Final Drive Gear Ratio

The original sprockets on my Triumph were an 18 tooth sprocket up front with 43 teeth at the rear. Running 17/47 sprockets gives me 70 mph indicated at 4500 rpm in top gear. 70 mph indicated is 60 mph measured at least on my bike, running a 3.50 x19 Shinko Trials tire up front and a 5.10 x 17 Kenda K270 on the back. When I had 16/44 sprockets on the bike it was about the same; an adequate compromise between highway and dirt, still a bit tall for offroad with a sidecar.