Highway MPGs Using DRCC: 63.4 at 60+ mph

Discussion in 'Gen 3 Prius Fuel Economy' started by a priori, Sep 25, 2009.

  1. a priori

    a priori Canonus Curiosus

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    Before you get all upset, remember that I've only reported on 3.5 hour stint. I made only one stop, and the car already was warmed up when I started this measuring. In many peoples' books (including my own, really), this is only a brief glimpse of what mileage can be like on the highway. It is long-term driving that really shows what to expect for mileage.

    Look to my signature to see my real mileage over time.

    I just wanted to show that long drives at real highway speeds can produce good mileage. I also wanted to show that the DRCC appears to have a positive effect on mileage. (It also is a much less stressful drive, because you don't have to start and stop the cruise control or even worry about managing the approach to slower cars.)
     
  2. a priori

    a priori Canonus Curiosus

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    I don't disagree with hobbit about his safety concerns. I got a bit prickly about his statements that I felt were unfairly criticizing certain assumed driving habits.

    I'm certain hobbit wouldn't have posted his views if he wasn't actually concerned about not only my safety, but also the safety of other readers who might try to replicate my DRCC experience.

    I would say the only time I felt I could have been a bit too close is when we were in very rural areas, and there were no other car or truck around. Still, it was so much simplier and easier to continue driving on and to keeping paying attention to what was happening infront of me!
     
  3. kaptmorgan

    kaptmorgan Junior Member

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    I would never park behind a truck and destroy my paint job and if the truck was to slam on his brakes and something was to go wrong that cattle cutter on the lower rear bumper would make short work of his car. I don't think any sane person going out and try this! But its great reading.
     
  4. Celtic Blue

    Celtic Blue New Member

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    Thanks for that, unfortunately it BEARS ABSOLUTELY NO RESEMBLANCE TO WHAT WAS BEING DISCUSSED. So while it is an interesting strawman it missed the point entirely. Do you have any clue as to the distance being discussed in real life terms? I'll bet that you routinely follow well within the range you "don't think any sane person" would be wthin.
     
  5. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

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    agreed. 150 feet is nearly 8 car lengths. when i took drivers ed back in the stone age, i was taught one car length per 10 mph which is something i strive for frequently achieve rarely
     
  6. ALS

    ALS Active Member

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    The seventeen inch wheels and tires run 11 lbs heavier.

    At speed there isn't much effect on fuel economy between 15" and 17" wheels. The fuel economy hit is during acceleration when more energy is needed to spin them up to speed. The other down side to
    the 17 inch wheels and higher unsprung weight is handling on uneven pavement. They will take longer to respond to rough pavement. In other words you will get a lot more wheel hop.

    In looking around for additional information the 17" combo over the stock 15" wheel and tires is worth a loss of around 1.75-2 mpg.
     
  7. hobbit

    hobbit Senior Member

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    Y'know, I get this "counterargument" about how all these extra
    cars are going to jump into a generous gap all the time, and yet
    never see it in reality. First off, if you and some traffic
    ahead are tooling along steady-state minding your own business
    and someone comes up to pass and clearly wants to go faster,
    why would they jump into that gap and then just have to jump
    right out again when they come up behind the traffic farther
    ahead? Well, maybe because they're not paying attention far enough
    ahead, that sometimes does happen ... but they're already going
    faster than you, and thus generally don't affect your own travel
    speed. If they're cutting in [for whatever reason] and then
    *slowing down*, you're not leaving a big enough gap. Generally
    you want to have enough space for other people to get in, get out,
    do their routing/offramp or whatever they need and be on their way,
    and they don't affect you at all unless you've positioned yourself
    in a way that actually impedes their ability/safety to do so.
    .
    I'm really trying to envision a truck, a Prius a nice safe five
    or so seconds behind, and ten other overtaking drivers with a burning
    need to all pile into that space too. Sorry, it just doesn't happen
    that way. Not even in the infamous high-density "directed malice"
    type of Boston traffic I mix it up with on a regular basis.
    .
    What I consider proper following distance is pretty long but gets
    me there at the same rate [since I'm still tracking the same speed
    traffic, just farther away] and gives me plenty of time to see where
    the thrown alligator is going to flop and land and gently swerve
    around it. Yes, it's happened. If I was in DRCC la-la-land right
    then I'd probably have a different car at this point. Not to
    mention the gravel trucks raining little rocks out the back gate,
    all of which finish bouncing and land safely on the road before
    I reach them. See the seminal article on this for more benefits.
    If you haven't gotten the point by now, I give up.
    .
    Can someone actually generate a nice little table of the SECONDS of
    following distance that DRCC actually provides in real life at
    differents speeds and the different distance settings? That would be
    an interesting chart to have. No, you can't do it by car lengths;
    no driving school worth its salt teaches it that way anymore. There
    is a dilation factor that happens at higher speeds that the old
    saw doesn't take into account. Watch something ahead pass a fixed
    point and count seconds until you pass it, etc etc.
    .
    _H*
     
