How we work out real range & cost
Every range, cost and journey figure on HonestRange is computed by one physics model from each car's measured parameters — not WLTP, not a flat percentage. This page shows the equations, the constants and their sources, the current validation status, and who stands behind the model.
Validation status
The power model is designed to be validated against a BEV powertrain researcher's reference simulation at 30/50/70 mph and −5/10/20 °C, with our test suite failing if the error exceeds 5%.
Current status: the reference dataset is not yet in place. Our fixture tests presently run against provisional values generated by the model itself, which confirm internal consistency but do not yet confirm accuracy against an independent reference.
Because of that, we quote no validation-error figure here yet. When the reference data is in place, this section will show the actual error our tests produce — whatever it is. We would rather say "not yet validated" than imply a precision we haven't earned.
The model author's ORCID profile will be linked here for independent verification once the validation dataset is in place.
The equations
Power to move the car at a steady speed is the sum of four road loads plus cabin and auxiliary electrical draw. Speed v is in metres per second.
P_aero = ½ · ρ(T) · Cd · A · v³
P_roll = Crr · m_total · g · v (× 1.1 in rain)
P_drivetrain = (P_aero + P_roll) · (1/η_dt − 1)
P_hvac = heat-pump vs PTC model (below); P_aux = constant base load
efficiency (mi/kWh) = v_mph / (P_total / 1000)
Air density comes from the ideal gas law, so cold air (denser) costs more range. Cabin heating uses a resistive (PTC) demand of clamp((16 − T) · 180, 0, 4000) watts; a heat pump does the same job for 45% of that above -5 °C.
Battery degradation
State of health follows an exponential approach to a floor: SoH = floor + (1 − floor) · exp(−k · age), with k fitted so the first-year loss matches the calibrated annual figure for that chemistry and cooling type. Age and mileage are blended 70/30.
Journeys & cost
Journeys integrate energy leg by leg; a rapid charge (20→80%, approximated at 75% of the car's peak DC rate) is inserted before any leg that would fall below 10%. Running cost is energy + VED + (from the 2028/29 tax year) a 3p/mile charge, compared against petrol at a default 40 mpg.
Constants & sources
Every constant in the model carries a source. Items marked provisional are modelling assumptions or pending expert review and are not presented as measured fact.
| Constant | Value | Source |
|---|---|---|
| Gravity g | 9.80665 m/s² | CODATA / ISO 80000 standard value |
| Sea-level pressure | 101325 Pa | ISO 2533 Standard Atmosphere |
| Specific gas constant, dry air | 287.05 J/(kg·K) | CIPM-2007 dry-air molar mass |
| Rain rolling multiplier | × 1.1 | Wet-road Crr uplift — provisional, pending review |
| PTC heater ramp | 180 W/°C, cap 4000 W | Modelling assumption — provisional, pending HVAC dyno data |
| Base auxiliary load | 320 W | Modelling assumption — provisional |
| Heat-pump fraction of PTC | 45% above -5°C | Modelling assumption — provisional |
| Degradation age/mileage blend | 70 / 30 | Modelling assumption — provisional |
| Reference annual mileage | 8000 mi/yr | DfT National Travel Survey (rounded) — provisional |
| Journey SoC floor | 10% | Model rule (SPEC §5.3) |
| DC-curve de-rate | × 0.75 | Flat approximation of the DC taper — provisional |
| 2028/29 eVED | 3p/mile | Announced per-mile charge for EVs (indicative) |
| EV standard VED | £195/yr | VED reform from 1 April 2025 — refresh each tax year |
| Litres per UK gallon | 4.54609 | UK Weights & Measures Act |
Degradation & tariff data
- Battery degradation profiles — approximated from the Geotab 2024 fleet study and Nissan Leaf-specific fleet telemetry; provisional, pending author review.
- Journey ambient temperature — UK monthly means (Met Office 1991–2020 averages); a per-location Open-Meteo refinement is planned.
- Energy tariffs and pump prices — indicative UK figures, refreshed periodically; each carries its own source in the data.
Who stands behind the model
HonestRange's physics model is authored by a BEV powertrain researcher at the University of East London (School of Architecture, Computing and Engineering), whose work centres on Simulink/Simscape vehicle energy simulation validated against ANL dynamometer test data. Full fixture-level validation against that reference dataset is in progress.
- The author's validated BEV powertrain models are publicly available on GitHub.
- → ORCID: to be linked before launch
- → Publications: to be added upon journal acceptance
The methodology here is published in full rather than peer-reviewed — you can see exactly how every number is produced and judge it for yourself.