Why You Need a Power Meter and How to Choose One
Heart rate tells you how your body is reacting to effort — with a lag, and shaped by sleep, caffeine, and heat. Power tells you exactly what you're doing, in watts, right now. That's why the power meter became the most important tool in structured cycling training.
Why measure power
- Objective, instant effort measurement — a watt is a watt, regardless of wind, fatigue, or weather.
- Training in FTP-based zones instead of guessing by feel.
- Even pacing on climbs and time trials — you stop starting too hard.
- Tracking progress — comparing the same number month over month.
- Input for fitness models — training load, fatigue, freshness.
Where power meters mount — the types
| Location | Pros | Cons |
|---|---|---|
| Crank arm | Cheap, easy install, often single-sided | One-sided measurement (see below) |
| Spider | Accurate, measures both legs together | Pricier, tied to a specific crank mechanism |
| Pedals | Easy to swap between bikes, L/R measurement | Price, more exposed to impact |
| Hub | Drivetrain-independent | Tied to a specific wheel |
Single-sided or dual-sided — which do I need?
The cheapest meters (typically in the left crank arm) measure only one leg and double the result, assuming symmetry. In practice, most cyclists have some asymmetry, but for zone-based training, single-sided measurement is entirely sufficient — what matters is repeatability, not absolute watt-perfect truth. Dual-sided (L/R) measurement is worth it for technique analysis, rehab, or competitive riders chasing detail.
What to check before buying
- Compatibility — crank type, arm length, frame clearance for pedal-based systems.
- Connectivity — ANT+ and Bluetooth, so it works with your head unit and apps (including on the trainer).
- Accuracy — manufacturers typically quote ±1–2%; consistency over time matters more than the raw number.
- Power source — replaceable or rechargeable battery, and stated run time.
- Calibration (zero offset) — do it regularly; it's the key to trustworthy data.
How to get started
Measure your FTP (a 20-minute test × 0.95 is a common method) and set your power zones. Train within those zones: most of the time easy (aerobic base), part of it in hard intervals. Zero-offset before every ride and watch the trend, not individual seconds. Analyze your data after training to see how your fitness is actually progressing.
Bottom line: a power meter turns "training by feel" into training on numbers — it lets you pace evenly, train in zones, and measure real progress. A cheaper single-sided meter with ANT+/Bluetooth is entirely enough to start; what matters most is repeatability and regular calibration. Once you're collecting watts, analyze them alongside recovery — fitness builds after training, not during it.
Train smarter with WattLog.pro
WattLog.pro collects data from your trainer and shows what's really happening with your fitness.
Try WattLog.pro for free →