In early 1973, following problems with the wheel treads on class 86 locomotives shedding small pieces of metal (tyre shelling), a wide-ranging investigation including various modifications was put in place. As part of this programme the Testing Section were asked to undertake a series of running and braking tests to determine the causes.

The problem was thought to be due to the malfunctioning of the electric (rheostatic) brakes which resulted in the friction brakes being applied at high speed rather than blending-in as the rheo became less effective at lower speeds. The result of this application was to generate high temperatures on the wheel tread which changed the molecular composition of the steel making it brittle. Prolonged repetition of the malfunction resulted in tyre shelling.

Included in the programme was the monitoring of the tyres of a selected locomotive over a prolonged period, running under test conditions with reduced brake pressures, isolated rheostatic brake etc. We undertook a series of tests running between Crewe and Willesden with the class 86 locomotive under test being hauled by another locomotive.

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