Does anyone know why the 4X4 trucks use a larger/taller tire the a 2X4 truck with the same options(engine & gear ratio)? My truck has 245 70 R17 and I'm debating going to the larger 4X4 size tire, for a variety of reasons, availability, cost (larger tire is more common) and the small tire looks lost in the wheel opening.

I always thought it was odd, because a 4X4 would have the extra drivetrain to rotate and would benefit from the extra torque of a smaller diameter tire.

 

The higher tire profile gives the differential higher ground clearance.

The larger tires cope better with the off-road and heavy duty on road use to which a 4X4 is subjected to. A larger air cushion gives a better ride under harsh conditions.(In theory.)

Some of those larger tires, especially on the HD models, are also "E"- rated, 10ply,80PSI. Your basic tractor trailer radial construction. R-R-R!