That will depend on many factors:
- motor
- battery
- esc settings
- existing setup
- surface
- layout
- etc etc etc
I geared my Reedy Mach2 at 3.88 with 38' timing on a tighter 36' x 60' carpet track.
I geared that same motor at 2.8 with 40' timing on a flowing asphalt track with a +200' backstretch.