gearing

[rcsammy]

hey everyone, hopefully someone can help
i ran a feigao 9L in my slash on 3S and 13/40 mod1 gearing and it was perfect but i have now converted my slash to a rustler and im running badlands which are larger than stock tyres
do you think i will need t change the gearing for the rustler? and if so by how many teeth? im unsure of what change i should expect, and i dont want to just buy loads of pinions without a rough idea of what size i will need