Tires: 2006 F150 Tire size, worn tires, tire failure

Question
My 2006 F150LT Extended cab came equipped with P235/70/R17 108S tires. Recently a dealer installed 245 65 17 Uniroyals.  My gas mileage changed by 5mpg.  I am saying the new tires are the wrong size and he should replace them with the tires I first ordered.

Answer
Carolyn,

First, if your argument is based on the fuel economy, then you should be aware of 2 things:

1)  All other things being equal, worn tires get better fuel economy than new tires.

2)  OE (Original Equipment) tires are generally better for fuel economy than replacement market tires - although, replacement market tires are generally better for wear and traction.

So just the act of changing to new tires could completely account for the change in fuel economy.

But the OE tires were Extra Load type tires with a 108 Load Index and he replaced them with 105 Load index - and that direction is more risky for a load related tire failure.  The proper size in a Standard Load would have been P255/65R17!