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Hi all,

So I've got an insane tank going (see my sig). :D I may be driving home for Easter though, and that means ~500 miles round trip of highway driving - secondary highways, I can stay off the interstate. I have no problem keeping it to 55 the whole way... but no matter what I do, I can't seem to manage better than 55MPG for the round trip. :( I've read Hobbit's write-ups on the "sweet spot", though I haven't had a big highway trip since then to put that into practical use.

I've seen elsewhere "65[MPG] at 55[MPH], 60 at 60, 55 at 65" but I haven't been close to that for any appreciable highway trip. I'd love to get 65 or better.

Here are some of my lines of thought about highway road-tripping. Note that they are mostly questions. :confused:

- DWL or "maintain-speed-up-hill-and-WS-down-the-other-side"?
- best way to ascend a 2-mile 5-6% grade?
- even at 55, if I try to maintain iFCD ~65 I'll slowly lose speed on level ground.
- drafting tradeoff - is the interstate better vs secondary highways at 55 if I can find a draft target at 70? 65? 60? (Keeping in mind that I'm not comfortable with anything closer than distant draft.)
- what's my steady-state iFCD target?
- can anything I'm seeing on the SG-II help?

Is there something big I'm missing? Other thoughts? Thanks in advance for any insight. :)

The drafting question is the only one I might be helpful on.

My experience is interstate truckers are less likely to discourage drafters than truckers on secondary highways. I tend to be about a car length away - closer than you like. At that distance, my biggest problem is missing exits, so I've set my GPS on maximum zoom to "see around" the truck. Even if you were 2-3 or even more car lengths behind, you would get benefit.

Well, if you could find a semi to ridge ride or distance draft at 55 MPH then that will easily give you the best results. If you do the same on the interstate you'd probably get about the same mileage as going 55MPH without the ridge riding and such.

Your steady-state iFCD shouldn't determine your speed. Your speed should determine your iFCD.

BTW, you may only be able to get 65MPG going 55 and ridge riding or distance drafting. You could also get 65MPG if you were on the interstate, but close-in drafting. It's our choice. You either get speed, MPG, but worry about hitting the brakes or you get MPG, no worries, but slower speed. Or your other alternative is to not worry about MPG, but I don't think that's what you want.

- DWL or "maintain-speed-up-hill-and-WS-down-the-other-side"?
- best way to ascend a 2-mile 5-6% grade?
- can anything I'm seeing on the SG-II help?


I think these questions are all related. Data and experience presented so far seems to indicate that the ICE efficiency is highest when it's kept in a band between 1500RPM and about 3,000RPM or a little less. (Bob Wilson has presented some interesting graphs at GH...I think they still need work but it's a good start.) You can use the SG to keep track of engine speed in real time, using that information to keep the engine within that band...when it's running. ;) Heading down any substantial hill is likely to put engine below that 1500RPM mark, so you are probably better off taking some warp-stealth time and pulsing to bring the speed back up if necessary. To me this means that you are better off maintaining speed up the face of the hill *if* that doesn't mean that the engine has to wind up too high. (That maximizes your odds of a good glide down the back side.) If RPMs creep up past 3k then I would start to DWL if traffic conditions will allow it.

DWL doesn't do much for very long grades, so you probably ought to shoot for whatever steady speed keeps ICE RPMs reasonable.

Long hills are a killer, there is not much you can do except slow down as much as you think is safe. I think the best plan is to use Tim's idea of using the scan gauge to watch RPM, but I think Wayne's advice would be to just maximize iFE as much as possible and (my advice here) on your way down hills use warp stealth if you are at 55 mph or more. At 55 mph in the summer on rolling hills between Maine and Massachusetts (interstate 95 mostly) I can get 60-62 mpg and at 62 mph I have managed 57 mpg on the same trip (I think my tires were at 52F/50R and the Integrities were getting thin, I was also running Mobil 1 0w20 about 3/8 inch below the full mark or about 3.25 quarts at the oil change).

Dennis

Mostly reinforcing what the others (including Hobbit in his papers) have said, here's what I do:

In short, when the ICE is needed, I keep RPM (monitored by ScanGauge) between 1500 and 2400, with 1700 as the (presumed) ideal. I use warp stealth when the ICE is not needed.

Keeping RPM in the target range allows me to maintain or slowly gain speed on level terrain or gentile uphills. I use warp stealth on downhills if I can maintain or gain speed with it. On gentle downhills where I lose speed with warp stealth, I may either use it anyway or run the ICE within the target range, depending on my speed and the length and incline of the upcoming segment. I allow momentum to build on the long or steep downhills, but staying safe and ticket-free, to help get over the next uphill.

If it's a busy highway or I could incite road rage, I set my cruise control for an absolute minimum as a "safety net." For example, a couple of weeks ago on I-95 in Virginia, speed limit 65, I had CC on 60. That serves a side benefit of giving my right foot a break from constantly working the pedal.

