http://www.petitrc.com/setup/durango..._GearChart.pdf
http://durangofansite.com/gearing.html
it works out about a 29/30/31 but you can't get anything more than at max a 26 in there. You will have to look at getting a smaller spur, about a 78-81 ish then a 25-30 will fit, or look at getting a quicker motor depending on the esc you have