What the table controls
When a shift is requested, the Nexus turns on the outputs that move the shifter, whether that's air valves on a pneumatic shifter or another actuator. The Shift Duration table sets how long those outputs stay on. It's the ECU's answer to "how long do I push before I let go?"
Regulated air: keep it simple
If your air supply runs through a regulator, the shifter sees the same pressure every time, so it takes the same time to move. Most cars in this situation use a single value in the table. There's no need to map anything.
Unregulated air: two options
Without a regulator, pressure falls as the tank is used and recovers as it refills. Lower pressure means a slower shifter, so a time that works at full tank may be too short near empty. You can handle that two ways:
- Play it safe: set one long enough time that shifts complete even at the lowest pressure you'll ever see.
- Map it: put air supply pressure on the table's axis, so the duration is shorter at high pressure and longer at low pressure. You get quick shifts when the tank is full and reliable ones when it isn't. This needs a pressure sensor on the air system.
Too short vs too long
| Duration | What happens |
|---|---|
| Too short | The shift may not complete, leaving the car in the old gear. It can also land in a false neutral, after which the box drops into either the old or new gear. On a motorbike-style sequential, a 1st to 2nd shift may catch the real neutral |
| Too long | Shifts work, but the driver has to wait before the next one is allowed. That costs time on quick back-to-back shifts |
How we tune it
- Start on the long side so every shift completes.
- Log gear position alongside the shift outputs, and air pressure if you have it.
- Shorten the time in small steps, checking that each shift still completes cleanly in the log.
- Stop when you see the first sign of a missed or slow shift, then add a margin back.
- If the air is unregulated, repeat at low tank pressure before you call it done.
A missed shift under load is hard on a gearbox. When in doubt, a slightly longer duration is the safer choice.
Related settings: Shift Inhibit, RPM Shift, Flat Shift Link Delay and the wider Transmission Control function.
