The 2003 Toyota Tundra tire size depends on trim: the Base, Automatic takes P245/70R16 106S; the Base, Standard takes P245/70R16 106S; the Limited, 4WD takes P265/65R17 110S; the Limited, RWD takes P265/65R17 110S; the SR5, 2D Pickup takes P245/70R16 106S; the SR5, 4D Pickup Extra Cab, 3.4 N, 4WD, Automatic takes P245/70R16 106S; the SR5, 4D Pickup Extra Cab, 3.4 N, 4WD, Standard takes P245/70R16 106S; the SR5, 4D Pickup Extra Cab, 3.4 N, RWD, Automatic takes P245/70R16 106S; the SR5, 4D Pickup Extra Cab, 3.4 N, RWD, Standard takes P245/70R16 106S; the SR5, 4D Pickup Extra Cab, 4.7 T, 4WD takes P245/70R16 106S; the SR5, 4D Pickup Extra Cab, 4.7 T, RWD takes P245/70R16 106S, per the factory service manual.
Factory-Spec Tire Size
Varies by trim
Base, Automatic: P245/70R16 106S
Base, Standard: P245/70R16 106S
Limited, 4WD: P265/65R17 110S
Limited, RWD: P265/65R17 110S
SR5, 2D Pickup: P245/70R16 106S
SR5, 4D Pickup Extra Cab, 3.4 N, 4WD, Automatic: P245/70R16 106S
SR5, 4D Pickup Extra Cab, 3.4 N, 4WD, Standard: P245/70R16 106S
SR5, 4D Pickup Extra Cab, 3.4 N, RWD, Automatic: P245/70R16 106S
SR5, 4D Pickup Extra Cab, 3.4 N, RWD, Standard: P245/70R16 106S
SR5, 4D Pickup Extra Cab, 4.7 T, 4WD: P245/70R16 106S
SR5, 4D Pickup Extra Cab, 4.7 T, RWD: P245/70R16 106S