How to Install Electric Bike Pedal Assist Sensor

Installing a pedal assist sensor (PAS) on your electric bike is a great way to enhance your riding experience, as it allows the motor to engage based on your pedaling effort. 

Whether you're upgrading your bike or replacing a malfunctioning sensor, proper installation is key to ensuring your PAS system works smoothly.

This guide will walk you through the detailed steps required to successfully install a PAS and get your bike ready for action.

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What You Will Need

Before diving into the installation, make sure you have all the necessary tools and parts to complete the job. Here’s a list of what you’ll need:

• Pedal assist sensor (PAS) kit: Includes the sensor and magnetic disc.

• Allen wrenches: For loosening and tightening bolts.

• Crank puller: If needed to remove the crank arm.

• Screwdriver: A small Phillips or flathead screwdriver for securing the sensor.

• Zip ties or cable clips: To tidy up and secure the sensor cable.

• Cleaning cloth: To ensure a clean installation surface.

Having these tools ready will help ensure a smooth and efficient installation process.

Step 1: Remove the Bike Crank Arm

Before you can install the PAS, you will need to remove the crank arm from your bike. Follow these steps to remove it safely:

1. Loosen the crank arm bolt: Use the appropriate-sized Allen wrench to loosen the bolt on the crank arm. Depending on your bike, the bolt may be on the left or right side.

2. Remove the crank arm: If the crank arm does not come off easily, use a crank puller to help. The crank puller will allow you to remove the crank arm without damaging any components.

3. Set aside the crank arm: Once the crank arm is removed, set it aside safely. You'll need to reinstall it after installing the sensor.

Removing the crank arm gives you access to the bottom bracket, where the magnetic disc and sensor will be installed.

SEE ALSO Solutions for Ebike PAS Always Going Full Speed

Step 2: Install the Magnetic Disc

The magnetic disc is essential to the pedal assist system, as it rotates with the crank, allowing the sensor to detect your pedaling effort. Follow these detailed steps to install it correctly:

Positioning the Magnetic Disc

Check the bottom bracket area where the pedal cranks attach to the bike frame. This is where you will place the magnetic disc on the spindle (the axle that runs through the bottom bracket).

If you have a split magnetic disc (common in most PAS kits), open it and clip it around the spindle. Ensure the magnets face outward, toward where the sensor will be mounted. This type of disc is convenient, as you don’t have to remove the entire bottom bracket to install it.

If your magnetic disc is solid (not split), you’ll need to slide it onto the spindle. This may require additional steps like removing the crankset to access the spindle, depending on your bike type.

Securing the Magnetic Disc

After positioning the disc, ensure it rotates freely when you turn the pedals. It should fit snugly around the spindle but move without any resistance.

Some discs are secured with small screws or retaining clips. If yours has this feature, carefully tighten the screw to keep the disc in place. Make sure not to overtighten, as this can damage the disc or prevent smooth rotation.

If your disc does not have screws, the tension between the spindle and crank arm will keep it secure. Be sure to double-check that the disc is stable before moving to the next step.

Test Fit

Spin the pedals to ensure that the magnetic disc moves freely and does not wobble.

Ensure the magnets are positioned to pass close to the sensor once it is installed. Proper alignment here is crucial for the system’s functionality.

The magnetic disc needs to be securely installed to provide accurate signals to the sensor, ensuring the motor engages when you pedal.

Step 3: Mount the Pedal Assist Sensor

Once the magnetic disc is in place, it’s time to mount the pedal assist sensor. This sensor detects the rotation of the magnetic disc and sends signals to the motor controller. Follow these detailed steps to mount the sensor properly:

Choose the Sensor Mounting Spot

The sensor is usually mounted on the non-drive side (the side without the chain) of the bike frame, typically near the bottom bracket or along the chainstay. This allows it to be positioned close to the magnetic disc.

Ensure that the sensor cable can be routed easily to the bike’s controller or wiring harness. Make sure there is enough slack so that the cable won’t be strained during turns or pedaling.

Mounting the Sensor

Most sensors come with either a clamp-style bracket or adhesive backing. If using a clamp-style bracket, attach the sensor securely to the frame, positioning it so that the magnetic disc will pass by the sensor with about 1-3 mm of clearance. Tighten the clamp firmly to prevent movement.

If using an adhesive-backed sensor, clean the frame with a cloth to remove any dirt or grease. This will ensure a strong bond. Stick the sensor firmly to the cleaned surface, again ensuring the correct distance between the sensor and magnetic disc.

Align the sensor so that the magnets on the disc pass directly in front of it during each pedal rotation.

Align the Sensor and Magnetic Disc

With the sensor mounted, spin the pedals and observe the alignment between the sensor and the magnetic disc.

The magnets should pass close to the sensor, with no more than 3 mm of clearance.

If the gap is too large or the disc rubs against the sensor, adjust the sensor position accordingly.

Secure the Sensor Wire

Run the sensor cable along the bike frame, using zip ties or cable clips to keep it tidy and prevent it from getting caught in any moving parts.

Ensure there is enough slack in the wire to accommodate the movement of the bike, but not so much that it dangles loosely.

Leave some slack near the sensor itself to account for vibrations or minor frame flex during rides.

Final Alignment and Test

After securing the wire, spin the pedals again to ensure that the sensor is reading the magnetic disc properly.

Power on your bike and select a low pedal assist level to test whether the motor engages as expected when you turn the pedals.

Proper alignment and secure mounting of the sensor are crucial to the overall performance of your electric bike’s pedal assist system.

Step 4: Reinstall the Crank Arm

Once the magnetic disc and sensor are correctly installed, you can now reinstall the crank arm:

Position the Crank Arm:

• Align the crank arm with the spindle, ensuring it sits at a 180-degree angle from the opposite crank arm for balanced pedaling.

Tighten the Crank Arm Bolt:

• Using the same Allen wrench, securely tighten the crank arm bolt. Ensure there’s no looseness or play in the crank arm, as this could cause damage or create unsafe riding conditions.

Test Pedal Rotation:

• Spin the pedals to check that they rotate freely and the magnetic disc passes smoothly by the sensor.

Step 5: Test the Pedal Assist System

• Power on the bike: Turn on your electric bike’s power and select a pedal assist mode from the display.

• Spin the pedals: Lift the rear wheel off the ground and manually spin the pedals. The motor should engage after a few pedal rotations.

• Adjust if Necessary: If the motor does not activate or behaves erratically, check the alignment between the sensor and the magnetic disc. Make any necessary adjustments to improve performance.

• Test Ride: Take the bike for a short test ride, confirming that the pedal assist system works smoothly and delivers the right level of power based on your pedaling effort.

Conclusion

Installing a pedal assist sensor can seem like a daunting task, but with the right tools and careful attention to detail, you can complete the installation successfully. 

FAQs

What is a pedal assist sensor (PAS)?

A pedal assist sensor (PAS) is a component in an electric bike that detects when and how much you are pedaling. It signals the bike’s motor to provide assistance based on your pedal effort, making the ride easier, especially on hills or during long distances.

How does a pedal assist sensor work?

The PAS works by using a magnetic disc and a sensor. As you pedal, the magnets on the disc pass by the sensor, which sends signals to the bike's controller. Based on the sensor's data, the motor engages to provide assistance in proportion to how fast you're pedaling.

Do all electric bikes have pedal assist sensors?

Not all electric bikes come with pedal assist sensors. Some models rely solely on a throttle, while others have a combination of both throttle and PAS. If your bike doesn’t have a PAS, you can often install one to enhance your riding experience.