I have a Honda Odyssey (minivan, with automatic transmission). It gets 29-30 mpg on the highway with no trailer.
Every year I end up pulling a trailer loaded with boats from Key Largo to Ohio, over the mountains. With two Hobie Waves double-stacked (and a couple sets of beach wheels) the mileage goes down to about 23 mpg.
SO, my questions are:
(1) When towing, is it easier on your vehicle if you have manual transmission or automatic?
Depends on the car. If it is underpowered for the load and constantly changing between the top two gears, a manual in 2nd top gear is probably the go. Holding an auto in 2nd top and making sure it has a cooler attached should be fine but don't run it at top speed for hours on end.
(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?
Whilst you are accelerating most you are fighting the weight at lower speeds and a combination as it increases. When you are cruising, it's mostly windage that is the problem. You are in effect driving with a big parachute out the back of your car.
(4) Or does it have something to do with the size of the trailer wheels vis-a-vis the size of the vehicle wheels?
Not with regard to MPG. I do like the idea of larger trailer wheels though. A 15" wheel will do far less RPM than a 11" wheel and thus your wheel bearings and tyres etc etc will give far less trouble.
Tiger Mike