  8. a priori

    a priori Canonus Curiosus

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    I'm not picking any argument with you. I'm just reporting what is happening to me. This isn't a question of some hypothetical event. I'm following traffic in one lane and there were two ways this happened on my last trip. One: my lane is going faster than the right lane and we come up to someone just waiting for a chance to move ahead of the slower traffic. Two: my lane is going about the same speed as the other lane, and a driver comes up in the other lane and thinks by jumping to my lane it will be an improvement. Perhaps you don't see it because you are more than 5 seconds behind.

    OK. So the essence of it is that you don't believe the use of cruise control is a good idea. You think a 5-second following time is necessary for safety. That's fine. But why tell me I'm not paying attention and am in "la-la-land" when I drive? And when am I going to choose to drive behind a truck that keeps throwing junk down on me?
     
  9. Celtic Blue

    Celtic Blue New Member

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    Hobbit,

    No place in the U.S. I've ever lived behaves the way you describe. None. I've seen plenty of people making the very sort of idiot maneuvers in front of my Prius that you claim do not happen. (Hell, the car seems to attract those sorts of nice person clowns because they think the Prius driver will move like a snail.)

    You assumed an inattentive driver. That was a mischaracterization.

    The worst drivers on the road are often the slowest and they cause all sorts of mayhem, often driving cluelessly side-by-side with some other slow vehicle(s) creating what I term "the mucous plug." They usually aren't paying attention, many shouldn't have a license and they create all sorts of bottlenecks. I see these kind of jackasses all the time reducing the carrying capacity of a road. I notice them more in the Prius because they are the morons riding their brakes at the bottom of the hill, creating the standing wave behind them. They aren't the ones clearing the wave, they are the ones causing it. Doesn't matter that I'm holding way back at two, three or more times the following distance of the other traffic (common for me in the Prius), they still force me to dump my energy because they can't drive for squat. Could be that I'm sensitive because I had to brake for one that I was ~10 seconds behind at the start of a hill today. The same putzes slow down for entrance ramps...as if entering a 65 mph zone with a 20 mph delta V (as in 45 mph) is somehow safer than merging at similar speeds to the prevailing traffic. Watched a fire station commander in his station truck do this the other day...wondered if he was trying to drum up business as I rode the Prius brakes down the hill of the entrance ramp.

    My rule of driving is simple: if I'm driving well, nobody should have to brake, cut their cruise, or swerve for me. If they do, then I'm probably an impediment to traffic flow. Doesn't matter if I'm driving a Prius, a sports car, 4x4 or commercial truck. I remain situationally aware and try not to impede traffic.

    If folks drive with a 5 second following distance we will need a lot more roads, because that is nearly 3 times the choke flow. (And choke flow would be even higher if the average U.S. driver were more attentive.) Time to turn 8 lane roads into 24 lane roads. And I've lived in a number of places that regularly acheive choke flow. You can't evacuate them during a hurricane (see Houston.)
     
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  10. Indyking

    Indyking Happy Hyundai owner...

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    Interesting experiment and results, BUT (there we go) I do question your perception about the MPH. The MPH is recorded whenever the car is "on" I believe. So, if your MPH was 58, it does not matter if you were driving 65ish most of the time because those short periods of time (constructions or slowing down) caused your MPH to go down and therefore improved your overall MPG significantly (so, simply stating, your MPH was 58, not 65!). To really test the ability of the DRCC in improving your MPG in the hwy, you should have recorded the MPG in a separate trip log, setting it on when chasing the trucks in the hwy and recording the number mentally before bringing the car to slower speeds (for a reasonable distance), in other words, getting a real 65 MPH on average!

