The 1998 Nissan Frontier tire size depends on trim: the Base takes P215/65R15 95S; the SE, 4WD takes P215/75R15 100S; the SE, RWD, Automatic takes P215/65R15 95S; the XE, 2D Pickup Extra Cab, 4WD takes P215/75R15 100S; the SE, RWD, Standard takes P215/65R15 95S; the XE, 2D Pickup Extra Cab, RWD, Automatic takes P215/65R15 95S; the XE, 2D Pickup Extra Cab, RWD, Standard takes P215/65R15 95S; the XE, 2D Pickup, 4WD takes P215/75R15 100S; the XE, 2D Pickup, RWD, Automatic takes P215/65R15 95S; the XE, 2D Pickup, RWD, Standard takes P215/65R15 95S, per the factory service manual.
Factory-Spec Tire Size
Varies by trim
Base: P215/65R15 95S
SE, 4WD: P215/75R15 100S
SE, RWD, Automatic: P215/65R15 95S
XE, 2D Pickup Extra Cab, 4WD: P215/75R15 100S
SE, RWD, Standard: P215/65R15 95S
XE, 2D Pickup Extra Cab, RWD, Automatic: P215/65R15 95S
XE, 2D Pickup Extra Cab, RWD, Standard: P215/65R15 95S