[Arct1k]

14-16T would be a good start...

Differential Ratio: 4.3
Transmission Ratio: 1
Other Ratio: 1
Spur Tooth Count: 46
Pinion Tooth Count: 16
Total Voltage: 14.8
Motor KV: 1853
Tire Diameter (inches): 5.8
Tire Ballooning (inches): 0
Motor Current Draw: 0
Motor coil Ω: 0.0092
Spur/Pinion Ratio: 2.88 : 1
Total Ratio: 12.3625 : 1
Tire Circumference (inches): 18.22 inches (462.82 mm)
Total Motor Speed: 27424.4 RPM
Vehicle Speed: 38.28 mph (61.49 km/h)
Effective Speed Rate: 2.59 mph/V (4.15 kmh/V)
Estimated Adjusted Speed: 36 mph (58 km/h) - 5% loss
Effective KV Value: 1853