What torque reduction does
The Nexus Torque Reduction function is aimed at drag racing motorcycles. When the rider (or an air shifter) changes up a gear, the ECU briefly takes some torque away so the gears can change cleanly without backing off the throttle. It does that with any combination of three tools: cutting ignition pulses, cutting fuel pulses, and retarding ignition timing. There's a separate 3D retard table for each gear change, so you can treat the 1-2 shift differently from the 4-5, and there's an output available to fire a shift solenoid.
The ECU has to know when a shift is happening, so this function needs a gear position sensor or a gear switch. Without one, it can't run.
The settings
| Setting | What it does | Our advice |
|---|---|---|
| Input Select | Which input tells the ECU a shift is happening: Gear Position Sensor or Gear Switch | Match whatever is fitted to the bike |
| Cut Type | No Cut, Ignition Cut, Fuel Cut, or Fuel & Ignition Cut | Ignition cut is the usual choice. It acts fast and recovers fast |
| Ignition Retard Time Limit | The longest torque reduction can stay active after it triggers | Keep it short. It's a safety cap, not the shift length |
| Minimum Throttle Position | Throttle needed before it will act | High enough that part-throttle shifts in the pits don't trigger it |
| Minimum RPM | Engine speed needed before it will act | Below your lowest real shift point, above anything you'd see while staging |
| Output Pulse Width | How long the torque reduction output (for example a shift solenoid) is driven | Long enough for the shifter to complete its stroke, confirmed in logs |
Picking a cut type
Ignition cut drops spark events while fuel keeps flowing, so power comes back the instant the cut ends. Fuel cut removes injection events instead, which some builders prefer on setups that don't like unburned fuel in the exhaust. Fuel & ignition cut does both for the hardest cut. No Cut leaves only the timing retard from the tables, which suits setups that just need the edge taken off.
Our starting approach is conservative: ignition cut with modest retard in the shift tables, then add more only where the logs show the chassis or driveline needs it. Too much reduction costs time; too little and you'll see wheelspin or a harsh shift after the change.
Tuning tips
- Log gear, RPM, throttle and the torque reduction state together. You want to see the reduction start with the shift and end as soon as the next gear is engaged.
- Tune each shift on its own table. Lower gears usually need more help than the top shifts.
- Check the gear input is rock solid first. A noisy gear signal can trigger false shifts.
Related settings are covered in shift, cut time, ignition offset and torque reduction wiring.
