I just ordered some 18x9 Cobra R wheels with 30mm offset. Has anybody tried it yet? I know 24mm stick out juuuuust a hair, and these will be roughly 1/4 inch closer so i'm thinkin it should work out. I'm running 275's all the way around. I'd really like to see some pics of anybody with 24mm's

 

You'll be fine because its a 9" wide wheel. I't'll be inside the fender by a few mm. -Andrew

 

I know with my 18X9.5 inch GT500 wheels I bought from discount tire with a 24mm offset, the back wheels stuck out almost a full inch. I know my wheels are 1/2" wider than yours, but I ended up having to get the 50mm offset GT500 wheels from americanmuscle.com to make it all look right. I have 255's in front and 285's in back and they look good now.

You would have 1/4" (roughly 6mm)for half of the wheel width difference + 6mm for the offset difference (30-24)+ 5mm for half of the 275 vs 285 tire width difference for a total of 17mm. 25.4mm is 1 inch so I would thinkyou would have roughly 8.4mm sticking out (1/3 inch) as compared to my roughly 25.4mm. (1 inch)

This is all just a guess, but someone with pictures of the exact setup would definately help out more than just my guess...