The W-tau test protocol: how we measure your two recovery times
You can't improve what you don't measure. Your recovery time — your W-tau — isn't a number an app makes up for you, but something measured on you. Here's how: three ramps, two recovery points, one clear profile.
Rob Bohte, physician and coach · updated
Recovery isn't one rate but two: a fast phase of tens of seconds and a slow one of minutes (each with its own time constant τ). To capture both, we measure not once but twice — after a short pause and after a longer one. The difference between those two measurements fixes your fast and your slow recovery time.
The idea: empty the battery, then see what comes back
You don't measure your W-tau at rest — you measure it by first genuinely emptying your attack battery (W′), then seeing how much comes back after a short and a longer recovery pause. A lot back after 30 seconds = a fast first phase. Only a lot back after a few minutes = a slow second phase.
We don't ride an all-out sprint but a ramp: power rises steadily (around 20 watts per minute) until you can't continue. A ramp is far easier to ride to true exhaustion without a supervisor than a sprint — you don't collapse partway and you don't mistime it.
Three ramps, two recovery points
From the two measurements we compute your fast and slow recovery time (τ) — together your W-tau. Your CP and W′ from the CP test stay the anchor beneath it.
Why exactly 30 and 240 seconds
One measurement point can't separate the two phases. After 30 seconds mainly your fast phase is active; after 240 seconds your slow phase has had time to refill. By measuring at exactly those two moments, we can estimate the fast and the slow recovery time separately — not an average, but two numbers that together form your recovery profile.
The proof that you were really empty
A recovery time only means something if the exhaustion ramp truly drained your battery. That's why at every stop we also record your cadence and your RPE (how hard it felt): if you could still pedal smoothly at the end, it wasn't maximal and the measurement is off. If you stall with cadence dropping away, we know W′ was genuinely empty — and only then does the recovery after it mean anything.
Common mistakes
- ✗Riding the exhaustion ramp too cautiously — then your battery isn't empty and you measure recovery that wasn't there.
- ✗Not riding the recovery pauses at the agreed recovery power: too hard = you don't recharge, too easy = you measure something else.
- ✗Shortening or stretching the pauses: 30 and 240 seconds are the measurement points; deviate and the taus are off.
- ✗Testing on a day you're tired or not rested — recovery is temporarily slower then and not representative.
- ✗Using a different CP/W′ underneath than your current one: recovery is measured against your limit, so that has to be right.
Start with the basics
Your W-tau builds on your CP and W′. Start with the CP test (€ 9.90) — then we have the anchor, and measure your personal recovery times from there.