I may draft a truck (not close-in), but I've often found that trucks either are consistently too fast (75+) or vary their speed out of sync with my variations.

On that I-95 trip I got about 58 MPG, temps in the 30s to low 40s. I've gotten in the low 60s in warmer weather.

It's a shame you got a big highway trip on THIS particular tank. How important is Easter? :)

Elevation change seems to have a noticeable impact. I was able to do 120 miles on state highways with no drafting at 60mpg simply because of a 500 foot drop over those two hours. There may not be much of that where you are headed.

I also hopped on the interstate once and nestled in 1 car length behind the slowest Wal-Mart 18 wheeler you can imagine (50-55mph). It was like he was carrying me home. I had two bars around 66-68 on level ground. Those slow movers are like gold.

It's a shame you got a big highway trip on THIS particular tank. How important is Easter? :)

Heh. ;) It's still a "maybe" at this point, but I've been thinking the same thing. Just planning for the "worst". I haven't ruled out trying to find back roads the entire way either. :D

Thank you to all for the wealth of info posted so far. I've made the following mental notes...

- shoot for 1700RPM steady-state, though anything up to 2500 or so should also be fine
- don't worry so much about iFCD
- go between this steady-state and WS as dictated by terrain
- try to find that miracle target going 55 ;)

So if I'm a shallow drop where I could iFCD at ~75 or higher (but where the ICE would be under 1500RPM), it's more preferable to go between load and WS?

I also hopped on the interstate once and nestled in 1 car length behind the slowest Wal-Mart 18 wheeler you can imagine (50-55mph). It was like he was carrying me home. I had two bars around 66-68 on level ground. Those slow movers are like gold.

I agree they are like gold, and one of the best things to anchor yourself to. They act like a pacer car keeping your speed even, and take all the worry away of having anyone follow you too close. Nobody wants to get behind a slow moving parade like this. Any drafting effect you want to add is of course, gravy.

And if the wal-mart drivers are doing slower speeds by
corporate policy, they've obviously noticed that "spirited"
driving doesn't gain anything in terms of timely delivery
vs. all the risks/downsides of higher speeds...
.
It's nice to hear that all my blathering is returning
positive results for other people. I think I've been
through about three changes in thinking WRT highway MPG,
perhaps in a minor way, but it seems that everyone's
converging on the same fairly narrow range of optimal RPM
[from which power can be almost linearly mapped, because
torque is largely constant across it]. Now, all we need is
an easy and instantaneous way that everyone can determine
if they're in warp-stealth, since that's a bit more subtle
but carries additional benefits.
.
_H*

I recently did a ~900 mi round trip from Oakland to Joshua Tree NP. We drove my old truck, an 88 Nissan Pathfinder, V6 Auto, 4x4. This thing is normally a total gas hog, averaging about 15mpg in mixed driving. After trying some things with great success in my Toyota, I decided to try similar in the fire breathing dragon that is the Nissan..........
70 psi (truck tires that want 50 to begin with.....) and I slowed down and did the drafting thing as much as possible (I was quite surprised, it seems that there's ALWAYS a truck to draft on I-5). After a few years doing gigs all over the bay area, semi close drafting, 2-3 car lengths, seems like the normal following distance anyway.....
the result? 22.8 mpg for the tank, I made it home on just a hair over one tank (20 gal), instead of the one and a half it took to get there....

It seems to me that the interstate routes have the distinct advantage of more traffic and more drafting opportunities. The trucks don't seem to mind, they draft each other a lot anyway, and if you don't mind letting them shuffle (they take turns drafting) they don't seem to mind if you tag along at the back of the line. I think on this return trip I spent a grand total of about 30 minutes out of 9 hours not drafting someone, either an RV or a semi.

Does anyone have data or opinions about comparative route distances, penalties in mpg for increased number of stops necessary on state rts. vs. freeways, and the effect of things like hills and slower speed turns? It seems to me that freeways have distinct advantages for FE over secondary routes, especially if you drive a conventional car, and aren't stressed by being passed constantly by people who are in a perpetual big hurry.

Driving 55 on the freeway feels weird at first, and then it starts to seem dangerous and wasteful to go any faster. Sitting behind a truck really is like getting a ride, it takes so much stress off as a driver; now instead of trying to jockey for position with the fast laners, you can sit back, enjoy some music or a conversation, and when you arrive at your destination, you're not nearly so road-buzzed and fatigued, even though it took 2 hours longer to get there ;-);)

Yea, drafting helps a lot on the interstate. I'm not sure how you ended up going 55 MPH, even behind a semi. Over here in Atlanta even the truckers speed, like 65 MPH or more. I can draft them anyways, but if they go over 70 MPH I don't even bother since I end up losing MPG just trying to keep up at that speed.

