newbie... is there a way the average slug can measure for rim size

[game-over]

i have a 69 camaro and want to order some 17's possibly 18's.
i have an idea what size the rims need to be but i want to be sure.

any particular way i can measure correctly. I would hate to take the word of someone and eat $2500 for rims.

it is stock tubs with DSE 2" drop leaf springs and stock front with suspesion with DSE replacment and 2" drop springs.
rear disc conversion from right stuff which adds 1/4" on each side or something like that .

i want to run 275's..

i have 275/50/15's on it now with 15" x8 rallys 5" bs and nothing rubs..


any suggestions with what i can do to make this a 100% for me...

[Track Junky]

You can get 17 & 18/275's with a 5.5" backspace and you will be fine as long as you don't lower the car too much. More an issue up front than rear. With a 5.5" back space you will rub frame when steering loc-to-loc but not enough to be an issue. If you lower the car too much in the front with 5.5" backspace you will rub upper/outer front fender wells. Don't remember what the safe height is but I'm pretty sure if you drop only 2" all the way around you should be fine.

[Vince@Meanstreets]

Try to find a shop that can test fit a wheel combination or rent a back space tool. All cars are different and may require different sizing.