ISO 7975:2019

Overview

ISO 7975:2019, "Passenger cars - Braking in a turn - Open‑loop test method", specifies a repeatable open‑loop test procedure to quantify how a braking action alters a vehicle’s steady‑state circular response. The method applies to passenger cars (ISO 3833) and light trucks and is intended to produce controlled, discriminatory measures of braking behaviour in a turn. The manoeuvre is deliberately not representative of everyday driving but is useful for controlled evaluation of vehicle dynamics and brake system effects, including recognition of regenerative braking and active control systems.

Key topics and technical requirements

• Test principle: Start from a steady‑state circular run (constant longitudinal speed and fixed steering wheel angle) and apply a controlled brake input while recording driver input and vehicle response.
• Measured variables (minimum): moment of brake application, steering‑wheel angle, lateral acceleration, longitudinal acceleration, longitudinal velocity, yaw velocity, sideslip angle (and/or lateral velocity). Recommended additional measurements: brake system pressure and wheel rotational speed.
• Measuring equipment and accuracy: ISO 15037‑1:2019 measurement and data‑processing requirements apply. The standard specifies recommended accuracies (e.g., moment of brake application detection to ±0.05 s; brake pressure measurement accuracy guidance).
• Brake conditioning and warm‑up:
  • Disc/disc systems: 60 run‑in brake applications from 100 → ~20 km/h with staged decelerations (approx. 2, 3, 5 m/s²).
  • Disc/drum or drum/drum systems: 200 applications with staged decelerations.
  • Warm‑up: tyre and component warm‑up per ISO 15037‑1 and five full stops to engage ABS during warm‑up.
• Brake temperature limits: front discs/drums 80–120 °C before each test; rear <120 °C. Cooling between runs as needed.
• Path geometry: Standard test radius is 100 m (additional radii 30–200 m may be used). Initial conditions follow ISO 4138 steady‑state circular test requirements.
• Data evaluation: Time histories, reference time for brake application, mean longitudinal acceleration calculations and presentation of characteristic values (Annex A provides presentation format).

Applications and users

Practical uses include:

• Vehicle dynamics validation and comparison of braking influence on cornering stability.
• Brake system development and calibration (including regenerative braking and ABS/ESC tuning).
• Active safety system design and verification (ESC, stability control).
• Independent test laboratories, OEM vehicle dynamics and chassis engineers, brake and tire manufacturers, and regulatory or certification bodies seeking controlled, repeatable metrics.

Related standards

• ISO 4138 - Steady‑state circular driving behaviour (open‑loop methods)
• ISO 15037‑1:2019 - Vehicle dynamics test methods - general conditions
• ISO 8855 - Vehicle dynamics vocabulary

Keywords: ISO 7975:2019, braking in a turn, open‑loop test method, passenger cars, vehicle dynamics, steady‑state circular response, brake conditioning, brake temperature.