What size should I use
 

I recently bought the WLtoys 144001 and upgraded it with the 120A esc and BL3650 4300kv brushless motor. I’m having issues with hesitation going from 0-1mph. I read somewhere that resistance from the wheels to driveshaft will cause that however lack of power can also cause the problem. I’m currently using the original 7.4v 1500 mAh battery. Can anyone point me in the right direction?

Hesitation (cogging) is common in sensorless systems. They don't give the low speed control of a sensored system. Especially if they are a cheap system from a cheap brand.

I have the same issue as I usually buy the WL toys stuff to mess around since they're cheap. The previous responder about the cogging is accurate. The cogging is really bad with a brushless motor, especially the main spur gear is metal. I went back to a brushed 550 can and not much better.

Just to be clear ....
Cogging can be really bad with sensorless brushless motors - but generally not an issue with sensored brushless motors and ESCs.

Recalibrate ESC, if same thing drop pinion 4 teeth or more.. Good Luck!