Tires: Oversized Tires

Question
I have a 2009 Chevy 2500 Express van with a duramax diesel that calls for LT 245/75 16 tires.  I would like to go to a LT 265/75 16.  I understand this will alter speedometer readings slightly but are you aware of any other potetial problems going to this size on this vehicle?  Also, how will this affect fuel economy?

Answer
Ricky,

According to Tire Guides, the wheels on your truck are 6.5" wide - and an LT265/75R16 requires a minimum of a 7" rim. Using a rim that is too narrow may make the vehicle track the grooves and ruts in the road, plus make it sensitive to cross winds.

Fuel economy?  Tire size doesn't play much of a role in fuel economy - other than make the engine turn slower.  That sort of thing has been proven to help, but the reduced torque sometimes causes people to press harder on the accelerator and negate the improvement.