It'd help a lot more if they just towed us the whole way, lol. It's not like the weight of towing our car would really affect their mileage that much. I doubt it would even change it .1 MPG, but it does make me wonder. At that rate it'd be better just to be towed by a semi than to drive on the highway, even in a Prius or Insight.

The most extreme example of improvement in drafting was done by a writer for Car and Driver. In Janurary 2000 he drove a Honda Insight very closely behind a Ford Explorer at an average of 58mph. Being so close as to be in virtual tow, they had phones in case the Explorer had to stop. The Explorer also had a block to afford even better drafting.

Normally in ideal spring weather, 70-80mpg at 58mpg is possible on a 5-speed Insight - he got 124mpg!

My experience in close drafting is 20-30% improvement.

Update - I will definitely be driving home next weekend. The tank will be about 70% done by then. I really don't want to hose my record tank. I might be able to do 60 highway but not 73. :( So, second question - what's a good way to find back roads with their associated speed limits? ;)

Hi Jared:

___Are you coming up from Chicago way as you could take the frontage roads from a little North of the Il./Wi. border all the way up to Milwaukee. From there, there are a lot of county roads to zig zag all the way home if you could stand it? It would take you forever but I bet an 80 + would be doable in 50 – 60 degree temps?

___My money is on Tim finding out a better method for an almost all highway Prius II commute in that he is pushing some interesting techniques for 60 + mph and is already flirting with 60 mpg segments in temps that are not quite what I would call hypermiling friendly. You have the cold-short-city capabilities locked down better then anyone on the planet at this point in time though :)

___Good Luck

___Wayne

You know, you could always fill up your tank before you do the driving next week.

You know, you could always fill up your tank before you do the driving next week.

:o That would be the easy route. :D My crazy idea is to somehow come up with 70+ anyway.

From there, there are a lot of county roads to zig zag all the way home if you could stand it? It would take you forever but I bet an 80 + would be doable in 50 – 60 degree temps?

That's the idea :cool: I'm going from Madison to about halfway between the twin cities and Rochester, MN.

Or maybe I should just suck it up and work on the "highway fu" even though I'll take a hit. ;)

As a rookie... I'm a bit confused about using a Scangauge to monitor RPMs. Why wouldn't one concern themselves with solely the immediate mpg readings? I'm about to receive my Scangauge II and want to make the best use of it of course.

Thanks,

Bob

Hi Bob:

___Welcome to CleanMPG! I hope you like what you have seen so far ;)

___I am not sure what type of automobile you are currently driving but the Prius’ don’t have a tach so it is useful for them to display that data point on the display at all times. For others, it depends on what is lacking or what makes the most sense. On the Accord and Ranger, I view the iFCD, Load, TPS, and Batt V as they make the most sense for my driving style. I do keep an eye peeled to the OEM tach’s as well however.

___I am somewhat of a purist given RPM’s and load are directly related to your iFCD depending on the conditions you are currently traversing. In fact, the iFCD is my main focus with the rest being more confirmatory then being used for feedback other then keeping within a broad band.

___Good Luck

___Wayne

The main reason that you would focus on RPMs in a Prius is that high readings on the FE readout don't necessarily mean an efficient state of operation. This comes into play in a situation such as descending a moderate hill, which could result in the ICE running at very low load, with very high numbers (perhaps even 99.9mpg). Most drivers would think "hey, this is great!" But the reality is that the engine doesn't convert gasoline to mechanical grunt efficiently at all when it's running in such a state, which is low RPM and most likely a closed throttle plate. The better choice would be to use your Scangauge or your tachometer to recognize this situation and transition to a different mode of operation. That would be feathering the accelerator to get into one of the glide modes, which is a zero-fuel state. If you can hold speed, great. If you can't, you can always alternate between the glide and a quick burst of power at a higher RPM, which corresponds to a higher energy efficiency. Your engine will have produced roughly the same amount of energy on the way down, but it will have used much less fuel to do it because it was only operated at that high level of efficiency.

Now that's mostly a Prius thing, and we also want to watch it to make sure that the RPMs don't creep to high if at all possible. It's also a special case. You probably would just watch the FE numbers while cruising down the level highway because it is less likely that you are going to be in a P&G mode (pulse and glide...alternating between efficient bursts of power and no-fuel glides). Unless you really want to, of course. ;)

I hope that makes sense.

Thanks Brick and Wayne... that helps a lot. I hope to get my scangauge tomorrow... I feel like a kid at xmas.

Bob

___Are you coming up from Chicago way as you could take the frontage roads from a little North of the Il./Wi. border all the way up to Milwaukee. From there, there are a lot of county roads to zig zag all the way home if you could stand it? It would take you forever but I bet an 80 + would be doable in 50 – 60 degree temps?

