A single sided power meter measures the output of one leg and infers total power based on the assumption that both legs contribute equally. This simplifies installation and bike swapping, but it relies on a mathematical estimate rather than a direct measurement of total work.
For most structured interval blocks, a consistent estimate is usually sufficient to track repeatable power numbers. However, dual sided measurement provides a different data set entirely by identifying leg imbalance. This distinction matters when the goal shifts from total physiological load to analyzing pedal stroke efficiency.
How should a buyer weigh the simpler installation of single-sided measurement against the assumptions involved in estimating total power?
For structured intervals, a repeatable number is exactly what you need. The math behind single-sided meters is good enough to keep targets consistent, and chasing absolute precision won’t make your FTP any higher.
Consistency matters, but you still need to know the error envelope of the meter you choose. A typical single‑sided unit will be within ~2% of true power when both legs are equal, so using it to set FTP and drive interval zones introduces negligible systematic drift. If you have a leg power imbalance of 10% or more, the inferred total can be off by a comparable amount, which will shift your zone targets. For pure repeatable interval work that’s calibrated to the same meter, that bias cancels out – consistency wins. When you want to analyze pedal stroke, compare across bikes, or use power for race pacing, the extra cost and installation effort of a dual‑sided sensor is justified. In short: pick single‑sided if you only need repeatable load for structured blocks; go dual‑sided if you need leg‑balance data or cross‑bike comparability.
