Cruise Control on Long Trips-My first sub 50 MPG Tank

I didn't make myself clear. When I say 1 car length, I meant traveling on a freeway, 1 car + 1 seconds of following distance not literally a car length of 15'. no sane person would drive bumper to bumper at 65mph. Hell, even the crazy ones would allow at least 10' of distance.

Anytime you're following a vehicle resulted in a reduction of drag, you're drafting, even if you're 1000 feet behind the vehicle in front of you.

When a big rig travels at 65mph it creates a vacuum behind it. Initially that vacuum will be great but will slowly dissipate and regain its normal atmospheric pressure of about 14.7psi. Think of a boat making a wake and that wake slowly calms. If you drive in the path of that vacuum you're reducing the drag of your vehicle. You are drafting and increasing your mileage.

Maybe I shouldn't use mythbusters as an example as they're did it at unsafe distances.

Back to the Prius's radar cruise control. The DRCC's 3 bar distance has about 3.5 seconds between you and the car in front of you. At 65mph that's roughly about 334'. Are you telling me that 334 feet space between me and the truck in front of me is unsafe? If 334' is unsafe then what is a safe distance? 500 feet? 1000 feet? 1/4 mile?

Since I got my Prius and started using the radar cruise control on the freeway, I've been paying more attention to the following distances of my Prius and other cars. I can tell you that EVERYONE on the road follows the car in front of them closer than me unless they're the lead car. Even all the cops and all the big rigs follow closer than me. I often get other people cut into my lane.

 

Agreed. Although I respect their bombastic pseudo-scientific approach to busting myths, I think that the drafting myth is only "plausible" in my book---provided that you're an idiot, and you're willing to close to within something close to the 0.5 seconds of separation I mentioned earlier.
Anybody who has ever ridden a motorcycle behind a large truck knows that the air is really dirty (roiled) behind the truck until you close to a certain distance---then you're "drafting".
Although it might be beneficial at some level to see some of these people edited out of the gene pool in a car-versus-semi tragedy, professional drivers usually work for companies (or pay insurance premiums for companies) that do not reward them for getting into accidents---regardless of fault.
My company (AT&T) is one of these. If some low-octane type plows intio me, I get a black mark in my record at the very least---and it's not atypical for an employee in my beloved company to get an unpaid vacation for a no-fault accident. Same with the military. At the beginning of every military convoy, there's always a driver-safety brief that ALWAYS begins with the statement "GOOD drivers do NOT get into accidents!"
Thus MY life experiences give something of a special loathing for tailgaters...and as I said earlier I now drive a Prius too, so you'll have to excuse me if I also have ill feelings for some of the "ambassadors" of my new association.

Drive safe! THEN drive efficiently!

 

Although the air behind the semi is quite turbulent when you're drafting at a safe distance, it is more moving with you than against you, so you will undoubtedly save fuel. I have no problem with people doing it at a safe distance - and most people don't try it at an unsafe distance, that I've seen anyway.

My brother used to be a semi truck driver; I've never heard him complain about people drafting him, but he gets really riled up about the people who pull right in front of him and then slow down - people are rather careless about putting themselves in the way of 80,000 pounds of hurt.

 

The last time I was on the interstate, I closed to within about 3 seconds of a truck and followed him(her) for 20-miles. Let me add quickly that I did this during the daytime. If you're 3 seconds behind a truck at night, you're still outside his(her) mirrors meaning they can still see you, but sometimes they don't like the resulting glare from your headlights for miles and miles at a time..
No sweat from a safety standpoint all things considered, but my mileage didn't improve measurably either. That's the point I'm trying to make. If you're "drafting" off of a big-rig there's a good chance that you might be a little too close for safety...otherwise you're probably not saving enough dead dinosaurs to bother with it.
Now this was a decidedly non-scientific test, with a limited data set, and I've only bothered to do it once. I'm sure some hypermilier out there has killed half an acre's worth of trees in computer printouts that prove me wrong---and I can save you a lot of printer wear by saying that I'm wrong all the time...

Peace.

 

I quite agree:

That is why I use slower moving trucks as a 'pacing vehicle' not for drafting because I'm too far back for any significant effect. Rather, the slower moving truck will be seen by following traffic that will smoothly move to the left lane and pass both of us rather than riding on my rear bumper.

Using a truck as a pacing vehicle means I can maintain 'truck speeds' which are much more efficient than normal car and SUV speeds on the Interstate without tailgaters. This is especially useful considering the ~65 mph 'knee in the curve' of my 2003 Prius and ~70 mph knee for my wife's 2010 Prius.

Bob Wilson

 

My 33K average in my Gen II is just under 54 mpg. 1000 mile round trip Denver, CO to 90 miles southeast of Wichita, KS (not many hills) and back at 70 mph= 44 mpg. It wasn't speed. At least on the Gen II, it was the combination of the Great Plains wind at 20-30 mph blowing from the southeast on my way to KS and blowing from the northwest on the return trip. And the cruise control. Even though there aren't many hills, that cruise control is just too good- at least after my 1990 and 2001 GM vehicles' cruise control systems. I've never had cruise control that worked so hard. I had to remind myself that 44 mpg was twice what my Blazer ever got on that trip.

Then last summer, I took it on a 200 mile round trip to Fall River Pass in Rocky Mtn Natl Park. No cruise control. No wind to speak of. 70 mph on the interstate part on average- probably 65 going up hills and 75 going down. Lots of curves so a probably half at 15-35 mph. Still got 55 mpg (probably about 33 going up and 77 coming down!).

 

All gen III Priuses have altered beam lenses. The beams don't have glares, especially 3 seconds back and at big rig driver's eye level. I do notice a 2-6mpg improvement when following a big rig 3 seconds back.

 

This makes more sense than anything I've heard in a while, and the next time I have to do the office-to-office thing on the interstate I'll give it a try...WELL outside the 3-seconds of course...

 

Returned last Saturday to Halifax, Nova Scotia from a week at the Hotel Frontenac in beautiful Quebec City. Sounds like we're getting about the same results:

2083.6 km total
total fuel burned 108.3 litres
total fuel cost CAN $112.67
calculated fuel usage converted 49 mpg (US)
tire pressure 40psi front 40psi rear
vehicle heavily laden and driven in hilly windy conditions, mostly at 110 km/hr with heat and cruise "on" (half the distance in rain)

BTW, the Frontenac offers hybrids free inside parking, a saving of $150 during our stay, which paid for my fuel and a very nice bottle of wine. Also, Quebec has some of the finest restaurants I've experienced anywhere in North America.

 

Hi Bob,

I am always impressed with the detailed graphs that you post here. If i want to do something similar, what do i need to do? I mean, is there any special software that you use and how do you collect such detailed information.