T (temporary spare tire)

How to read it

In T125/80R15 or T145/80D16, T is the prefix. Ford’s owner’s manual describes it as a Tire and Rim Association designation for tires intended for temporary service on cars, SUVs, minivans and light trucks, and Yokohama as a temporary spare or mini-spare, designed to be used only until a flat tire can be repaired or replaced. The rest of the size reads as usual, though a D in place of R, as in Ford’s example, means diagonal (bias) construction. Bridgestone’s manual gives T125/80R15 95M as an example: load index 95 and speed symbol M, which is 130 km/h (81 mph). Pirelli’s speed chart lists M for temporary spare tires.

Also searched as: donut spare, space saver, T125/70D16.

Pressure

USTMA and Bridgestone both give 420 kPa (60 psi) as the pressure for T-type spares; Bridgestone says this applies in all uses, whether the spare is light load or standard load. FMVSS 109 requires any tire with a maximum pressure of 420 kPa (60 psi) to carry the words “Inflate to 420 kPa (60 psi)” on both sidewalls, in letters at least 12.7 mm (1/2 inch) high.

Limits on its use

USTMA says there may be restrictions on the speed, distance and position of a temporary spare, set out in the vehicle owner’s manual, and that T-type spares are for use only on rims or wheels made for them. Ford’s manual defines a temporary spare as one that differs from the road tires in diameter, width, tread or maker, and points to the tire label or Safety Compliance label for its limits.

Standards

FMVSS 139, the standard for car and light truck tires, excludes radial T-type spares; they come under FMVSS 109, and FMVSS 110 lets passenger cars be equipped with them. A non-pneumatic (airless) spare is a different kind, and FMVSS 110 requires it to be marked FOR TEMPORARY USE ONLY and MAXIMUM 80 KM/H (50 M.P.H.). Ford’s manual notes the federal quality grades do not apply to temporary spares. The same letter at the other end of a service description, as in 95T, is a speed rating.