215's are stock for your 2wd dually because the outset of the rims will not be enough and the 235's will likely rub together when loaded up.this could lead to blow out,which also takes out them stock pricey dually flares fyi.
however rear spacers can be purchased to provide more space between the rims,so 235's can be safely installed.
there are also more advantages to keeping the stock 215's.
the more tire width=the less the traction.
the more tire width=the more rolling resistance and wind drag (lower fuel economy.)
the smaller the tire= the less weight the tire weighs (less force the engine needs to use just to get your truck going.)
the 215's are shorter than 235's.
there are advantages to shorter tires as well.
the lower the truck sits,the easier it is to load up by hand.
the lower the truck sits,the less wind resistance there is.
the shorter the tire,the lower the effective gear ratio which is commonly thought of as "off the line" grunt only,which is simply not true,but the torque is multiplied through the entire power band,and why lower gears are performance gears,and taller gears are economy/cruising gears.
tire size is very important actually,and because we all use our trucks so differently no one can tell you which size will fit your needs better than you can.
good luck!
