not sure about the available offsets, but et30 wouldn't work out well with adapters. stacy's fronts are 18x8 et21, so at a minimum, they'd poke 6mm more (most adapters are a minimum of 15mm). she runs a 205/40.
as for the et50, you're still going to have some problems with such a large tire. a 225/40 on an 18x8 is going to be very square and can't be anywhere near the fender in the front. after a 15mm adapter, it'll be et35, which will likely still rub with a 225/40 unless you raise your coils quite a bit. with a smaller tire, et35 isn't a problem.
another thing to consider is the cost and hassle involved with adapters. most good adapters are going to run $350+. they can also be a pain to deal with if you have a flat, as you have to pull the adapter to mount the spare. for me, i had to have someone press the brakes to be able to pull the adapter.
Last edited by motocaddy; 08-16-2011 at 06:04 PM.