Correcting Speedo after Wheel change.

need rear axle ratio There are charts that give proper gear tooth count based on gear ratio and tire size.

225/60x15 is 25.6" tall.
6.50x13 approx factory tire size 175/70x13 22.6" tall

factory std rear axle ratio is -
auto trans 2.93 gear needed part number 2538930, Yellow, 30 tooth
manual trans 3.23 gear needed part number 2538933, Yellow, 33 tooth

http://www.mymopar.com/speedometer.htm

30 tooth for sale here.
http://www.forabodiesonly.com/mopar/showthread.php?t=262176&highlight=speedometer+gears