Agreed, a 245 width tire is the same section width no matter the aspect ratio ... but a shorter sidewall tire will have less flex to go on a narrower rim. When I look in a few of the tire catalogues here, most of the manufacturers are showing an acceptable rim range of 7 to 8-1/2 for the 245-50-17, and 7-1/2 to 9 for 245-45-17.
cheers
Ed N.