Tyre maintenance — when to check inflation pressure At what temperature condition should tyre inflation pressure be checked to obtain an accurate ''cold'' reading for road vehicles?

Introduction / Context:
Tyre pressure recommendations assume a 'cold' tyre, meaning the tyre has been parked long enough to return to ambient temperature. Checking at the correct condition ensures load capacity, handling, wear, and fuel economy meet design targets.

Given Data / Assumptions:

• Ambient (surrounding) temperature may vary by climate and season.
• Vehicle has been stationary for several hours or driven less than a few kilometers at low speed.
• Gauge measures absolute or gauge pressure consistently.

Concept / Approach:
Tyre pressure rises with temperature due to gas expansion. OEM placard pressures are specified for 'cold' conditions at the current ambient, not at a fixed laboratory temperature. Therefore, the correct condition is to measure at ambient temperature with tyres cooled to that temperature.

Step-by-Step Solution:
Park the vehicle and let tyres cool to ambient (typically 2–3 hours).Measure pressure and adjust to placard values.If measured hot, apply manufacturer hot-to-cold correction or recheck later.

Verification / Alternative check:
Ideal gas relation indicates pressure increase as temperature rises; after highway driving, measured pressure will be higher than the cold specification.

Why Other Options Are Wrong:
Fixed temperatures like 20°C, 25°C, or 35°C are not universally applicable; placards are not tied to a single fixed temperature in real-world use.

Checking at 50°C (hot) gives misleading readings relative to cold specification.

Common Pitfalls:
Bleeding air from hot tyres to match cold specs (leads to underinflation when tyres cool); ignoring seasonal changes that warrant adjustments.

Final Answer:
ambient temperature