    Speed does have a huge impact in the hwy MPG for the Prius. In my first trip to WI, (400-500lb of cargo, temp on the 60’s, light rain in the first 1/3 of the trip, calm winds, 360 miles total), I was averaging 65-67 MPG when leaving Indy through slow-speed highways (average speed of about 55 MPH) under rain, then my MPG crept down to 54-55 once I moved to a higher speed hwy and kept the MPH around 75 (much less rain at that stage). Was my MPG really 54-55 driving steady at 75 MPH with the car loaded? Of course not, it was more like 50ish (perhaps even less) but the short, yet very significant slow start with 65-67 MPG helped to keep the final number above 54! So, I was still satisfied with the final MPG. If the car keeps getting above 50 MPG for the entire trip throughout winter, I will be very happy!

    By the way... my tire pressure? 38/36 psi, so not that much different from the recommended 35/33... I see people are getting improved MPGs with 45+ psi, which I'm afraid I will never try because if I hit a pothole in high speeds with a heavy car and that much pressure in my tires... I don't like to take that risk... besides; handling/comfort may be a bit compromised with that much pressure.
     
  11. a priori

    a priori Canonus Curiosus

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    Perhaps I should've been clearer, here. Yes, I understand the MPGs were helped by the slowdowns during construction, but they also were hurt by the speed up, after construction. The real damage to the FE was the stops. The particular hit is when sitting with the car on, going nowhere for 10 minutes. THAT will do a number on your mph figure!


    Well done!

    One of the times you SHOULD be increasing tire pressure is when you are carrying a heavy load. If you hit a pothole with a heavy low and lower pressure, you risk damage to the wheel. Damage to the tire is much less costly!

    You could bump up the pressure for those longer trips and then reduce it when you are tooling around town alone.
     
  12. a priori

    a priori Canonus Curiosus

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    I've completed the round trip, and I've done my calculations!

    I think I'll start a Part 2 (or Part Deux) for further discussion. (I tried this last night and when the connection was lost I lost the whole page. No, I didn't create it separately and copy it over. I only do that on long pages when there will NOT be a connection loss.)

    Short: My return trip covered slightly different ground (so I could drive faster), and I did it early in the morning and with few trucks to guide my way. I ended up with a MUCH higher mph and a lower MPG. Still, the overall return trip showed surprisingly high mileage!
     
  13. Celtic Blue

    Celtic Blue New Member

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    That's not even the main reason to run with more pressure when you have a full load. The sidewall will have to flex and stretch more with each rotation at lower pressure. This results in dangerous heat build up in the tire that can lead to catastrophic tire failure.
     
  14. a priori

    a priori Canonus Curiosus

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    OK. And the poster was interested in avoiding problems hitting pot holes, so I provided a response along those lines.
     
  15. Indyking

    Indyking Happy Hyundai owner...

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    I see... fair enough!




    Kudos for the Prius... not me... I just set the CC at 5-10 above speed limit and let it go... HSD did the rest :D


    I guess it makes sense, but just from my physics 101, if the tire pressure is too high, increased weight bearing will increase the chances of blowing up when hitting a pothole or object...

    My concern is not really the cost of wheel vs. tire… a blown tire in high speeds can be very dangerous whereas a damaged wheel will give you some time to stop and replace it. ;)
     
  16. Indyking

    Indyking Happy Hyundai owner...

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    Which proves my point raised earlier... :D:D:D
     
  17. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

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    tires are not like balloons. putting additional pressure in them DOES NOT increase the likelihood of a blow out if hitting a pothole.

    the only issues of over-inflation usually does not even begin to happen until you are significantly above max tire pressure. this is where crowning starts which means less road contact, less control, greater stopping distance. even at these pressures, blow-outs are still not an issue

    for under-inflation, greater tire wear, sidewall damage, AND BLOW OUTS are more common...

    if you want an analogy, look at an above ground pool. notice the difference in stability when the pool has 3 inches of water in it as compared to 3 feet of water in it. with less water in it, the sides are easy to distort and collapse. the additional water helps stabilize the pool. the tire is not much different
     
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  18. Indyking

    Indyking Happy Hyundai owner...

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    Except that rubber seems to be a lot more strong and solid compared to the plastic along the walls of a ground pool... ;)
     
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