Suprahaha,
Basically I am saying the chart will let you know what will work with any of the 4 combinations. Things the chart say won't work, may work with a stock suspension and stock ride height.
AMUSE,
If your running relatively narrow rims like 8.5" front and 9.5" rear with narrow tires 235's front and 275's rear than a smaller offset will allow the tire to be flush with the fender lips. My larger 50mm offset front and 55mm offset rear wheel will allow me to run 275's front and 295's rear. My tires will still be located at about the place as related to the fender lip, but I will need to move the wheels/tires inside to allow for the extra width.
I wouldn't personally run anything smaller than a 9" wide wheel with a 255 on the front of a Surpa. It's very heavy car and it feels much more nimble with more rubber on the front.
The wheel sizes you listed will be somewhat limiting. You won't want to run any bigger than a 235 (possibly a 245) on the front. Given this you have a couple of choices for the rear.
1. Run the maximum size of 285/30 on the rear and have a car that will understeer a lot and not be much fun to drive.
2. Run a 265/35 on the rear and have car that will be balanced, but not have the grip or look you would want after adding new wheels and tires.
The Supra is a car that can run and needs very large wheels/tires. These are not easy to find. Especially when your on a budget. Look at the size wheels/tires cars with the same power and weight of a BPU Supra run and you will get an idea of how under tired the Supra is.
The Enkei RPO1 is still one of the best wheels available for a Supra if your on a budget. You can get an 18x9" 42mm offset 255/35R18 front and 18x9.5" 45mm offset 285/30R18 rear. You can get this whole set of wheels for $720. A friend is looking at buying a Supra. We are going to buy the RPO1's in an 18.9.5" 45mm offset for the front. Then we are going to get some 18x9" 22mm offset and widen them 2". This should give us an 18x11" 47mm offset wheel that can be run without any spacer or extended lug. This should give us some 18x9.5" front and 18x11" rear wheel for less than $1,200. It will be several months, but I will let you know what we find.
Later, Steve