So, I'm driving my new '09 Diesel RB across the country with nothing better to do than pay attention to the milage during highway conditions. Here are surprising results:
1. If you "go it alone" and run at about 70-75 you can expect about 16.5 mpg give or take.
2. If you slow it down to 65, you get a nice bump to about 18 mpg.
3. Here's the big surprise for me, slip in behind a big rig running about 70 mph and it jumps to about 20 mpg! That's a solid 15% gain. Not bad for a full-sized vehicle.
A couple of observations:
1. Safety tip: Part of my surprise was that I don't need to be as close as I thought to realize the benefit. I've been hanging out about three van lengths back.
2. Safety tip: Three van lengths back is not the time to be distracted by, oh I don't know, answering the phone, texting, screaming kids, that deep conversation your wife wants to have (I'm just say'n). Three van lengths back is a good place to focus on staying three van lengths back vice three feet into if you get my point.
I actually took the time to thank one of the truckers at a truck stop. He said he didn't mind at all and thought I was leaving him plenty of buffer.
3. Longevity: Besides the obvious fuel savings I gotta think it implies the engine and transmission are not working as hard either. That can only be good over the long haul.
4. Aerodynamics: I can tell you that as you double your airspeed, your parasite drag quadruples (mathematically speaking). My results (and common sense) suggest that the van is much higher on drag than the average car. Add to that going shopping at Aluminess and the drag likely becomes extremely significant. I'm guessing that means an even larger percentage gain from "drafting" with a "completed" van.
No surprise, I'm planning a long road trip once the van is finished at Sportsmobile. I will report back on any noticeable changes post 4x4 conversion.