Downsizing on tires?

Hello everyone! I have a 2001 Chevy Suburban and I'm in need of new tires. It's got a 6" lift and it has all terrain tires that are 305/70-16 (on aftermarket wheels) in size. They're pretty low on tread and I want to replace them. My concern is that I'm on a slightly tight budget and I can't necessarily afford the same size tire. I'm not sure the complete specifications of the aftermarket rims (like the offset) but the sidewall of the tires stick out a bit so I'd assume I'd be able to put smaller width tires on it.Would I be able to downsize on the tires with the aftermarket wheels? I'm a bit concerned because all the tires within that size are only off road tires and we don't even go off road as often. via /r/cars http://ift.tt/2s7sjzk