If you plan to use an indoor cycling app like Zwift, ROUVY, TrainerRoad, etc., you can use them without a power meter.
The apps will estimate your power based on a cadence and a speed sensor (assuming you don’t use them with a smart trainer). Unfortunately, your power data won’t be very accurate.
This is because:
The main difference between a power meter and a cadence sensor is that a power meter is more accurate in calculating your power than estimating it using a cadence sensor and the trainer’s power curve. It measures your force (torque) using strain gauges and angular velocity (cadence) that are needed for the calculation of power P=W/t.
Does an upgrade from a cadence sensor to a power meter pays off?
The short answer is yes. It does. But… (there is always but, right?), it depends on your goals.
Continue reading to find out more.
How Do Indoor Cycling Apps Get Your Power Data?
There are three options for indoor cycling apps to get your power data:
- Estimate it using your speed and/or cadence sensor.
- Receive it from a smart trainer.
- Receive it from your power meter.
1. Cadence and/or Speed Sensor
This is the most basic option how to use indoor cycling apps without a smart trainer or a power meter.
If you have a budget bike trainer that can’t measure your power, you need a speed or/and cadence sensor so that the app can estimate it. For example:
- Zwift estimates your power based on your speed and a trainer’s power curve. This feature is called zPower. (Source)
- The same applies to ROUVY, but they don’t have naming for it. (Source)
- TrainerRoad calls this feature VirtualPower. (Source)
The advantage of this method is that you don’t need a power meter or a smart trainer. However, it is not very accurate and usable for structured training.
2. Smart Trainer
Smart bike trainers can measure and transmit your power. There are two types of smart trainers:
- Interactive smart trainers can transmit your power data via ANT+ or Bluetooth and can be controlled via apps to adjust the resistance.
- Non-interactive smart trainers can only transmit your power data.
You can learn more in this article.
Indoor training with an interactive smart trainer brings the best possible riding experience. It makes you more engaged because you have to change gears when the terrain changes. Furthermore, you can take advantage of features like ERG mode.
The downside is obvious – you have to buy a smart trainer, which is far more expensive than the cadence and speed sensors.
3. Power Meter
The last option for how apps can get your power data is by getting it directly from a power meter.
Today’s power meters support ANT+ and Bluetooth protocols for transferring the (power) data. Read my how power meters work article to learn how they get your power.
Keep in mind that single-sided power meters estimate the power output of the right leg because they can only measure the actual power of your left leg. This means that the power meter will transmit zero power when pedaling with your right leg during single-leg drills.
The following table shows the pros & cons of using a power meter vs. cadence and speed sensor.
|Power Meters||• Provide more accurate data (power and cadence) to you and indoor cycling apps||• Are more expensive
• Single-sided power meters show zero power and cadence when pedaling with right leg
|Cadence and Speed Sensors||• Are more affordable||• Estimated power in indoor cycling apps is less accurate|
You may have noticed that I didn’t talk about cadence sensors much. So…
What Are Cadence Sensors Good for?
Cadence sensors provide you with information about how fast your legs are spinning.
Knowing your cadence is useful for structured training. For example, some intervals are low-cadence, some high-cadence, etc.
Can power meters measure your cadence?
Yes, power meters can measure your cadence. This means you don’t have to buy the cadence sensor if you buy a power meter.
How Accurate Are Indoor Cycling Apps in Estimating Your Power?
Depending on the cycling app, the power estimation based on a speed sensor and bike trainer varies.
Apps algorithms use the so-called power curves of bike trainers. For example, some trainers use linear (magnetic trainers) and some progressive resistance (wind and fluid trainers).
The following picture illustrates these power curves.
Zwift Insider found out that the Zwift’s zPower is surprisingly accurate given the fact it uses only your speed and trainers’ power curve.
Developers try to improve the accuracy with software updates. However, there is only so much they can do. Power meters and smart trainers will always be more precise.
This being said, if you are serious about your bike training, a power meter is a must.
Power Meters vs. Cadence and Speed Sensor FAQ
If you currently use a classic ‘dumb’ trainer and are serious about your training, buy a power meter to get more accurate power data. The power estimations based on your speed and cadence won’t be as accurate.
Additionally, if you plan to cycle indoors more often, consider buying a smart trainer. It helps you to get the most out of your indoor training thanks to its features like ERG mode, road-like-feel, etc.
Remember, you don’t have to buy all devices at once. For example, you can use a power meter and a dumb trainer during one or two seasons and upgrade to a smart bike trainer later.