Is it still Ecomodding if you drive 85?

[COcyclist]

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.

[Autobahnschleicher]

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)

[Cd]

Have you done anything in back to reduce your wake ?

[COcyclist]

Originally Posted by Cd

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.

[Cd]

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 ?

[freebeard]

Why didn't you ask sooner?

Compact camper alternative: New Beetle TDI with hard mounted pop up tent

FreeBeard was right...what would we do if the MPG goes up!?!?
Thanks FreeBeard! I just returned home from a 770 mile round trip to Portland, lake Oswego and home! I returned home late last night and checked the hard mileage and found 770 miles, 15.6 gallons netted 49.3MPG! So as Freebeard suggested, what will we do if the mileage goes up?!?
Beetle w/o any attachments/slick top= ave 48mpg :{)
Beetle with factory VW Roof racks and CVT tent= 38mpg :/
Beetle with new areo-hitch mounted rack/CVT tent= 49.3MPG WhoooRah!
That is a gain of 11.3 mpg boys and girls!

the beautiful Multnomah Falls

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:



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!

[oil pan 4]

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

[Autobahnschleicher]

Originally Posted by oil pan 4

Aero mods are way more important at 80mph than at 55mph.

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.

[COcyclist]

Originally Posted by Autobahnschleicher

Fuel efficiency at higher speeds is mostly aerodynamics and gearing.
Rolling resistance (in W) grows proportional to speed, aerodynamic drag by cube.

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.

[freebeard]

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.