[lincpimp]

That is the fun part. Usually the motor is rated with a max amp draw number. This is the number that I usually add 20% to and find a lipo that is similar to that figure. Not guaranteed, cause some motors can be geared to pull at or more than their max rating. Also if too high gearing is used it can create alot of heat in the motor and esc which can draw more amps from the battery. This is why it is good to gear low when testing a new setuo, and to use an already tested setup, like most of the guys here use. Saves time ad money using an "established" setup.