What this is
A first-principles physics model of electric-vehicle road trips. From a vehicle's road-load coefficients, mass, usable battery energy, and measured DC charging curve, it computes range as a function of speed, charging time between any two states of charge, and the headline result: the maximum achievable average speed — the sweet spot between driving faster (more drag) and charging longer (diminishing charge rate).
Nothing is curve-fit to look right. Every number comes from published physics: aerodynamic drag, rolling resistance, drivetrain efficiency, and trapezoidal integration of measured charging curves. Validated against EPA label ranges across the vehicle fleet (combined-range agreement typically within ±4%) and against independent 70-mph road tests; the vehicle-by-vehicle comparison is on the vehicle summaries page. Estimates assume a steady speed at 68 °F, zero wind, near-sea-level air density, and a 650 W accessory load (climate control, the 12-volt system, lights). The EPA label validation runs at the test-cycle figure of 250 W with no climate control; set that under Trip conditions to reproduce it. Cold weather, HVAC, wind, and elevation change real-world results.
Why the charger detour is one number. The time to get off the road to a charger and back is paid at every stop, whether you charge a little or a lot there. So no single charger's detour changes when you should unplug; only the average detour over the trip does, because it sets how many stops the trip needs. With the same arrival percentage and the same charge curve at every stop, the best unplug point is the same at every stop. This was checked by brute force on random trips with detours from 3 to 15 minutes: charging to the average-detour optimum at every stop matched the best possible plan, and every stop-by-stop variation lost time. The model assumes a charger is available wherever you reach your arrival percentage; when the next charger you intend to use is farther than that, distance sets the floor, not the sweet spot.
Math model & calculations
Copyright © 2026 Feather Solar, LLC.
Licensed under the GNU General Public
License v3.0. This program is free software: you can redistribute it and/or modify it
under the terms of the GPL as published by the Free Software Foundation, either version 3
of the License, or (at your option) any later version. It is distributed in the hope that
it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
Charge curve data
Charging curve data is compiled from multiple public sources. The source of each
individual curve is credited in data/chargecurves.json and shown in the
charge-curve chart title. Curves credited to
@OutofSpecReviews come from
Out of Spec Studios' published charging tests. The BrightDrop 600 curve
(@lightpowered) is Power of Light's
own measured data.
How exact is a curve? Every curve here is one measured session on one car. Charge rate changes with battery temperature, state of health, how hard the pack was worked before the stop, the charger and its power limit, and the weather. Treat a curve as representative of that model, not as a specification. Your car will not match it point for point, and two runs in the same car on different days will not match each other either. The charging times on this site inherit that spread, so read them as a good estimate rather than a promise.
One curve is a special case. The 2027 Rivian R2 curve was traced by eye from a chart shown in an Out of Spec video rather than taken from a logged session, so it is rougher than the rest and its charging times run a little optimistic. It will be replaced if a measured R2 curve is published.
Privacy
This site sets no cookies, runs no analytics, shows no ads, and collects no personal information. Your theme and skin preferences are stored only in your own browser (localStorage) and never leave your device. The physics runs entirely in your browser; vehicle selections and custom inputs are not transmitted anywhere. Web fonts are loaded from Google Fonts, which involves your browser requesting font files from Google's servers. Links to YouTube are plain links, not embedded players.
US government data (public domain)
- EPA Test Car List Data (coast-down coefficients, test weights) — epa.gov
- DOE/EPA Fuel Economy Guide (label ranges, MPGe, adjustment factors) — fueleconomy.gov
- EPA Dynamometer Drive Schedules (UDDS, HWFET) — epa.gov
The 0.7 default label-adjustment factor follows 40 CFR § 600.210-12(d)(3); vehicle-specific factors are used where the EPA data provides them.