Americas Why all the fuss about fuel economy?

[LeeroyJ]

I'm extremely skeptical about both the mileage reported by the onboard computer, and the mileage reported by people on this and other forums. If you add anything that negatively impacts airflow or adds weight, you are likely negatively impacting your fuel economy. A roof rack, roof top tent, lift, larger and/or wider tires, MT's instead of AT tires, external moley panels, bull bar, extra lights, sidesteps/sliders, etc. etc., they all impact MPG negatively. Your average speed for a trip will also impact MPG, in an exponential fashion (or at least not linear). Add a headwind, climbing altitude, colder temps, etc., and there can be some major differences in one drive to the next even if you haven't changed anything on the vehicle itself.

All that being said, I wouldn't expect an impact of 30% for adding a low-profile roof rack. You need more data.

In addition, the only accurate way to measure MPG is to first fill the Grenadier and record the mileage. Then drive. When you fill up again, you know accurately how many gallons you used and you can subtract the new mileage to figure out how far you drove. In my experience my real economy has been substantially less than what the computer shows me getting.

This is why for me, the Longranger extended fuel tank is my most important mod.

 

[Zimm]

I am looking for feedback on what kind of a fuel economy hit folks have taken from mounting different kinds of roof racks.

I mounted four INEOS Grenadier: DualTrack™ Low-Profile Roof Rails from DVAmechanics on Saturday and then drove about 120 miles yesterday, most of that distance at 70 to 75 mph. The fuel economy appeared to be reduced by approximately 30% (I will start a more controlled test when we hit the road again tomorrow). This probably explains why the onboard software caused the fuel bong to go off when I had only used 15 gallons (usually it goes off closer to 19 or 20 gallons down). (I filled the tank yesterday to confirm how far down the fuel level was.)

I didn't buy a Grenadier to save the planet and gasoline is cheap, but even with those givens I am not happy with what appears to be a dramatic reduction in range (something which appears to far outstrip my ability to compensate with the rear mounted jerry can support I am trying to figure out how to install).

I really want to believe my problems are caused by something else; I had not driven the truck more than a very few miles since having my 20,000 mile (second) service check at my dealer a week ago so I am desperately hoping it's their error. For what it's worth, the roof rails are really quite elegant. They have an extremely low profile (3/4 inch height increase) and seem to be incredibly adaptable. While my arthritic hands could have done without the tighening (and loosening and retightening) of 64 different sized hex screws, the overall product fits well, looks good, and appears to be almost infinitely adaptable -- it's also eminently affordable if you're willing to do your own assembly. But this isn't a snap on / snap off design: removing the four bars (even without disassembling them) will require removing 32 of those hex nuts and (for this old man) a good hunk of time.

My fuel economy was a pretty consistent 14 to 15 miles per US gallon before I mounted the roof rack. I should have a more precise sense in a couple of days what it is now.

You realize, even if your number is solid, which it isn't, but let's just say it is, this has NOTHING to do with the grenadier. The shitty aerodynamics of roof rails and whatnot, do not impact any car any more than any other car the same product is put upon.

 

[Guvnor]

I'm extremely skeptical about both the mileage reported by the onboard computer, and the mileage reported by people on this and other forums. If you add anything that negatively impacts airflow or adds weight, you are likely negatively impacting your fuel economy. A roof rack, roof top tent, lift, larger and/or wider tires, MT's instead of AT tires, external moley panels, bull bar, extra lights, sidesteps/sliders, etc. etc., they all impact MPG negatively. Your average speed for a trip will also impact MPG, in an exponential fashion (or at least not linear). Add a headwind, climbing altitude, colder temps, etc., and there can be some major differences in one drive to the next even if you haven't changed anything on the vehicle itself.

All that being said, I wouldn't expect an impact of 30% for adding a low-profile roof rack. You need more data.

In addition, the only accurate way to measure MPG is to first fill the Grenadier and record the mileage. Then drive. When you fill up again, you know accurately how many gallons you used and you can subtract the new mileage to figure out how far you drove. In my experience my real economy has been substantially less than what the computer shows me getting.

This is why for me, the Longranger extended fuel tank is my most important mod.

Don’t forget the trip computer is showing MPG in IMPERIAL gallons NOT US gallons that are approximately 20% larger. Do the maths and you’ll find it’s more or less 15 MPG as declared by Ineos.

 

[Zimm]

Don’t forget the trip computer is showing MPG in IMPERIAL gallons NOT US gallons that are approximately 20% larger. Do the maths and you’ll find it’s more or less 15 MPG as declared by Ineos.

US trucks are set to US gallons not imperial.

 

[Tenac]

US trucks are set to US gallons not imperial.

I would hope so or that is some half A$$ stuff. lol

 

[LabRat]

US trucks are set to US gallons not imperial.

You sure about that? The + and - for cruise control certainly isn't in MPH.

