Medusa Research

[suicideneil]

Pete- Use the calculator, it is your friend & greatest tool known to man & noob-kind:

http://www.scriptasylum.com/rc_speed/_top_speed.html

Enter the values according to your desired setup; model, voltage, motor kv etc, and it will spit out results based on what you input, its very simple to use.

For example, you want ~45mph on the emaxx 3905 (?) with 2x2s lipo(?), in which case:

Differential Ratio: 2.8461538461538462
Transmission Ratio: 1.8333333333333334
Other Ratio: 1
Spur Tooth Count: 65
Pinion Tooth Count: 24
Total Voltage: 14.8
Motor KV: 2200
Tire Diameter (inches): 5.9
Tire Ballooning (inches): 0
Motor Current Draw: 0
Motor coil Ω: 0.006
Spur/Pinion Ratio: 2.71 : 1
Total Ratio: 14.13194 : 1
Tire Circumference (inches): 18.54 inches (470.8 mm)
Total Motor Speed: 32560 RPM
Vehicle Speed: 40.44 mph (64.96 km/h)
Effective KV Value: 2200

That would be a solid and sensible setup, with room for adjustment.

Choosing decent lipos and tweaking the esc settings will make all the difference for good temps, long runtime and best performance.