Have you considered set of AO50's in your current size first? The people I know who have gone from the Hankooks to them say they would not go back to Hankook, not because they are shit but because the yoki's are that much better in terms of lateral grip.

If 10 inch wide rims can be fitted to a GC (Roughstilin) then I reckon it can be done to a Foz. If you saw the pics in my build thread my tyres are rubbing the arch liners that are 10mm away from the tyre surface. Your car probably wouldn't flex as much because you have deleted all the rubber mountings but you still don't want your tyre/rim less than 5mm from the strut from what I have been told.

Have you had a chat with John Fowler? I went through this with him about my Betty and he recommended staying with my oem size rims as weight starts becoming a factor at my modest power level and the sprint racing I am interested in is a bit more about chucking the car around and having fun.

A dedicated Barbs car you might see gains but not sure for sprint series/rally style events.

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Bye bye betty blue. Hello F6.