Swim economy calculator (VO₂max → swim time), Yousuli Help

What it does

The swim economy calculator projects a swim leg time from your VO₂max, cost of swimming (Cr), the share of VO₂max you can sustain for the duration, and environmental modifiers (open water type, drafting, chop, sighting). It also outputs pace per 100 m, pace per 100 yd, VO₂ at the predicted pace, the effective Cr after modifiers, and an optional faster/slower uncertainty band.

URL: /calculators/ then open Swim economy. Direct path: /static/calculators/swim_economy_calculator.html.

Inputs the form asks for

Distance

Distance preset (select) — common race distances.
Custom distance (m) — used when the preset is set to Custom.

Physiology

VO₂max (mL/kg/min).
Mass (kg).
Cr tier (select) — economy tier with a default Cr value per tier. Labels match the form verbatim ("Well-trained (Cr 0.70)", "Trained (Cr 0.78)", etc.). Pick the tier and the Cr override below auto-fills.
Cr override (numeric) — bypass the tier default with a measured Cr from a lab test or the calibration block (see below).
Fraction of VO₂max (%) — share of VO₂max you can hold for the projected duration.

Conditions

Environment (select) — Pool 25 m / Pool 50 m / Open water calm / Open water rough / etc. Each adds a small efficiency or drag multiplier.
Draft (select) — None / Behind one swimmer / In a pack. Drafting reduces effective Cr by a known fraction.
Chop (select) — Calm / Light / Moderate / Heavy. Increases Cr at higher levels.
Sighting frequency (select) — controls the sighting penalty for open-water swims. More sighting = more Cr.

Model toggles

VO₂ kinetics toggle (checkbox) — when on, applies an on-kinetics correction to the first ~τ seconds (default Tau ≈ 25 s). Matters more for shorter swims where the warm-up phase is a meaningful share of total time.
Tau (s) — time constant for the kinetics correction.
Show band (checkbox) — toggles the faster/slower uncertainty band on the predicted time.

Cr calibration block

If you have a known historical swim result, this block lets you back-solve a personalised Cr:

Known Distance (m).
Known Time (min:sec split into two fields).
Outputs an Implied Cr that you can copy into the Cr override above for future projections.

Outputs

Predicted Time (mm:ss).
Pace per 100 m.
Pace per 100 yd.
VO₂ at predicted pace (mL/kg/min).
Effective Cr — the Cr after environment / draft / chop / sighting modifiers are folded in.
Faster / Slower band — ±10% Cr range expressed as faster and slower projected times (when the Show Band toggle is on).

When to use it

Race-day swim time projection when you have a VO₂max estimate but not a recent CSS test.
Comparing two race-day scenarios (pool vs choppy open water, draft vs no draft) at a time-projection level.
Sanity-check against a CSS -derived pace projection — different model, useful cross-check.

When NOT to use it

If you have a recent CSS test, the CSS calculator is a more direct anchor for sustained swim pace.
For pool sets / interval prescriptions — those use CSS, not this VO₂max-based projection.

Swim economy calculator (VO₂max → swim time)