F/R gear ratio for 1/8 on-road conversion

[BrianG]

Well, that depends on the top speed you want to hit. Plug some numbers into the calc and see what you get (parameter solver may help more here).

Just keep in mind any gearing limits (motor size, motor mount adjustment, etc), and allow room for further tweaks (in other words, don't get a ratio that will put you at the upper/lower limit of spur/pinion choices).