There are 3 principles I live by when it comes to fitting tires to rims.
1.) Width: Proper tire/wheel matching must follow the 'Width Principle'. That principle is the tire cross section must be equal to, or larger, than the wheel width plus 1 inch when the wheel with is converted to the metric measure meant the tire width represents. EXAMPLE - 8" wheel + 1" = 9" or 228.6mm. The tire MUST be 228.6mm or larger to look right on the wheel.
2.) Sidewall Height: My 'Sidewall Height Principle' dictates that, regardless of wheel diameter, the vertical sidewall height of the front tire must not be taller than the vertical sidewall height of the rear tire. The rear sidewall height must be equal to ,or taller, than the front sidewall height. Few things look worse than this situation when the front tire has more sidewall height than the rear.
3.) Sidewall Buldge: This last principle, the 'Sidewall Buldge Principle", is similar to the 'Sidewall Height Principle'. The sidewall buldge of the front tire must not be more than the sidewall buldge of the rear tire. The rear sidewall buldge must be equal to ,or more, than the front sidewall buldge. Again, few things look worse than this situation when the front tire sidewall buldge is wider than the rear sidewall buldge.