Here is a chart. If you think you want to drive on an expressway and enjoy your engine turning 3000 rpms, pick the ratio that does that. Just remember that x way speeds ain't 55 anymore. If you want to enjoy driving with your engine turning 1800/2000 rpms at 70/80 mph..........then pick the gear that does that. Its that simple. One point......I have never heard anyone complain about their engine quietly turning 1800 rpms for an hours long drive. Note: This chart is for only 60 mph so err on the side of a lower numerical ratio if you plan to drive faster on the xway.