How Lab Range Is Measured: Inside the ISO 7176-4 Energy Consumption Test

One chair claims 25 km, another 45 km, and in real use both die at 18. The gap is not always dishonesty — it is usually different test conditions. The industry reference method is ISO 7176-4, and understanding it takes ten minutes and saves you from every inflated range claim on the market.

The drum test

The chair is secured on a roller dynamometer (drum), loaded with a test dummy, and driven at constant speed until the battery reaches its cutoff voltage. Energy consumed and distance traveled are recorded. Because the drum has no wind, no stops, no kerbs, no temperature swings and no user fidgeting, it is a best-case number by construction. Consumer mix-cycle driving typically realizes 50-70% of drum range.

Four variables labs quietly change

• Dummy mass: 50 kg dummies are permitted for lighter chairs; a 100 kg dummy can cut range 15-25% on the same hardware.
• Speed: range at maximum speed is 20-30% lower than at the efficiency sweet spot (usually 4-6 km/h).
• Cutoff definition: stopping at the controller's low-voltage limit versus "battery fully exhausted" can differ by several kilometers.
• Temperature: lithium packs deliver 70-85% of rated capacity at 0 degrees C versus 25 degrees C.

The conversion we recommend

Take the claimed range, apply 0.6 as a default factor, then adjust: subtract 10% for every 20 kg of user mass above 80 kg; subtract 10% for hilly terrain; subtract 20-30% in winter. A "30 km" chair with a 95 kg user in a hilly town in January is realistically a 13-15 km chair. Plan charging around that number, not the brochure.

What honest reporting looks like

Our published ranges are drum-test values at 100 kg dummy and 6 km/h, with the factor-based estimate shown alongside in quotation documents. If a supplier cannot state dummy mass, speed and cutoff when asked, treat their range figure as decorative.

One number worth asking for instead

Energy consumption per kilometer (Wh/km) is harder to game: mid-drive folding chairs typically consume 11-16 Wh/km on the drum; rear-drive with heavier frames, 16-22 Wh/km. Divide usable battery watt-hours by Wh/km and you get a range estimate you can defend — across any brand, any brochure.