# Calculating power output on a spin bike

• I
• SpinnerDude
In summary, the conversation discusses using a home spin bike without sensors to calculate power output. The bike has an 18kg flywheel, direct drive, and a magnet for resistance. The idea is to map the resistance settings and calculate power output based on cadence alone. Further considerations include calculating the Moment of Inertia and removing the magnet temporarily to measure spin down time without damping.

#### SpinnerDude

So...I have a home spin bike which unfortunately lacks the sensors of some of the more expensive models. What I'm trying to do is work out if I can dynamically calculate my power output.

The spin bike itself has:
- An 18kg flywheel of radius 30cm
- Direct drive between the crank and the flywheel (one turn of the crank = six turns of the flywheel)
- Resistance is provided by a magnet that is lowered onto the flywheel rim
- An additional cadence sensor on one of the crank arms

It feels like I should be able to map the resistance settings on the bike, such that the power output can be calculated based on the cadence alone.

My first thoughts are around pedalling at a set cadence and seeing how long the flywheel takes to stop, and from there working out the resistance produced by the magnets (which I'm currently assuming to have a linear relationship with the angular velocity of the flywheel)

SpinnerDude said:
My first thoughts are around pedalling at a set cadence and seeing how long the flywheel takes to stop, and from there working out the resistance produced by the magnets (which I'm currently assuming to have a linear relationship with the angular velocity of the flywheel)
That sounds like a good plan to me. You will need to accurately calculate the Moment of Inertia of the flywheel (is it a perfect disk shape, or does it have a flange like lifting weights?), and you should remove the magnet temporarily so you can see how long it takes to spin down with no explicit damping/drag (to be able to separate the friction terms of the damping).

## 1. How do I calculate power output on a spin bike?

To calculate power output on a spin bike, you will need to know the resistance level, cadence (RPM), and duration of your ride. The formula for calculating power output is: Power (watts) = (2.8 x resistance level x cadence) / 60. This will give you the average power output for your ride.

## 2. Is power output the same as wattage?

Yes, power output and wattage are essentially the same thing. Power output is the amount of energy being produced per unit of time, and it is measured in watts.

## 3. How accurate is the power output measurement on a spin bike?

The accuracy of the power output measurement on a spin bike can vary depending on the quality and calibration of the bike's power meter. However, most spin bikes use a strain gauge to measure power, which is a highly accurate method.

## 4. Can I use power output to track my fitness progress?

Yes, power output is a great way to track your fitness progress on a spin bike. By consistently monitoring your power output, you can see improvements in your strength and endurance over time.

## 5. How does power output affect my calorie burn?

Power output is directly related to calorie burn on a spin bike. The higher your power output, the more energy (calories) you are expending during your ride. This can be a helpful metric for those looking to track their calorie burn and weight loss goals.

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