I show the following true fifth gear numbers for a Speedmaster with factory sized rubber, and 43 tooth rear sprocket, as corrected for the plentiful speedo errors. I do believe the data is the same for the America.
60 mph
17 = 3700 rpm (59 mph)
18 = 3500 rpm (59 mph)
19 = 3400 rpm (60 mph)
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70 mph
17 = 4400 rpm (70 mph)
18 = 4200 rpm (71 mph)
19 = 3860 rpm (69 mph)
Our factory tachs are usually off a bit at around + or - x one hundred or so RPMs, but the above is the basic math, rounded to the nearest whole numbers for MPH.
My 05 Speedmaster speedo usually reports around 5 to 7 mph faster than actual MPH, as supported by both the above and also the roadside radar boxes.
