[decooney]

The final dimension also depends on the width of your body iteself. You can rub on the inside if you go too narrow and rub on the outside if you go too wide. I narrowed my Unique/IRS Jag 427 Cobra rear to 52.5" and my ERA IRS 427 rear built to spec at 52.5". Both cars run Trigo wheels with 5 pin adapter hubs. Good luck. I recommend lots of measuring, remeasuring and mock-ups with the car sitting/loaded to be certain about what to narrow it to for your tire width and body type.