If the sticker is still on the driver's door opening you should see a size listed. On my '86 Ramcharger 2WD I think it is 205/75R15 IIRC.

1986 Dodge Ramcharger 440 2wd, Bracket Racer Under Construction
1998 Ram 2500 QuadCab, new daily driver.
2008 Honda Element
2014 Carry-On 7x14 Cargo Trailer