn't only about launching harder. Stopping a rear tire from breaking loose mid-corner also keeps the car from stepping sideways, so a well-tuned system helps stability as much as it helps traction. And when you want some slide, you can turn it off with a switch or any condition you choose.
Before you start
- Use Percentage Cut. This guide covers the Percentage Cut method on Nexus VCUs and on Elite ECUs running firmware v2.34 or later. It intervenes more smoothly and is easier to tune. Haltech recommends it over the older PID method, and so do we.
- Wheel speed sensors are a must. You need at least one front and one rear wheel speed signal. Sensors on all four wheels give better control. Our guide to how wheel speed sensors work covers the hardware, and using ABS sensors with an Elite covers reusing the factory ones.
- Calibrate the speeds first. Drive in a straight line on a surface where nothing can slip, and every wheel should read the same. If one doesn't, fix its calibration before you touch traction settings. A wheel that reads 3% fast looks like 3% slip all the time.
Turning it on
The setup side is minimal. On the Wiring tab, set the Traction Control Type to Percentage Cut. That's also where you can choose a disable switch if you want the driver to be able to turn it off.
General settings
| Setting | What it does | Our advice |
|---|---|---|
| Driven Wheel Speed Minimum Speed | Traction control won't step in until the driven wheels are faster than this | Keep it above a crawl. Too low and the system can cut power while pulling away, bogging or even stalling the engine. |
| Cut Method | Chooses fuel cut or ignition cut | Ignition reacts slightly quicker but sends unburned fuel into the exhaust. Fuel cut is a touch slower but keeps fuel out of the pipes and off the cylinder walls. We lean toward fuel on street cars. |
| Ramp Out Rate | Only applies to the older PID Control From Vehicle Speeds type | Ignore it with Percentage Cut. It has no effect. |
| Conditional Activation | Lets any ECU channel or condition switch traction control on or off | Useful for things like disabling it in a drift mode or only arming it above a certain speed |
The two tables that do the work
Desired Slip
This table sets how much slip, as a percentage, is allowed before traction control acts. It's a balancing act. Set it too tight and normal cornering or small bumps can trigger false interventions. Set it too loose and the tires will be spinning hard before anything happens.
Cut Percentage
Anything above your desired slip is the slip error. The Cut Percentage table decides what share of fuel or ignition events are cut for a given slip error. The shape should rise: a little slip error gets a light cut, and a lot gets a heavy one.
When you're starting out, go heavier on the cut than you think you need, then back it off step by step until the car drives the way you want. A system that cuts too hard feels flat but is safe. One that cuts too little lets the car get away from you.
Worked example: tuning with a dial
The fastest way we know to dial in traction control is to put the adjustment in the driver's hand. A Haltech 12-position rotary trim module gives you twelve switch positions, and you can use the dial position as an axis on both tables:
- Desired Slip by dial position: position 1 allows 100% slip, which effectively switches traction control off. Each higher position allows progressively less slip.
- Cut Percentage by dial position: position 1 applies no cut, and position 12 steps in hardest.
Now the driver can try a position, feel how the car responds, and click to the next one without a laptop. Once you know which range of positions suits the car and tires, trim off the extremes at either end so every position on the dial is one you'd actually use. A dry-weather track car and a wet street car will settle on very different parts of the table.
Test on a closed course or a drag strip, not a public road. Start with conservative settings and small throttle openings, and log wheel speeds, slip and cut percentage so you can see what the system did.
Troubleshooting
| Symptom | Usually |
|---|---|
| Cuts in a straight line with no wheelspin | Wheel speeds not calibrated to match, or desired slip set too low |
| Bogs or stalls pulling away | Driven Wheel Speed Minimum Speed set too low |
| Tires still spin a lot before anything happens | Desired slip set too high |
| Power comes and goes, car surges | Cut percentage too aggressive for small slip errors |
| Popping or flames from the exhaust on intervention | Ignition cut sending raw fuel into the exhaust. Try fuel cut. |
Traction control FAQ
Can I run Haltech traction control without four wheel speed sensors?
Yes. It needs at least one front and one rear wheel speed signal. More sensors give it a better picture, especially in corners.
Should I use the PID method?
No. Percentage Cut replaced it, and it's the method we set up on every car.
How is this different from torque management?
Traction control reacts to measured slip. Torque management shapes power by time, speed or gear before slip happens. Many drag cars use both. Our article on Haltech's advanced torque management goes deeper, and launch control is the other half of a strong start. Want help setting it up? Book a free consultation.
