VTX1800 N with VTX1300 Final

My 1800N has a stock rear wheel which has an 180/70 tire. That means it is 180 mm wide. Since the aspect ratio is 70%, that means the distance from the ground to the rim is

180 x 0.7 = 126 millimeters or 12.6 centimeters. Since 1” = 2.54 centimeters the ground to wheel distance is 12.6 / 2.54 = 4.96”. The tire diameter is 4.96 x 2 (top+bottom) plus the wheel diameter of 16” for a total of 25.92”. The tire circumference is Pi times Diameter (Pi = 3.1416) therefore we have 25.92 x 3.1416 which is 81.43 inches. Divide that by 12 inches and for each tire rotation, the bike will travel 6.786 feet. In one mile the tire will rotate 5280 / 6.786 = 778.07 revolutions. For sake of simplicity, I will calculate the engine revolutions per minute for the various gears at 60 mph since it takes one minute to travel one mile at that speed.

Since the Primary and Final Reduction ration are always the same, we’ll calculate the overall first. 1.571 x 2.818 = 4.427

1^{st} Gear = 2.353

2^{nd} Gear = 1.478

3^{rd} Gear = 1.111

4^{th} Gear = 0.871

5^{th} Gear = 0.697

At 60 mph:

5^{th} Gear 778.07 x
4.427 x 0.697 = 2400 rpm

4^{th} Gear 778.07 x
4.427 x 0.871 = 3000 rpm

3^{th} Gear 778.07 x
4.427 x 1.111 = 3830 rpm

2^{nd} Gear 778.07 x
4.427 x 1.478 = 5090 rpm

1^{st} Gear 778.07 x 4.427
x 2.353 = 8105 rpm

At 5,000 rpm:

1^{st} Gear 5000 / 8105 x
60 = 40 mph

2^{nd} Gear 5000 / 5090 x
60 = 60 mph

3^{rd} Gear 5000 / 3830 x
60 = 80 mph

4^{th} Gear 5000 / 3000 x
60 = 100 mph

5^{th} Gear 5000 / 2400 x
60 = 125 mph