18” front 20” rears

[1970MonteCarloNH]

Hey guys I’m running 18” fronts and 20” rears can any one help me out with correct tire sizes ? I tried searching the forum before asking this question. 

[Paul C]

in todays sizes about a 225/78/R15  1st number is the width of the tire in mm.  The 2nd number is the tire's profile presented in a percentage of the width, and the 15 is the rim size.  R is for radial, which is the sidewall construction.    

[Traveler]

you might want yo search the forums I have found one where members list their combinations 

[Blackhawk]

We need to know the wheel widths and backspacing/offset before knowing what tire size might work.