What Is Thermal Tyre Inspection and How Does It Work?

Thermal signatures precede visible damage by hours to days. A tyre with an active belt separation looks identical to a healthy tyre under visual inspection, but its surface temperature tells a different story. Thermal tyre inspection detects developing faults by mapping surface temperature across the entire tread and sidewall using LWIR cameras operating in the thermal infrared rangerange. Internal faults generate friction and heat that conducts to the surface, creating temperature anomalies visible to FLIR thermal cameras even when the tyre looks normal to the eye.

When a belt separation begins inside an OTR tyre, the separated layers rub against each other under load. This internal friction generates localised heat that conducts outward through the rubber to the tread surface, appearing as a hot spot or circumferential hot streak. The thermal camera converts raw infrared radiation into temperature readings using factory calibration against blackbody reference sources. Rubber has high emissivity (approximately 0.95), so nearly all detected radiation is genuine emission from the tyre rather than environmental reflection.

Initial delamination produces temperatures 15-25 degrees C above undamaged portions of the same tyre. As the separation progresses, the thermal anomaly grows in both temperature and area. Machine learning models trained on thousands of tyre thermal images can identify anomalies as small as 5 degrees C above baseline, catching faults at their earliest detectable stage. The system analyses temperature differentials across the tyre surface rather than absolute temperature, making detection reliable regardless of ambient conditions.

Thermal imaging reveals several failure modes that are invisible to visual inspection, including belt separations, brake drag, bearing failures, and sealed injuries. Each fault type produces a distinctive thermal signature that trained analysts and machine learning models can distinguish.

Belt and tread separations. The most critical fault. A localised hot spot where the casing is delaminating. The separation traps heat beneath the rubber surface, and that heat conducts outward. On a thermal image, a distinct bright zone appears on the tyre face at temperatures significantly higher than the surrounding rubber.

Brake drag. Extreme heat at the wheel assembly, visible at the brake rotor, caliper, or drum. A truck with one brake dragging shows that wheel significantly hotter than the others. The thermal contrast is unmistakable.

Bearing failures. A failing bearing generates heat at the hub, which conducts through the wheel into the tyre and appears as a hot spot at the wheel end. Thermal imaging provides an independent check that complements bearing temperature sensors.

Sealed versus venting injuries. A sealed injury (where rubber closes around the damage) traps heat beneath the surface. Internal temperature can keep rising without external cooling, creating a fire risk. A venting injury releases heat to the air. Both require action, but sealed injuries are more urgent because the thermal build-up is hidden.

Failing tyres generate heat because internal structural damage creates friction zones that convert mechanical energy into thermal energy with every wheel rotation. A damaged tyre pumps progressively more heat into the fault zone, and the process accelerates until the casing fails catastrophically.

The primary heat generation mechanism in a failing OTR tyre is belt separation. This begins at the shoulder area where flexion and heat concentration are greatest. Under normal operation, an OTR haul truck tyre runs at surface temperatures between 60 and 80 degrees C. When the belts begin to separate, internal rubbing and flexion in the damaged zone push local temperatures above 80 degrees C. A localised zone persistently running 20 or more degrees above the surrounding tread indicates developing structural failure.

Tyre manufacturers rate each tyre for Tonne-Kilometres Per Hour (TKPH), which is a thermal capacity limit. Exceeding TKPH causes internal heat build-up with zero external warning signs visible to the human eye. The temperature in the affected zone can reach 20-50 degrees C above normal operating range. Once the fault zone reaches thermal runaway, the failure progresses rapidly toward blowout or fire. The entire process from initiation to catastrophic failure can take days to weeks, creating a viable window for thermal detection and intervention.

External thermal detection catches faults that TPMS misses because belt separations and tread delaminations generate heat in the tread and belt layers, not in the air chamber where TPMS sensors sit. On ultra-class OTR tyres, up to 180mm of rubber, steel belts, and casing material separates the internal chamber from the outer tread surface, creating a significant insulating barrier.

