SO, my questions are:
(1) When towing, is it easier on your vehicle if you have manual transmission or automatic?
Auto trannys have become a very good at power transfer so there is very little difference. I still prefer a manual as I’m an old guy who learned with one.
(2) What causes the decrease in mpg when you are towing? Is it the actual amount of weight on the trailer? I would think that once inertia kicks in at steady highway speeds on flat roads, the trailer would be irrelevant (but apparently NOT).
(3) Or is it the windage (drag) of the trailer and boats that brings down the mpg?
It’s a combination of the two. Inertia will be overcome by drag and wheel friction.
(4) Or does it have something to do with the size of the trailer wheels vis-a-vis the size of the vehicle wheels?
There’s a number of things to consider when looking at wheels. The larger the wheel diameter, the more energy to get it spinning. There’s also bearing and road friction. One thing that would reduce drag would be to make the tire and rim narrower but the trade off would be weight capacity.
