I have never drifted but for sportsman class I would probably stay in the 4-5fdr (final drive ratio) range for a 17.5. I would also highly suggest a motor fan and maybe an esc fan as well. So stock 72t 48p spur with a 45t pinion would be 4fdr and a 36t would be a 5fdr so any pinions between them would be in the range. Figure the fdr by dividing the spur by the pinion and times by 2.5 for a TC3. You can dremel out the webbing under the pinion to run larger gears. If you have no gears and need to buy them you may want to start with 64p gears as the options are wider.