[lincpimp]

Here is the calc readings with your first setup with the stock spur:

Differential Ratio: 3.3076923076923075
Transmission Ratio: 1
Other Ratio: 1
Spur Tooth Count: 62
Pinion Tooth Count: 16
Total Voltage: 18.5
Motor KV: 1390
Tire Diameter (inches): 5.75
Tire Ballooning (inches): 0
Motor Current Draw: 0
Motor coil Ω: 0.0164
Spur/Pinion Ratio: 3.88 : 1
Total Ratio: 12.81731 : 1
Tire Circumference (inches): 18.06 inches (458.83 mm)
Total Motor Speed: 25715 RPM
Vehicle Speed: 34.32 mph (55.13 km/h)
Effective Speed Rate: 1.86 mph/V (2.98 kmh/V)
Estimated Adjusted Speed: 33 mph (53 km/h) - 4% loss
Effective KV Value: 1390

35mph is pretty good, especially for racing.

Here is the setup with the kyosh spur and 12t pinion

Differential Ratio: 3.3076923076923075
Transmission Ratio: 1
Other Ratio: 1
Spur Tooth Count: 46
Pinion Tooth Count: 12
Total Voltage: 18.5
Motor KV: 1390
Tire Diameter (inches): 5.75
Tire Ballooning (inches): 0
Motor Current Draw: 0
Motor coil Ω: 0.0164
Spur/Pinion Ratio: 3.83 : 1
Total Ratio: 12.67949 : 1
Tire Circumference (inches): 18.06 inches (458.83 mm)
Total Motor Speed: 25715 RPM
Vehicle Speed: 34.69 mph (55.73 km/h)
Effective Speed Rate: 1.88 mph/V (3.01 kmh/V)
Estimated Adjusted Speed: 33 mph (53 km/h) - 4% loss
Effective KV Value: 1390

Pretty much the same as the stock spur.