Best Diesel SUV Tow Vehicles?

horton333 wrote:
4x4ord - your two posts contradict each other, the SUV has a 7 speed transmission so the chance of the trivial advantage you outline that may happen is just not there in this case.
Lower gears are not a "minor" advantage, the major advantage is why they go to all that trouble of having transmissions.

The point I was trying to make in the second post is that gear ratios are important at the time of engineering, however, us RVers getting picky about gear ratios isn't really justified.

After considering the general use of a vehicle, engineers will design the power train. In the case of a towing vehicle, mating the torque curve of the engine to the gear ratios of the transmission and final drive is very important. So for instance, the F450, with its 4.30 rear end, is designed to run at about 1760 rpm at 60 mph in high gear. The truck is expected to be able to travel on level ground at 60 mph and seldom need more power than what is available at 1760 rpm. When it gets working a bit it can drop a gear and deliver a little more power to the wheels as the engine revs to 2260 rpm. As it comes to a hill it pulls down a bit more and the engine begins to slow down. It will drop to 4th gear and rev to 2800 rpm where 100% of its power is being transferred through forth gear, the most efficient gear ratio, and the truck is traveling 56mph. An F350 dually is equipped with 4.10 rear gears (or optionally 3.73) anticipating that it will be used for a little lighter loads. So it would be cruising 60 mph at 1680 rpm where it makes a little less power and gets a little better fuel economy. When it gets put to work it follows the same gear dropping program and ends up being able to deliver its greatest level of power to the rear wheels in 4th gear at 2800 rpm where the truck is traveling 59 mph. Now if the these two trucks are put in a race up a hill it will depend on the slope of the hill and the weight of the trailers which one is going to have the advantage. Obviously if the combination of slope and weight are such that the F350 is running pedal to the medal in 4th gear at 2800 rpm it will be able to out do the F450 with the little higher ratio rear end. A different load or different hill and the results might be different. So now for us, who don't know the torque curve of the engine or the exact weights we will be towing or the % slope hills we will be going up, to think that we can out guess the engineer is a little foolish. The GM engineers basically said lets not complicate things and they use the same 3.73 rear gears behind the Duramax regardless of whether they are building a 3500 dually or a 2500...and it seems like the Duramax is often the first one to the top of the hill.