The 1991 Isuzu Pickup tire size depends on trim: the LS, 2D Pickup Extra Cab, 4WD takes P205/75R14; the LS, 2D Pickup Extra Cab, RWD, Automatic takes P205/75R14; the LS, 2D Pickup Extra Cab, RWD, Standard, MSG5C takes P205/75R14; the LS, 2D Pickup Extra Cab, RWD, Standard, MUA5C takes P205/75R14; the LS, 2D Pickup, 2.6 E, 4WD takes P205/75R14; the LS, 2D Pickup, 2.6 E, RWD, Automatic takes P205/75R14; the LS, 2D Pickup, 2.6 E, RWD, Standard, MSG5C takes P205/75R14; the LS, 2D Pickup, 2.6 E, RWD, Standard, MUA5C takes P205/75R14; the LS, 2D Pickup, 3.1 Z takes P205/75R14; the S, 2.3 L, MSG5C takes P195/75R14; the S, 2.3 L, MUA5C takes P195/75R14; the S, 3.1 Z takes P225/75R15, per the factory service manual.
Factory-Spec Tire Size
Varies by trim
LS, 2D Pickup Extra Cab, 4WD: P205/75R14
LS, 2D Pickup Extra Cab, RWD, Automatic: P205/75R14
LS, 2D Pickup Extra Cab, RWD, Standard, MSG5C: P205/75R14
LS, 2D Pickup Extra Cab, RWD, Standard, MUA5C: P205/75R14
LS, 2D Pickup, 2.6 E, 4WD: P205/75R14
LS, 2D Pickup, 2.6 E, RWD, Automatic: P205/75R14
LS, 2D Pickup, 2.6 E, RWD, Standard, MSG5C: P205/75R14
LS, 2D Pickup, 2.6 E, RWD, Standard, MUA5C: P205/75R14