So I’ve finally gotten my 37 Hudson Coupe back on the road after close to 2 decades of sitting. During that hiatus one of my rear tires sidewall bubbled & thus I threw on a trailer tire to move it around with. Now I have one tire at 225/75/15 (28.3” diameter) & other is a 205/75/15 (27.1” diameter). Since it has an open differential (Ford 7.5”), I said to myself I have to test drive it & did yesterday.... Greatest day EVER! So my question is....does anyone know which size tire I’m getting my speedometer & rpm based upon? (and yes new tires before I drive it again, I promise!) Sent from my iPhone using H.A.M.B.