What Pinion on a Brushless?

[Markoxx4]

Hi Guys,
Just putting my new LRP Vector x11 motor in a losi xx4 and wondering which pinion to use as it is apparently different with brushless.
it is the 6.5turn motor and i have the purple spur gear on(84 i think)
it says in the instructions it needs between 13.5:1 and 12.5:1 ratio depending on grip.
now im new to racing and it is all gibberish to me so please can any one help and how do you work it out so i know in the future!!
cheers guys.
Mark

[Oscar]

Id go for 14 or 15 teeth.

14 is 13.80 :1
15 is 12.88 :1

[Markoxx4]

Thanks, ill give that ago.