Spare Tyre

The spare tyre is a backup tyre carried in the vehicle for use following a tyre failure requiring immediate wheel replacement. Three types are used in modern vehicles: a full-size matching spare (identical to the regular tyres, can be used indefinitely and incorporated into the rotation schedule); a full-size non-matching spare (correct diameter but different tread pattern or brand, usable until a matching replacement is obtained); and a temporary spare (a narrower, smaller diameter ‘space-saver’ spare, clearly marked with its maximum speed of 80 km/h and a typical maximum range of 80–100 km). Many modern vehicles — particularly those fitted with run-flat tyres, small crossovers, and electric vehicles — are supplied without any spare tyre, carrying only a tyre inflation kit (puncture sealant and compressor) that can address minor tread punctures but cannot address sidewall damage, blowouts, or wheel damage.

The spare tyre provides immediate mobility after a tyre failure that cannot be addressed with a puncture repair or run-flat continuation. A full-size spare offers full performance immediately; a temporary spare imposes strict speed and distance limits but allows the vehicle to reach a tyre repair facility. The spare tyre's availability and condition are most critical during motorway driving at night, in remote areas, or in adverse weather — the situations where a tyre failure is most dangerous and roadside assistance is slowest. Vehicles without spare tyres and carrying only puncture sealant kits are completely immobilised by any failure mode that sealant cannot address: sidewall blowouts, valve stem failures, wheel rim damage, or tyre damage requiring inspection before sealing.

Spare tyre found flat when needed in an emergency: Natural pressure permeation over months and years reduces spare tyre pressure below safe inflation — a spare tyre that has never been checked since vehicle purchase may be at 0.5–1.0 bar. The spare is typically the last tyre checked during monthly pressure inspections, and is often at a different pressure specification from the road tyres.

Temporary spare fitted to the front axle of a front-wheel-drive vehicle: The temporary spare's reduced grip and different handling characteristics are most dangerous at the steered and driven axle. Fit the temporary spare at the rear position if possible, moving the best road tyre to the front.

Tyre inflation kit sealant having expired or having been used: Puncture sealant has a shelf life of approximately 4 years and cannot be used twice. Check the sealant expiry date printed on the canister. A used or expired sealant kit provides no emergency capability.

Level 1 — Owner check: Check spare tyre pressure monthly alongside the road tyres. The spare tyre pressure specification is usually different from the road tyres — typically 4.2 bar (60 psi) for a temporary space-saver spare, and the same as the road tyre specification for a full-size spare. Confirm the pressure specification from the owner’s manual or the tyre itself. Check sealant kit expiry date annually.

Level 2 — Detection: Inspect the spare tyre's tread depth and sidewall condition at every tyre rotation. A spare tyre that has been stored in the boot for several years may have sidewall cracking from ozone degradation even without use — a degraded spare provides false confidence. Include the spare in the age assessment — if the road tyres are being replaced for age, consider whether the spare requires simultaneous replacement.

Level 3 — Professional service: A full-size matching spare should be incorporated into the tyre rotation schedule as the fifth tyre — this equalises wear across all five tyres and extends the tyre set’s total lifespan. A temporary spare cannot be rotated into service — it is exclusively a breakdown spare.