Wheel width is also a factor. The above statement is only true if both wheels are 7.5" width. Easiest way to think of offset is the wheel center line. For example only, a 9.5" +45 wheel will stick out 1" further than a 7.5" +45 wheel. It will also sit inboard an additional 1".
Definitely stick with 40 sidewall, regardless of 225 or 235 width.
I know what wheel offset is. But given that a 235 is 10mm wider than 225, which sits just about flush on a 7.5 wheel, a 235 will be nearly flush on an 8, which is 12.7mm wider than a 7.5. All in all, he should be fine with an et45 and a 225, because it's the tire that forms the outermost boundary of the rotating object that has to fit inside the wheel well, as it's just a 4mm offset from stock. If he slaps on 9" wheels with a 225, it should still be fine, but the tires will look out of place. I, on the other hand, will most likely have to do the fender screw mod because I'm going with 235.
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