Is it still Ecomodding if you drive 85?
 

I have family in PA that I have not seen in almost 2 years due to the global pandemic. My elderly father and I have gotten our vaccines so I will be leaving on a road trip tomorrow to drive back solo to see him in person. I will be traveling on I-80 for parts of the trip and the legal speed limit is sometimes 80mph out here.

I have done some mods to the Golf TDI, most notably a full belly pan. I have been hypermiling almost the whole time I have owned this car. I wonder how low my mpg will go if I set the cruise control at 5 mph over the speed limit for the duration of this trip? I expect my 90 day average to drop quite a bit for a while but it is a long trip and I don’t want to add extra time to save my average mpg.:rolleyes:

High speed can absolutely murder your fuel economy.
I suggest picking a speed and sticking to it regardless of higher speed limits.
What matters for travel time is average speed, not topspeed.
80 mph is just under 130 km/h, a TDi might get acceptable fuel economy at that speed.
But beyond that it starts getting worse exponentialy.
I suggest 110-120 km/h maximum.

Worst I've ever gotten was 35L/100 km (8 mpg) in an Audi TT with 180 PS 1.8 TFSI at 250 km/h (156 mph)

Have you done anything in back to reduce your wake ?

I had considered building a removable boat tail for this trip but that didn’t happen so no, big old dirty hatchback wake.

P.S. after I cross the Mississippi the posted speed limits are much lower. Wyoming has the highest speed limit and I will only be on that section for 90 miles.

I'm eager to see what kind of numbers you get !
If you have a trip computer, please take note of your instant mpg when you are averaging 85 mph.
I'm considering a Chevy Cruze diesel, so I'm especially interested in the results you get.

Btw, the 2016+ Cruze diesel has a .28 cD ( i think I remember .28, it's either .27 , or .28 )
Older than that had a .30 ( both numbers are for the sedan.

Do you know your cD ? ( Or cDxA )

I seem to recall .30 ish, and newer at .29 ?

Why didn't you ask sooner? :snail:

Compact camper alternative: New Beetle TDI with hard mounted pop up tent
tinypic ate all the pictures, It was a New Beetle with an originally top-monted tent that he moved to where a notvhback would be, clamped to the roof and trailer hitch.

If you should ever make a pop-tent here is the design I found at Permalink #57, that picture is still there:

https://static.dezeen.com/uploads/20...-1704x1132.jpg

Mounted in the wrong place, of course. With an inflatable floor, it would weigh about as much s a backpack.

Ontopic. It's family Panzer Vor! Hammer Down!

Aero mods are way more important at 80mph than at 55mph.
That diesel probably needs a good Italian tune up.

Fuel efficiency at higher speeds is mostly aerodynamics and gearing.
Rolling resistance (in W) grows proportional to speed, aerodynamic drag by cube.
That's also why I suggested picking a speed and sticking with it, as it's the most efficient way to archive a high average speed.
Pulse and glide also doesn't work above a certain speed as you're running your engine close to maximum efficiency regardless.

On a sidenote:
In an older Mercedes Benz E200D (2,2L turbodiesel, 6-speed manual, wagon) I archived peak fuel efficiency at 110 km/h or about 70 mph.
However these things somehow are very aerodynamic and geared ridiculously tall.
In my Spyder that's impossible to archive since I'm spinning over 3000 rpm at that point at a rather low load.

Unfortunately we only got the 5 speed in the Mk IV here. I will keep everyone posted as I go.

I have a ScanGuage II and will report back.

Thanks for the link to the rooftop camper freebeard. Perhaps my dismal economy at speed will motivate me to do something about the wake in the future.

Happy to help. I can imagine a trunk-mounted tent that unfolds sideways to either side to keep the fore-and-aft dimension under control. Let me know when your ready and I'll work up a proposal.

That one in the picture looks like it would be removed and placed on the ground.

The first leg was not dismal
 

Today did a shorter drive of only 232 miles to spend a night with my wife’s family east of Cheyenne WY. This leg included most of the 2 lane roads for the rest of the trip. Speed limits were adhered to through towns. On the open roads I generally stuck to my goal of 5 over although at times it was 10 over. I generally get good mpg traveling this direction due to a few unique factors.

1. Elevation- After the first 50 miles much of the trip is at over 8,000’ above sea level. With a slight downhill grade I will show 130 mpg or higher at 75 mph. The thin air really helps mpg.