Rubber has a thermal conductivity of just 0.15 W/m K, roughly 300 times less conductive than steel. A belt separation generating significant heat in the tread area can exist for days before the internal air chamber temperature rises enough for a TPMS sensor to register an alert. In many cases, the tyre fails structurally before the pressure or temperature change reaches the TPMS threshold. This insulating effect is why pressure-based monitoring alone cannot provide early warning of heat-driven failure modes.

TPMS excels at detecting underinflation and slow pressure leaks. External thermal imaging excels at detecting structural failures, belt separations, and TKPH exceedance. The two technologies detect fundamentally different failure modes. A tyre can be at correct pressure and still have an active belt separation that will destroy it within days. Learn more about how these technologies compare in TPMS vs External Thermal Monitoring: What Each System Detects.

A thermal camera’s ability to measure a hot spot accurately depends on how many pixels cover the target area. The industry working standard requires approximately 5×5 pixels covering the smallest feature to be detected. Below that threshold, the hot spot blends with cooler surrounding rubber and the reading understates the true temperature.

At any given distance, a higher-resolution camera delivers more accurate measurements. A 640×480 sensor covers a 2cm hot spot with 9-12 pixels at 3 metres, producing a stable reading. A 320×240 sensor at the same distance covers the same spot with only 3-4 pixels, introducing noise. If the hot spot is physically smaller than the camera’s instantaneous field of view (IFOV) at the measurement distance, the reading will average the hot spot with its surroundings. Fixed-installation systems eliminate this variable by using a known, consistent measurement distance for every pass.

Thermal imaging can detect tyre delamination 24-48 hours before catastrophic failure, based on published research and field deployment data from Teledyne FLIR. In many cases, the window is longer because belt separation progresses over days to weeks before reaching the critical failure stage.

The detection lead time depends on inspection frequency. A manual thermal scan might catch a fault once per shift or once per day. An autonomous system like the Pitcrew Autonomous Inspection System scans every tyre on every pass, which means a developing fault is tracked across multiple inspections. Each scan builds a thermal history that shows whether the anomaly is growing, stable, or resolved. This sequential tracking enables growth-rate prediction rather than single-point-in-time assessment.

Approximately 90% of OTR tyres never achieve their design life, according to Kal Tire fleet data. Early detection of developing failures extends the usable life of undamaged tyres by preventing cascading damage. It also preserves tyre casings for retreading, which reduces per-tyre costs by up to 31%. Understanding what tyre failures cost mining fleets is the foundation of an effective thermal tyre monitoring programme.

Manual thermal inspection relies on a technician with a handheld infrared camera walking around a parked truck. Each operator brings their own technique, camera settings, and interpretation. One technician might stand 2 metres from the tyre while another stands 5 metres. One sets emissivity to 0.95, another leaves it at the factory default. The same truck inspected by two technicians on different days can produce different conclusions. Manual inspection is also limited by frequency. With 500 trucks in a fleet, manual scans happen weekly or monthly at best, leaving long gaps where failures develop undetected.

Automated systems place thermal cameras at fixed infrastructure beside the haul road. Every truck passes through the same location, so cameras are always at the same distance with the same angles. Parameters are set once during deployment and adjusted seasonally. Environmental factors (atmospheric temperature, humidity, reflected temperature) are measured by on-site sensors and applied automatically. This consistency is the key advantage. Instead of trying to achieve absolute accuracy, the system learns the normal thermal profile for each tyre position on each vehicle and flags deviations from baseline. A tyre suddenly 10 degrees C above its historical average triggers a review, regardless of ambient conditions.

Thermal imaging is not a replacement for existing tyre management systems. It is an additional independent layer of detection. TPMS monitors pressure. Visual inspection catches cuts, bulges, and obvious surface damage. Brake temperature sensors detect brake drag. Each system has blind spots. TPMS does not detect slow internal separations. Visual inspection misses damage inside the casing. Brake sensors do not see tyre defects.

Thermal imaging fills those gaps. A heat separation invisible to TPMS and visual inspection is obvious on a thermal image. Multiple overlapping controls, each covering different failure modes, provide the most complete safety net. This layered approach is especially critical for autonomous haulage system (AHS) fleets, where there is no driver to notice visual signs of damage, smell burning rubber, or feel changes in ride quality. Infrastructure-based thermal inspection provides the continuous monitoring that autonomous operations require.