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Which widebody do you have? Do you know exactly how much wider it is?
If you a serious about going with 305 R-comps the stock brembos won't cut it. You'll need a BBK which will require you to with 18s. 18x10 +25 is a good starting point. 305/30/18 is matches the stock size almost exactly. A quick search on tirerack says that only v700s come in that size. You can always go slightly smaller with 275 or 285 and open up more tires choices.