For the road 11 - 28 , for the hills 11 - 32 as you can´t have too low a gear riding the dirt and the 32 will allow you to keep a cadence at times where a 28 willl get you wheel spin , but most important : remember to oil your chain , frequently .If it´s sandy then use a dry lube but lubricate because a worn chain kills everything ,so get it checked frequently or buy a wear guage yourself .