speed sensor mounting point confusion?

The speed sensor won't give you correct results on a flywheel of an indoor bike, no matter how you attach it. This is because the flywheel's rotation speed is not directly related to speed indicated by the bike.

I don't understand, can you explain in more detail? There are people on YouTube and Amazon who installed it on a flywheel and were happy with the results. Are you absolutely sure that what you say is true?

https://youtu.be/F6Cv0bL3M98?si=dXtAdzTzfaYnN2op

https://youtu.be/IL6iNchR-Mo?si=TUJMf482vNJtDmY0

That depends on how you define "happy with the results".

The speed sensor does not provide speed. It provides wheel revolutions per minute. This data is then used by the watch to calculate speed based on wheel size. The thing is that an indoor bike doesn't have a real wheel, so you don't know how much distance should be added with each flywheel revolution. You could try guessing a wheelsize value, just as it is shown in the videos, but this would be just a random speed that YOU decided to be correct, and anyway this won't work for bikes, that provide different speeds for different resistance values.

I do not agree with you that you answered with technical information on this subject and from the answers you gave, I see that you do not understand the working principle of the speed sensor and what I mean. You are just trying to make people accept your own idea.

Formulas:

• Rotational Speed (dH):
  Rotational Speed (dH) = Number of Turns (n) / Time (t)
• Diameter (d):
  Diameter (d) = 2π * Radius (r)
• Radius (r):
  Radius (r) = Half the Distance (m)
• Distance Traveled (m):
  Distance Traveled (m) = Arc Length (s) = π * d * (n / t)

Application:

1. Obtain the Number of Turns (n) value by the sensor detecting the disk's rotation.
2. Measure the Time (t).
3. Calculate Rotational Speed (dH), Diameter (d), and Distance Traveled (m) using the above formulas.

Example:

• Number of Turns (n): 10
• Time (t): 10 seconds
• Diameter (d): 40 cm = 0.4 m

Calculations:

• Rotational Speed (dH): 10 turns / 10 seconds = 1 turn/second
• Radius (r): 0.4 m / 2 = 0.2 m
• Distance Traveled (m): π * 0.4 m * (1 turn/second * 10 seconds) = 4π m ≈ 12.57 m

Garmin Speed Sensor:

The Garmin Speed sensor detects the disk's rotation gyroscopically and uses this information to find the center of the disk and calculate the distance traveled. The sensor's operation is based on the formulas presented above. Attaching the sensor to the wheel's axle allows it to accurately determine the disk's radius.

Note: These calculations are made in an ideal environment. In reality, there may be slight differences in the distance traveled due to friction and other factors.

Additional Information:

• Angular Speed (ω): ω = 2π * dH
• Centripetal Acceleration (ac): ac = ω^2 * r

5949109 said:

The Garmin Speed sensor detects the disk's rotation gyroscopically

Well, not gyroscopically, but that's irrelevant.

5949109 said:

uses this information to find the center of the disk

It does not.

5949109 said:

Attaching the sensor to the wheel's axle allows it to accurately determine the disk's radius.

It does not. The sensor itself doesn't know anything about the wheel. It only knows how fast it rotates. Wheel size is set on the watch, and can be determined in two ways:

automatically (needs GPS, won't work for indoor bikes)

manually (as shown in your videos)