[dadgummit]

I too just started converting a crt.5 and I am using 1/10th scale truck tires. In my opinion they look better, will last longer and have a flat patch of rubber on the road (as opposed to the rounded buggy tires that come stock) and they are about 4" high which allows you to run a smaller pinion gear. here is the speed calc with a 2s pack and a 3600 kv neu motor:
Differential Ratio: 3.25
Transmission Ratio: 1
Other Ratio: 1
Spur Tooth Count: 46
Pinion Tooth Count: 16
Total Voltage: 7.4
Motor KV: 3600
Tire Diameter (inches): 4
Tire Ballooning (inches): 0
Motor Current Draw: 0
Motor coil Ω: 0
Spur/Pinion Ratio: 2.88 : 1
Total Ratio: 9.34375 : 1
Tire Circumference (inches): 12.57 inches (319.19mm)
Total Motor Speed: 26640 RPM
Vehicle Speed: 33.93 MPH (54.5km/h)
Effective Speed Rate: 4.58mph/V (7.36kmh/V)
Effective KV Value: 3600