Well, I started gliding in my 4wd pickup last night...
I visited my parents yesterday for Father's day and I decided to see what I can do gliding in my full size 4wd V8 pickup truck. Once I got to Mom & Dad's I filled my tank. I also topped off my tank at the station down the street from my home so I knew how much fuel was used on that trip. I did my best on my way home to glide as much as I can. I found out that gliding isn't as easy as it sounds. Its also easier to glide on neighborhood streets than on the highway. I need a much steeper grade at highway speeds than I do at 25 mph to glide. I guess its because a 4wd pickup is about as aerodynamic as a cinderblock. I noticed on slight grades on the highway I would loose speed if I shifted into Neutral. By the time I got home I think I have perfected my technique.
On the highway I kept my cruise set at 60. Under normal conditions that keeps my RPM's at about 1,500 on the highway. When I encountered a hill of great enough magnitude that I would not loose speed when I shifted into N I would tap my brake lightly to disengauge the cruise and shift into N in one smooth motion. My RPM's would drop to about 700 or 800. If I gained speed going downhill that was no problem as I was already going 5 under the limit. At the bottom of the hill I would shift back into drive, and once the tranny engauged I would give slight pressure on the accelerator before hitting resume. I found if I didn't do this the cruise would initially suck the pedal down real fast until it realized what was going on. This caused my RPM's to briefly kick up to about 2,500 for a second or two. I would let the cruise take me back up the next hill. This seemed to work well, and for a first time gliding experiment it got me 23.9 mpg, and under normal daily driving I usually get only 14 or 15 mpg. That's a gain of almost 10 mpg. I'm sure I can do better next time. I was so concerned with practicing gliding that I did not draft at all. I usually try to draft on the highway. I've obtained as high as 30 mpg in the truck drafting on long trips.
I think I also encountered another fellow hypermiler last night. It was a teal blue minivan - a Toyota I think. It stayed about 3 car lengths behind me for about 10 miles. If you read this I was in a gold full size pickup with a camper shell on I-95 North around Dumfries in Virginia last night.
What is the pressure in your tires? In my truck I get some pretty decent glides, though of course not as good as in my little VW.
I've kept my 265/75/R16 tires at 45 psi since they were new, and they have worn evenly. As I mentioned in another thread this is slightly taller and wider than the stock size from the factory. I will go back to the stock tire size later this summer when I buy new tires to reduce rolling resistance.