The Main Quality Issues in Tire Retreading

What matters most in retreading is quality and safety — sound quality is the basis of safety. Common problems come mainly from four sources: the casing itself, the repair craft, the raw materials, and cure temperature and pressure.

First, the casing. Casings with too many injuries (say more than 5), a single injury too large (say over 5 cm), bead damage, or ply damage are generally not fit to retread. Whether a casing can be retreaded is usually judged by tapping and listening, and a tire spreader and spark tester can aid the inspection for a more reliable call.

Second, the repair craft. Repairs are external and internal. Buffing should follow the cord direction and avoid harming the cushion and belt layers; a patch must be centered on the damage with about 10 mm of margin on each side. Poor craft plants the seeds of separation and air leakage.

Third, raw materials. Tread rubber quality directly affects mileage, and cushion gum determines whether tread and casing separate (de-bonding). Chasing the lowest price with poor material is usually a false economy — on the same size, spending a little more on good material can mean tens of thousands of extra kilometres.

Fourth, cure temperature and pressure. Curing is a chemical reaction sensitive to both: the cushion gum reacts fully only at around 115°C (to about ±1°C) with roughly 8 kg in the tube, 4 kg in the envelope, and 6 kg in the chamber (to within 0.1–0.5 kg). When these are unstable and fall short of — or exceed — the set values, the reaction is incomplete and trapped air causes blistering. A chamber's stable temperature and pressure control is therefore essential.