pulley problems

I have a tamiya ta06 and I saw the thread posted here about what tooth to go with, my question is I'm goin with a 13/20 do they both have to be one way pulleys or does it matter. I was just curious before I buy them.  

Ta06 comes with tamiya mod pitch spur/pinion. They are designed for strength so that novice userswill not constantly strip them. I would recommend buying 48p spur/pinions. depending on your motor/esc setup, i'd say a good baseline spur is 88t 48p and pinion anywhere from 19-25t 48p

Sorry I was asking about the 2 pulleys that connect to the diff. The front diff is a 39t connecting to a 13t and the rear diff is a 40 or 39 I can't remember now connecting to a 20t. So I was curious does the 13t and 20t pulleys have to be one way bearings or can they be normal pulleys? But thank you for the info on the pinion/spur gears that was actually gonna be my next question when I pick up the esc and motor.