Above Post , Vehicle WEIGHT Loaded Tire , measure to center of your Axle HUB to Ground . Thats what your RADIAL Tire height is and what Your Speedo sees driving down the Road ! Try this one , a 1969 GTS 383 4 speed , with 3.91s in the rear , with 235 / 60 / 14 s that measure 22.5" tall, MABE 11.25 to the Center axle hub . You bet It's NOT running the recommended speedo gear to drive MILE Marker , to MILE Marker ! But I have speedo Dead nuts perfect using 2 mile markers , or even with Phone GPS !