What torque reduction does
When a drag bike changes up a gear under full power, drive to the tire jumps and the gearbox takes a hammering. Torque Reduction softens that moment. When the ECU sees a shift, it can cut ignition, cut fuel, or pull timing for a short, tunable window, then hand full power straight back.
It is built for drag racing bikes, and it depends on the ECU knowing which gear you are in. You need a working gear position sensor or gear switch set up first; see gear detection. The function also offers an output for a gear shift solenoid.
Wiring tab
Torque Reduction Output is the output that drives your shift solenoid, normally a DPO. Active State sets whether it is normal or inverted. On Low (the default), the ECU grounds the wire when the output is on. On High it does the opposite: grounded when off, open when on.
Torque Reduction tab
| Setting | What it does | Our advice |
|---|---|---|
| Ignition Retard Time Limit | The longest the reduction can stay applied after it starts | A safety ceiling. Keep it only a little longer than your longest intended cut |
| Minimum Throttle Position | Reduction only happens above this throttle opening | Set it high so part-throttle shifts in the pits are left alone |
| Minimum RPM | Reduction only happens above this RPM | Just below your normal shift RPM |
| Output Pulse Width | How long the torque reduction output is held on | Match what your shifter solenoid needs to complete a shift |
| Cut Type | No Cut, Ignition Cut, Fuel Cut, or Fuel & Ignition Cut | Ignition cut is the usual choice and the one we start with |
| Input Select | Whether a gear position sensor or a gear switch detects the shift | Use whichever is fitted and proven reliable |
Ignition cut is the more common method. Fuel cut, or both together, are there if your combination responds better to them. Choose No Cut if you want the shift handled only by the timing retard tables.
The tables
In ECU Navigator, under Torque Reduction, you'll find the tables that shape each event.
Delay Time and Cut Time
Together these two set the timeline of a shift:
- The gear sensor or switch reports a shift.
- Delay Time passes, giving the mechanism a moment before power is touched.
- The reduction runs for the Cut Time.
- Full power returns.
Shift 1-2 through Shift 5-6
Each upshift has its own 3D table setting how much ignition retard it gets. That matters because every gear change is different: the 1-2 shift has the most torque multiplication and is where the tire is most likely to break loose, while later shifts may need very little.
Ignition Offset
This table adds a percentage correction on top of whichever shift table is active, mapped against any two channels you choose. A common use is extra retard when air temperature is high, or less when conditions are cool and grippy.
How we approach tuning
- Get gear detection rock solid first. A missed or false gear reading makes everything else unpredictable.
- Start with short cut times and mild retard, then add more only if logs or the rider show the shift is still harsh.
- Tune one shift at a time using its own table, starting with 1-2.
- Watch RPM and driveshaft or wheel speed through the shift in your logs, not just the rider's feel.
For cars rather than bikes, look at flat shift, torque management and traction control, which cover similar ground in different ways.
Troubleshooting
| Symptom | Usually |
|---|---|
| Nothing happens on a shift | Below min throttle or min RPM, Cut Type set to No Cut, or gear detection not seeing the change |
| Shift still harsh | Cut Time too short, or not enough retard in that shift's table |
| Bike bogs after the shift | Cut Time too long, or the retard time limit is letting reduction hang on |
| Shift solenoid doesn't complete the shift | Output pulse width too short, or Active State wrong for your wiring |
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