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Fuel calculator explained

The fuel calculator powers two surfaces:

  • The projection panel on every race plan (top of the plan detail page).
  • The standalone /tools/fuel page for one-off "how much fuel do I need" what-ifs. You can reach it from the Fuel Calculator link in the user menu (click your avatar in the top-right of any signed-in page).

Same math, different surfaces. This page explains what the math does and what each input means.

What the calc returns

Given race duration + average lap time + fuel per lap + tank capacity, the calc returns:

  • Total laps — duration / avg lap.
  • Laps per tank — tank / fuel per lap.
  • Total stops — ceil(laps / laps per tank) - 1.
  • Total pit time — stops × pit-loss seconds.
  • Binding constraint — which is the tighter limit: fuel or NRG.

The projection panel renders all five.

Dual-constraint cascade (fuel + NRG)

When you add NRG inputs (Hypercar, GT3, or LMP2 — see NRG and car class), the calc runs a second projection against NRG capacity and reports whichever is tighter.

  • Fuel-bound — laps per tank is lower than laps per NRG charge; fuel decides your stop cadence.
  • NRG-bound — laps per NRG charge is lower; NRG decides.
  • Balanced (either) — both arrive at the same lap count. Stop cadence is the same whichever runs out first.

The plan detail page shows a badge in the projection panel. If you see "NRG-bound" but you expected fuel-bound, your NRG burn is more aggressive than the tank allows — consider a less aggressive map or a save-mode strategy.

The NRG section of the new-plan form adapts to your team's sim — ACC teams don't see it at all, iRacing teams see Hypercar only, LMU teams see all three classes. The standalone Fuel Calculator (/tools/fuel) has no team context, so it offers all three regardless.

Pit-loss cascade

Pit loss feeds into total pit time. The calc picks the most precise input you've provided:

  1. Per-stop breakdown (preferred) — pit lane + with-tires + without-tires + 2-tires, applied per stint based on the pit_type set on each stint (4 Tires / 2 Tires / No Tires). Most accurate.
  2. Per-stop typical — pit lane + worst-case pit-stop (with-tires), applied across all stops. Assumes the slow stop every time.
  3. Legacy typical — single pit_loss_seconds value, applied across all stops. For plans built before the per-stop split landed.

If a stint has no pit_type set, the cascade falls back to the typical estimate. The projection panel labels which branch produced the number (from per-stop breakdown or typical estimate).

What the calc doesn't do

  • We don't read live telemetry. The math assumes consistent laps — same lap time, same fuel burn, same NRG burn — across the race. Real races vary (FCY, incidents, weather, traffic), so use the projection as a planning target, not a race-day forecast.
  • We don't account for full course yellows or safety car laps.
  • We don't simulate when to take stops relative to other strategies (pit-window optimization). The calc tells you how many stops, not when.

For NRG specifics, see NRG and car class.

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