Compare any two tire setups -- see how much more work your compressor signs up for.
I have a... (optional, improves PSI accuracy)
Air volume model: tire is approximated as a hollow cylinder (outer cylinder at the overall tire diameter minus an inner cylinder at the wheel diameter), then multiplied by an empirical 0.60 shoulder-taper factor calibrated against published tire acoustic-cavity volumes. Absolute per-tire volume is good to roughly +/- 15%; the percentage delta between two similar tires is much more accurate because the systematic error cancels.
Air mass model: ideal-gas, isothermal compression. Real compression heats the air (so the compressor does slightly more work than the model predicts), but the air cools in the tire afterward, so the steady-state pressure still tracks the isothermal math. We treat tire internal volume as constant across the PSI range (real tires bulge ~1-2% at higher PSI -- ignored).
Compressor curves: MORRflate TenSix and FiveSix curves come from MORRflate's published delivered-CFM table. The "typical 12V baseline" curve represents the VIAIR 88P / Smittybilt 2781 / Slime Pro-Power class -- $70-130 pack-mounted units. Marketing claims 1.94-2.0 CFM free-air; real delivered output is closer to 1.5 CFM at 20 PSI and 1.0 CFM at 40 PSI. Duty cycle of 50% reflects published "30 min on / 30 min off" thermal ratings for a single air-up session; back-to-back sessions degrade further.
What the calculator is good for: the % work delta (how much MORE air your new setup needs) is the trustworthy hero number. The absolute minutes are within ~15-25% of real-world for 4-tire parallel air-up via a manifold.
Running...