Speed and Cadence Sensors: Placement, Types, and Installation

Where Do You Put a Speed and Cadence Sensor?

Speed and cadence sensors are typically placed on specific parts of your bicycle to accurately measure your pedaling revolutions per minute (cadence) and your wheel's rotational speed (which translates to ground speed), with placement varying based on whether you have separate or combined sensor units.

Understanding Speed and Cadence Sensors

Before delving into placement, it's crucial to understand the distinct functions of these two vital cycling metrics:

• Cadence Sensor: This device measures your pedaling rate, expressed in revolutions per minute (RPM). It detects the movement of your crank arm. A higher cadence often correlates with greater cardiovascular efficiency and reduced muscular fatigue, especially over longer durations.
• Speed Sensor: This sensor measures the rotation of your bicycle's wheel. By knowing the wheel's circumference, your cycling computer or app can accurately calculate your real-time speed and total distance covered. This is particularly useful when GPS signals are weak, inconsistent, or unavailable, such as indoors or in dense urban areas.

Together, these sensors provide critical data for monitoring performance, optimizing training, and achieving specific physiological adaptations.

Sensor Types and Their Placement

The exact placement of your speed and cadence sensors largely depends on the type of sensor unit you possess:

Separate Speed and Cadence Sensors

Many manufacturers offer individual sensors, each optimized for its specific measurement.

• Cadence Sensor Placement:
  • Crank Arm: The most common and recommended placement for a standalone cadence sensor is on the inside of the non-drive side crank arm. It should be positioned securely with zip ties or strong rubber bands, ensuring it doesn't interfere with your shoe or the frame during pedaling. Some designs may use adhesive.
  • Pedal Spindle (less common standalone): Certain specialized cadence sensors integrate directly into the pedal spindle, offering a very clean aesthetic, but these are less common as standalone units.
• Speed Sensor Placement:
  • Wheel Hub: Modern speed sensors often attach directly to the hub of either the front or rear wheel. This provides a clean, unobtrusive installation and is generally less prone to interference than older magnet-based systems. It uses accelerometers or gyroscopes to detect rotation.
  • Wheel Spoke/Chainstay (older or simpler designs): Traditional speed sensors required a magnet attached to a spoke and the sensor unit mounted on the fork (for front wheel) or chainstay (for rear wheel). The sensor detects each pass of the magnet.

2-in-1 Combo Sensors

Some manufacturers offer a single unit that performs both speed and cadence measurement. These are typically mounted in a specific location that allows them to detect both types of movement.

• Chainstay Mounting: The most prevalent design for combo sensors involves mounting the unit on the non-drive side chainstay. These sensors usually have an internal accelerometer that detects the movement of the chainstay relative to the crank arm for cadence and the wheel for speed. Proper orientation, often indicated by an arrow on the sensor pointing towards the front of the bike, is crucial for accurate readings.
• Magnet-Based Combo Sensors: Older combo sensors, or some entry-level models, still rely on magnets. These require a magnet on a spoke for speed and a magnet on the crank arm for cadence. The single sensor unit is then strategically mounted on the non-drive side chainstay so it can detect both magnets as they pass.

Detailed Placement Instructions for Optimal Performance

Regardless of the sensor type, precise installation is key for accurate data acquisition.

• Cadence Sensor (Crank Arm):
  • Location: Position the sensor on the flat, inside surface of the non-drive side crank arm.
  • Security: Use the provided rubber bands, zip ties, or adhesive to fasten it firmly. It should not wiggle or shift during pedaling.
  • Clearance: Ensure there's ample space between the sensor, your shoe, and the bicycle frame. Pedal through a full revolution to check for any contact.
  • Orientation: Some sensors have a specific orientation for optimal data collection (e.g., an arrow pointing towards the pedal). Follow the manufacturer's instructions.
• Speed Sensor (Wheel Hub):
  • Location: Attach the sensor securely to the hub of either the front or rear wheel. The rear wheel is often preferred if you're only using one, as it's less exposed to road debris.
  • Security: Use the provided rubber band or mounting mechanism to ensure it's centered and tight on the hub.
  • Orientation: Many hub-based speed sensors are omnidirectional, but some might have an optimal alignment. Check the manual.
  • Wheel Size Calibration: After installation, it's critical to input your exact wheel circumference into your cycling computer or app. This can usually be found on your tire sidewall (e.g., 700x25c) and converted to millimeters, or you can measure it precisely.
• Combo Sensor (Chainstay):
  • Location: Mount the sensor on the non-drive side chainstay, typically closer to the crank arm/bottom bracket area.
  • Security: Use the provided rubber bands or zip ties to secure it firmly.
  • Orientation (Accelerometer-based): Ensure the sensor is oriented according to the manufacturer's instructions, often with an arrow pointing forward. This allows it to correctly differentiate between crank and wheel movements.
  • Magnet Alignment (Magnet-based Combo): If using a magnet-based combo sensor, ensure the crank magnet passes directly over the cadence detection area of the sensor, and the spoke magnet passes directly over the speed detection area. Adjust the sensor's position on the chainstay and the magnets' positions as needed to achieve a gap of 1-5mm.

Key Considerations for Installation

• Compatibility: Ensure your sensors are compatible with your cycling computer, smartwatch, or smartphone app (e.g., ANT+, Bluetooth Smart).
• Security: A loose sensor can provide inaccurate data, get damaged, or even fall off during a ride. Double-check all fastenings.
• Clearance: Always ensure that no part of the sensor or its mounting interferes with your bike's moving parts (crank, wheel, spokes, chain) or your body (shoes, ankles).
• Battery Access: Consider future battery changes during installation. Try not to obscure the battery compartment if possible.
• Weather Protection: Most modern sensors are weather-resistant, but ensure they are not exposed to direct, sustained water spray if avoidable, and clean them periodically.
• Calibration: For speed sensors, accurate wheel circumference input is paramount for precise speed and distance readings.

Testing and Troubleshooting

Once installed, perform a quick test to ensure proper function:

1. Pairing: Connect your sensors to your cycling computer or app.
2. Spin Test:
   • Cadence: Rotate the cranks a few times by hand or pedal gently. Your device should display a cadence reading.
   • Speed: Lift the rear wheel and spin it. Your device should show a speed reading.
3. Common Issues:
   • No Reading: Check battery, ensure sensor is "awake" (some require movement), re-pair the sensor, or check for correct orientation/magnet alignment.
   • Inconsistent Reading: Ensure sensor is tightly secured and clear of interference.
   • Incorrect Speed: Double-check your wheel circumference setting in your device.

The Benefits of Accurate Data

Properly installed and calibrated speed and cadence sensors unlock a wealth of training benefits:

• Performance Tracking: Precisely monitor your efforts, track personal bests, and measure progress over time.
• Training Zones: Maintain specific cadence or speed targets to train effectively within different energy systems or for specific goals (e.g., high cadence for endurance, higher speed for intervals).
• Efficiency: Analyze your cadence to optimize your pedaling technique, aiming for a smooth, consistent stroke that conserves energy.
• Pacing: Use real-time data to maintain your desired effort level during races, long rides, or structured workouts, preventing premature fatigue.

By understanding the mechanics and following these detailed placement guidelines, you can ensure your speed and cadence sensors provide the accurate, reliable data essential for informed training and enhanced cycling performance.