I believe I have heard of it being done. 225's in Kumho's are skinnier than 225 Hoosiers and I have heard (HEARD mind you) that if you flare the fender wells a bit and accept that you can not turn near wheel lock you can get 225 R15 Hoosiers on. A 205 Hoosier is about the width of a 225 Kumho. Same goes for the Hankook Z214's at 225 compared to a Hoosier 205.
There might be some rub though on the rear trailing arms which is why I have also heard in order to be able to run 225 R15's you need a large spring rate in the rear (heard 1000#'s). This is to prevent the car from leaning over the tire and instead lean the tire over with the lean of the car. It is also nick-named knife edge driving at that spring rate because the car will tend to hook around corners but if you get it wrong you end up pointed the wrong way.
2012 Third Place ITA Great Lakes Division
1990 Honda CRX Si (ITA)
2007 BMW X3 Sport (Stop Light Time Trials)
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