What shock travel sensors tell you
A shock travel sensor is a linear position sensor mounted alongside the shock absorber. As the suspension compresses and extends, the sensor's shaft moves with it and its output voltage changes. Logged at speed, that gives you a trace of every movement the wheel makes. It's sensitive enough to pick up tire shake and small oscillations, not just big bumps.
That's why drag racers and road-race teams rely on them. You can see how far the rear squats on launch, whether the front is lifting, how fast the car settles, and whether a change to shocks, springs or tire pressure actually helped. Because the Elite logs suspension alongside RPM, boost, wheel speed and throttle, you can line up a tire shake event with exactly what the engine was doing at that moment.
Haltech's linear position sensors come in several stroke lengths. Mounting hardware includes the weld-on tab and split-collar clamps like the 1" split collar mount. Choose a stroke a little longer than the shock's full travel so the sensor can never bottom out before the shock does.
Wiring and input choice
Each sensor needs an input on the ECU, so four corners means four inputs. On the Wiring tab, pick the input for the shock travel channel:
- AVI (analog voltage input): the preferred choice. These inputs are built for varying voltages like this one.
- SPI (synchronized pulsed input): works when the AVIs are all used. Set the Sensor Type to Hall Effect, which is the correct setting whenever an SPI reads an analog signal.
Should the pullup be on?
The AVI pullup adds a 1k resistor to 5V, and the SPI pullup adds a weaker 10k one. Pullups exist for sensors that don't make their own voltage, such as two-wire temperature sensors. A linear position sensor is normally powered from the ECU's 5V supply and drives its own output, so in most installs the pullup should be disabled. Leaving it on pulls the signal toward 5V and distorts the reading. The same applies if a sensor is shared with another controller that already provides one.
Calibration
The Calibration tab turns the sensor's voltage into a travel reading. ESP ships with a number of calibrations. Load one with the Open icon, or build your own from the manufacturer's data and keep it with the Save icon.
We like to check the calibration on the car. With the car at ride height, note the reading. Then compress and extend the corner (springs off, or with a jack) and confirm the change in reading matches a tape measure. A zero point at ride height makes the logs much easier to read, because compression and extension show up as positive and negative movement.
Mount the sensor so it moves in a straight line with the shock. Any side load on the shaft will wear it quickly and put noise in the signal. Route the cable with enough slack for full droop and full bump.
Display range
Display Minimum and Display Maximum set the scale of shock gauges in ESP. They change only what's drawn on screen, not what the ECU measures or logs. Set them to just beyond the travel you expect, so the needle uses the whole gauge without clipping.
Diagnostics
The Diagnostics tab lets the ECU flag a failed sensor or damaged wiring. Both checks are off by default.
| Setting | Code | Catches | Our advice |
|---|---|---|---|
| Raw Min | C0615 | Signal voltage below your limit, typically a short or broken supply | Set it below the lowest voltage at full extension |
| Raw Max | C1760 | Signal voltage above your limit, typically a short to 5V or a wiring fault | Set it above the highest voltage at full compression |
If Engine Protection is active, you can give either fault a DTC Severity. For a data-only sensor, a low severity that logs the fault is usually enough.
Troubleshooting
| Symptom | Usually |
|---|---|
| Reading pinned near 5V | Pullup left on, or the signal wire shorted to 5V |
| Reading pinned near 0V | No 5V supply to the sensor, or a broken signal wire |
| Travel scale is wrong | Wrong calibration for the sensor's stroke |
| Noisy trace at rest | Side-loaded shaft, loose mount or a poor ground |
FAQ
What's the difference between shock travel and ride height sensors?
Shock travel measures movement at the damper. Ride height sensors measure the distance from the chassis to the ground. Many racers run both, and ride height is also useful for wheelie control.
Do I need all four corners?
No. On a drag car, the rear two often tell you most of what you need. On a road-race car, all four show roll and pitch.
