A large point or purpose of going to a larger diameter wheel is to also get the visual and potential performance enhancement affects of the lower profile tires that come with that conversion. You want to match up the final outer diameter of your new 20” tires to your factory sized ones as close as possible.
For example: 345 30 19 is 27.1” outer diameter but 345 30 20 is 28.1”, 1” too tall. 345 25 20 is 26.8”, .3” under but that is much closer and the number varies by brand.
Use this calculator to see what is best for your car, but confirm actual outer diameter with the tire manufacture’s website:
The best tire size calculator. Use our tire size calculator to find tire size specs and suggested tire sizes. Then check prices for all available tire sizes.
tiresize.com