Idk how wide you can go without rubbing but the wider the tire you have the wider the rim you need the only complicated things are that tires are measured in millimeters and rims are measured in inches, And that some of a tires width goes into the profile hight and some of the hight into the width depending on how wide of rim you put it on. That tire calculator I posted tells you the recommended rim widths for the tire width you chose. I would try to get the middle one like if it says 7.5"-9" rim get a 8" or 8.5", or if it says 7"-8" get a 7.5" rim.