Tyre Second Use, Two Routes Priced in One Account: Retreading Keeps a Third of Casings, Pyrolysis Breaks Even Only on Paper It Cannot Cash

A worn truck tyre has two widely promoted second uses: retreading the casing, and pyrolysis into oil, char, gas and steel. This paper prices both routes in one account, from the accompanying computation. For retreading, an eligibility cascade applied to a stated fleet of 1,000 casings presented for assessment — age, fatal damage, fatigue life, repairable damage, and a final shearography inspection — leaves 372 casings eligible, a fraction of 37.2 per cent. Each retread saves 2,250 MJ against a new tyre (70.3 per cent) and $335 in purchase cost, giving a fleet saving of 837 GJ and a sound route for the eligible minority. The bound is two retread lives per casing: a casing over 7 years old or beyond two prior lives is excluded regardless of how good its tread looks. For pyrolysis, one tonne of tyres yields 420 kg of oil, 350 kg of char, 130 kg of gas and 100 kg of steel. The gas alone (4.94 GJ) covers the 3.8 GJ process heat demand, and 18.78 GJ per tonne is exportable if the char is not burned. Against that favourable energy account stands the residue and the cash: only 192.5 kg of the char is marketable as low-grade filler, 157.5 kg per tonne of feed goes to landfill, and total revenue of $272.86 per tonne falls short of costs of $275 per tonne, a margin of −$2.14 per tonne before transport is counted. Pyrolysis is therefore not an energy failure but an economic and residue failure at the stated prices: it converts a tyre problem into an oil income that almost pays, plus a char disposal problem that does not go away. SIMULATED, NOT MEASURED.