Gear Ratio Chart/Pinion Gear Selection - Evader ST/BX With 87T Spur
Internal Gear Ratio 2.66
  Off-Road Tires Street Tires Foam Tires * Off-road calcs = Gladiator II tires w/ 4.25" diameter
Roll-out 13.352 10.996 9.425 * Street calcs = Street Hawg II tires w/ 3.5" diameter
* Foam calcs = Generic foam tires w/ 3.0" diameter
Final Drive Ratios
Pinion FDR (*:1) Pinion FDR (*:1)
15 15.428 21 11.020
16 14.464 22 10.519
17 13.613 23 10.062
18 12.857 24 9.643
19 12.180 25 9.257
20 11.571 26 8.901
Efficiency Ratio1
Pinion FDR:RO - Off-Road Pinion FDR:RO - Street Pinion FDR:RO - Foam
15 1.156 15 1.403 15 1.637
16 1.083 16 1.315 16 1.535
17 1.020 17 1.238 17 1.444
18 0.963 18 1.169 18 1.364
19 0.912 19 1.108 19 1.292
20 0.867 20 1.052 20 1.228
21 0.825 21 1.002 21 1.169
22 0.788 22 0.957 22 1.116
23 0.754 23 0.915 23 1.068
24 0.722 24 0.877 24 1.023
25 0.693 25 0.842 25 0.982
26 0.667 26 0.809 26 0.944
1 Ideal Efficiency Ratio is closest to 1:1.  Depending on the kV of your motor, you may need to gear up or down to find the sweet spot.
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