Microsoft Streets and Trips can help a lot in selecting a good hypermiling route if you use it right, and it's cheap. I found that if I was honest about my average preferred speeds on different road types (27 on streets, 42 on highways and 52 on expressways), it would come up with an honest quickest route to a destination -- the low highway/expressway differential will usually bias it toward highways, since they're more readily available.

I also frequently use it to find good cycling routes, and these routes would be optimum for hypermiling as well. To bias it away from the expressways, I'll type in speeds of 5 MPH for expressways/limited access roads, 20 MPH for everything else and ask for the quickest route. :)

One other suggestion...Aero mods will help the most with the higher speeds of expressway travel; the most helpful appears to be a grill block, followed closely by wheel skirts. I use the former but not the latter. Each is good for a few percent, which can mean a few MPG on a Prius.

Microsoft Streets and Trips can help a lot in selecting a good hypermiling route if you use it right, and it's cheap. I found that if I was honest about my average preferred speeds on different road types (27 on streets, 42 on highways and 52 on expressways), it would come up with an honest quickest route to a destination -- the low highway/expressway differential will usually bias it toward highways, since they're more readily available.

Hi Bruce,

I picked up the 2007 version if only to have the equivalent of a really expensive map with me so I didn't get lost on the way home. I did have to stop and use it for that exact purpose a few times. ;) I don't see a place to set preferred speeds, just "slower/faster" sliders and sliders for what types of roads I prefer. Even if I bias it completely toward "arterial roads" and away from highways/interstates it still puts me on I-90 for about half of the trip. :rolleyes: Maybe I have a different version? PM me if you have suggestions.

Update: after seeing that the winds weren't going to let up (still 15-20 mph out of the NW, the average direction I was travelling :( ) I decided to reroute it as much as I could. I ended up on some ...unexpected roads. :o Lets just say that given the choice between P&G on a gravel road (mostly "P" due to the insane increase in rolling resistance) and sucking it up on a secondary highway into a headwind, I now know which one to choose.

So long story short, it took nearly twice as long as it normally does, but added only about 20 miles (<10%). Last time I had similar conditions driving home (again about a 20MPH wind out of the NW) was thanksgiving of 2005. I had figured out enough about hypermiling by that time to avoid the interstate - I took secondary highways most of the way. The result was a paltry 44.0 on the MFD and my worst tank ever (I think calculated came out to be under 40). This time? 59.6 for the entire trip. :cool: The average temp was near 30.

I stopped twice, the second time to refuel.

66.7 / 75.1 miles
65.4 / 70.8 miles
54.1 / 153.7 miles

Can you tell where the river valley is? ;)

Those first two segments weren't enough to pull me under 70 for the tank - I finished at 70.8 / 563 miles. Calculated it came out to 72.0. Yay record tank!! :D

Not quite sure what I'm going to do on the way back yet. The forecast shows the winds dying down and maybe even shifting to being light out of the SE! Argh.

Edit: I've got the grill block still on, but what are "wheel skirts"?

.6 for the entire trip. :cool:
Edit: I've got the grill block still on, but what are "wheel skirts"?

Wheel skirts are those covers over those back wheel wells of the Honda Insight. They are easy to do for the back wheels, more difficult to do for the front wheels. I have skirts over all four wheel wells on my car (see my avatar).

Thanks basjoos - I'll look into that. :cool:

Update again: I ended up compromising somewhat on the way back, taking major county roads and a few stretches of secondary highway instead of *really* back roads. Without that nasty headwind, and with 10-15F warmer temps, I managed 67.3 for 303.5 miles. :D

I can't credit much of this improvement to some sudden change in my highway technique though - there was a significant amount of 30-40MPH P&G on those mostly deserted secondary and tertiary roads. ;)

I did notice that at least for me, 1700RPM steady-state on level ground translates to 45-50 IMPG. Either that would maintain or gradually increase speed. I'm still wondering how that + the occasional warp-stealth can translate to 65MPG at 55MPH? Those stretches of highway for me were still right around 55MPG. :(

... I have skirts over all four wheel wells on my car (see my avatar). We would like to see a bigger picture, pleeaase,

Pierre M.

OK, I will add my word.

I do a lot of HW so, I am interested by the thread.

For the moment, on HW, I flirt with the 59MPH giving approx. 50MPG. Last friday, I saw anything else than a Wal-mart (Let say a Canadian-tire (be patriot:D )) coming in my miror. So let's draft for the first time. I had to increase the speed to 65MPH but suprise, the MPG jumped to 65 (3.5liter/100km). Fortunatly, there is almost no trucks on the HW I take, fortunatly because I will not to make the choice between better MPG and the new paint of my new car :rolleyes:

Pierre M.

We would like to see a bigger picture, pleeaase,

Here's his whole process in detail:
http://www.gassavers.org/showthread.php?t=774