2. Favorable winds- On I-80 the wind was 26 mph out of the west/northwest, a strong tailwind.

3. Mostly downhill from the continental divide east of Laramie to Cheyenne. It is generally rolling but in 40 miles goes from 8,500’ to 6,300’.

Cd, you would have to drive this section under the same conditions that I did to get the crazy high numbers I was getting on I-80 at 85 (at times 80 mpg). Do not expect to get the same mileage at sea level, on the flat, on a windless day. I was still at 53 mpg for the trip when I got to Cheyenne. You climb again leaving Cheyenne and on the inclines I saw instant mpg drop into the 20s at times at 80 mph.

Stats for the day- 232 miles in 3.6 hours @ 63 mph average speed.
49.2 mpg for the day. 4.7 gallons of diesel. (From the ScanGuage)

Look for summer fuel, should be available at big truck 'oasises' now.

Not bad considering...
 

Today started out before daylight with pea soup fog. Not a fun way to start a long day. I got a bite of breakfast and started east slowly as the fog lifted. It was replaced with 20-30 mph winds from the northeast. A quartering headwind catches the largest profile of the car. Traffic was light and I continued with my target of 5 over the limit. (The Mk IV VW speedometer reads 2-3 mph higher than the Garmin on the dashboard). However, much of the day was spent at an actual 5 over the 75 mph limit through Nebraska and Iowa.

Between freezing drizzle on the windshield, wind and light snow at times, I still managed 46.2 mpg for the day at an average speed of 70 mph. Luckily as the day progressed it slowly warmed into the 40s and the wind slowed into the teens out of the north.

884 miles, 19.1 gallons used, 12.6 hours of driving.

First half of the trip completed
 

Today was another big day. 600 miles to my destination. According to the ScanGuage I used 12 gallons of fuel and got 47.8 mpg for 9 hours of driving. I went through Indianapolis and Columbus and headed north toward Cleveland. Wind was pretty much 5 mph from the north all day. Traffic was mostly good and I was able to stay at “5 over” or 70 mph most of the day. The ScanGuage breakdown may have been slightly optimistic on mpg. The first 2 fillips hand calculated to 46.8 mpg from my home to eastern Indiana.

The storm that has been chasing me since I left Colorado should get here overnight. It could be messy here tomorrow but I won’t have much driving to do.

Slow to update, busy but a successful trip
 

I am updating now that I am home in Colorado. I only spent 3 full days in PA running around, trying to do everything that would have done in a week last year before COVID ruined that. I had a successful visit and will be going back out for a week in June. I made the return trip in just 2 long days of driving. I did stay briefly at a hotel in Davenport Iowa but between driving rapidly and taking brief rests, I didn’t have much time to post.

FWIW, back at the start of the trip, I got a check engine light while driving before daylight in WY in freezing drizzle and a strong northeast wind. It turns out I have a bad mass air flow sensor and was unable to get it replaced for the duration of the whole trip. This could not have been helping my mpg but the car mostly ran fine so “hammer down”. The ScanGuage likes about 8 hours of inactivity before it recalculated a new “day” so it did not separate the days when I was only at the hotel for 7 hours.

I put more details in my fuel log and that is hand calculated so it should be very accurate. I can tell you the wind was terrible and either some form of cross or headwind. The speeds were high and sustained- set the cruise to 5 over except in construction zones.

The quick stats- 1,685 miles and 37.8 gallons of diesel for 44.58 mpg for the return trip. I may post this in “Success Stories” because I am amazed it was not worse. This was days of driving at 75-80 mph for almost the whole day.

True enough, but I'm not the one who figured it out.

Your tale makes me want to overcome the streetability issues with the Dasher diesel. It sucks around town but it really likes to stretch it's legs.

Totals for the trip
 

I filled the tank at the start and end of the trip. Hand calculated totals are 3,697 miles door to door, 80.315 gallons of diesel used at roughly $3.20/gallon for a fuel cost of $256.

The turbo diesel Golf returned 46 mpg for almost 3,700 miles of fairly high speed driving.

I was on a different cross country trip years ago when an overtaking semi truck blew a tire near me. Pieces of tire and tread were flying everywhere. We avoided damage but a piece of tread literally skipped off the roof of the car. For this and other reasons I do not like to hang out near tractor trailers. There was much passing done on this trip but I was on usually on full boost of the turbo with the pedal mashed to the floor to get around quickly, the opposite of hypermiling.

Besides a Tesla is there another car out there that has this kind of power and can return this kind of mpg at these speeds?