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Old 11-11-2020, 12:34 PM   #1
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Fuel Consumption and Safety Margin

Hey guys

just getting into overlanding and preparing my van for a first off the grid "dirt road trip".

One of the main questions I couldn't really find an answer to is how to "calculate" your fuel consumption.
And before starting my question: I know it's always good to carry more fuel than you need, even you'd give it to someone you ran empty...
And I'm only talking "dirt road/ gravel/ sandish" (=easy) conditions into account and not talking about "heavy lifted Jeep rock crawling" trips.

Now let's go with the following:
On a trip from San Francisco to Lake Tahoe I got 12mpg "uphill" and ~20mpg "downhill".
The trip is ballpark 200 miles in each direction on paved road, mainly high way.
Typically I can get 400miles with a full tank on a regular road trip.

How does that change going easy overlanding?
I think about something like the 140 mile Mojave Road (flat example), thinking about the 200mile Tahoe Backcountry Discovery Trail (mountains/ climbs),...

--> How can I expect my fuel consumption to change?

Mojave Road: I guess I can make it...
Tahoe trip: I think it could get tight...at least my buffer wouldn't be comfortable...

Does that sounds about right?

How do you calculate?
Do you go for any proportion "distance to elevation gain"?
Adding 10% more for a rocky trail vs. a gravel road, 30% more for mountain area vs. flat?
Do you just expect 50% higher consumption compared to usual road conditions?

Looking forward to learn from your experience!
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Old 11-11-2020, 01:13 PM   #2
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50% more is a good starting point. Crawling does actually seem to use that much more, but also, you might run into fuel starving issues on steep grades if you have under a quarter tank. I carry 10 extra gallons normally.
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Old 11-11-2020, 01:18 PM   #3
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I normally figure half my on road mileage. Sand, mud, deflated tires and 4wd will drastically reduce your range. As for the Mojave road, there are numerous spots where you could bail out and hit the pavement to a gas station if needed, but your probably fine. Personally, I always carry some extra fuel, but rarely need it, yet it provides a certain level of comfort.
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Old 11-11-2020, 02:34 PM   #4
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What engine, 2wd or 4wd, will you air down your tires, long and straight off road stretches or a lot of curves? There's a lot that goes into the assessment (guess) so I think the 50% estimate is a good place to start.


You also have to think of the consequence of running out of fuel. Gas engines you just add more fuel and crank away, modern diesel engines it can quickly get far more complicated to prime a diesel engine.


Do you have a factory tank, or a larger aftermarket tank? Also, do you have a bumper setup with the ability to carry extra fuel?




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Old 11-11-2020, 10:27 PM   #5
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Four wheel drive in high range or low range also makes a difference.
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Old 11-11-2020, 10:37 PM   #6
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Thanks for your thoughts so far!

My van is more or less a stock 5.4l RWD. Not lifted, have new springs and shocks in, 245/75R16 Wildpeak AT/3W.
Max rear tire pressure for full load is at 80 (E rated tire).
As I‘m somewhere in the mid range of load capacity I drive 65 rear on the road. For the dirt roads I plan to go down to 45-50 and give it a try.
The tank is also stock.

I‘m getting my gutter clamps next week and will be adding a roof rack, so that I can load emergency stuff up there. I plan to go for 1 Jerry Can, tool box (like some hand tools, tow stuff, de-/inflator, ...) as well as the medi kit.

So all in all it sounds like a 50% increase in consumption is fair seeing the roads I can go take with this vehicle.
But looking forward to get more comments.
Perhaps even examples: how much more would you calculate for Mojave Road? Or Pioneertown to Big Bear (which I already with the van)? Death Valley for the 2WD high clearance roads?
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Old 11-11-2020, 10:43 PM   #7
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I recommend getting a ScanGauge, then tracking fuel economy for representative conditions. And don't forget idle fuel consumption. My V10 burns 0.6 GPH at idle, or 0.7 with more A/Cs cranking.

Also, beware that adding a roof rack is a pretty good hit to fuel economy on its own, for highway driving. You'll probably lose 1-2 MPG right there.

If it makes you feel better... If I'm dragging my trailer up steep, primitive forest roads and trails, I'm usually only seeing 1.8-2.2 MPG. At least it's never gone to GPM!
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Old 11-12-2020, 06:50 AM   #8
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Quote:
Originally Posted by carringb View Post
I'm usually only seeing 1.8-2.2 MPG. At least it's never gone to GPM!
Ha, Ha - You only need to have filled up a pair of 250 gallon tanks on a vessel one time to appreciate that!
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Old 11-12-2020, 01:57 PM   #9
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Originally Posted by Twoxentrix View Post
Ha, Ha - You only need to have filled up a pair of 250 gallon tanks on a vessel one time to appreciate that!
True enough. My 50ft boat got a steady 1.2 mpg's in average sea conditions, less in stormy weather. After that, anything is an improvement.
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Old 11-12-2020, 04:07 PM   #10
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I've run Mojave Road countless times at speed and lots of throttle in right at 4 hours (usually just shy of 30mph avg moving speed) moving time end to end and typically get 7-8 mpg and use half of a tank. I do carry an extra 10 gallons normally but that just makes me feel good. You can jump out at Kelbaker road and get fuel in Baker if distance is a concern.

V10/4R100, 35s (15-20 psi offroad) with 4.56 gears, 9city/10hwy normal avg, 8k loaded with gear and spares

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