 

[DefenderGuy]

In addition, the only accurate way to measure MPG is to first fill the Grenadier and record the mileage.

I agree completely. The only reliable way to record MPG is to fill the tank all the way up, drive, record the distance, and then fill the tank all the way up once again, compare the gallons purchased to the miles driven and calculate the MPG number.

That said, as I explained, the low fuel bong (which normally occurs when the tank is down 19 or 20 gallons) went off yesterday when the tank was only down 15 gallons. And I had driven a lot less than 210 to 225 miles.

There's obviously more testing that I'm going to do. What I asked was simply whether anyone who had installed a roof rack had quantified what if any impact the roof rack had on real mileage, i.e. mileage that has nothing to do with anything reported by the stupid computer but is based solely on miles driven between two identical fillings of the tank to the top. (My question has nothing to do with a loaded roof rack -- with it's additional height and wind resistance -- causing a drop in MPG.)

FWIW, we drove about 65 miles on country roads today (in order to hike a small portion of the Appalachian Trail in northwestern Connecticut) and the onboard mileage computer (which I agree appears to be hardwired to report MPG using Imperial gallons) was looking much closer to normal ("17 mpg") by the end of the day, but I haven't refilled the tank so I don't have any independent verification.

You realize, even if your number is solid, which it isn't, but let's just say it is, this has NOTHING to do with the grenadier. The shitty aerodynamics of roof rails and whatnot, do not impact any car any more than any other car the same product is put upon.

Excuse me? Who said I was criticizing the Grenadier? Please, it's not unreasonable to want to know what (if any) the aerodynamic cost of a roof rail is (especially when there's an unexpectedly low mileage following installation). For the record, I think the DVAmechanics product is very well engineered and probably relatively low impact given its impressively low profile. If anyone (using real MPG figures) has actually measured the impact of roof rails on mileage, I would simply like to know what their product was and what their analysis determined. That was my question. I am trying to troubleshoot.

 

[anand]

I am looking for feedback on what kind of a fuel economy hit folks have taken from mounting different kinds of roof racks.

I mounted four INEOS Grenadier: DualTrack™ Low-Profile Roof Rails from DVAmechanics on Saturday and then drove about 120 miles yesterday, most of that distance at 70 to 75 mph. The fuel economy appeared to be reduced by approximately 30% (I will start a more controlled test when we hit the road again tomorrow). This probably explains why the onboard software caused the fuel bong to go off when I had only used 15 gallons (usually it goes off closer to 19 or 20 gallons down). (I filled the tank yesterday to confirm how far down the fuel level was.)

I didn't buy a Grenadier to save the planet and gasoline is cheap, but even with those givens I am not happy with what appears to be a dramatic reduction in range (something which appears to far outstrip my ability to compensate with the rear mounted jerry can support I am trying to figure out how to install).

I really want to believe my problems are caused by something else; I had not driven the truck more than a very few miles since having my 20,000 mile (second) service check at my dealer a week ago so I am desperately hoping it's their error. For what it's worth, the roof rails are really quite elegant. They have an extremely low profile (3/4 inch height increase) and seem to be incredibly adaptable. While my arthritic hands could have done without the tightening (and loosening and retightening) of 64 different sized hex screws, the overall product fits well, looks good, and appears to be almost infinitely adaptable -- it's also eminently affordable if you're willing to do your own assembly. But this isn't a snap on / snap off design: removing the four bars (even without disassembling them) will require removing 32 of those hex nuts and (for this old man) a good hunk of time.

My fuel economy was a pretty consistent 14 to 15 miles per US gallon before I mounted the roof rack. I should have a more precise sense in a couple of days what it is now.

My LFD Off Road rack was a negligible hit on fuel economy after already adding the weight of the drawer system (incl. fridge, second battery, etc) and 33s.

I would say the decrease from no rack to the 3/4 rack was maybe .2-.3mpg? Going to the full length rack with a solar panel, Maxtrax, and hi-lift mounted up there was maybe 0.1-0.2mpg of a hit?

With ~800-900lbs of weight added to the truck (not including people), the full rack and stuff on the roof, 33s, etc, I was still maintaining somewhere in the 13s driving from MD to UT and back, with cruising speeds of 80-87mph most of the time.

 

[Guvnor]

US trucks are set to US gallons not imperial.

Hmmmmm…. Are you absolutely sure.?
In that case I’m getting MUCH better MPG than expected 18-19 over the last 2,000 miles and I don’t hang around. If you work that out to Imperial it’s exactly 15 mpg.

I gave up doing the calculation by ACTUAL mileage & ACTUAL gallons as over the last 6 fills it was consistently circa 15 mpg.

 

[Tazzieman]

You guys must be driving the same flat route all the time!
No way can I calculate average economy.
And if I could or did , would I drive the car less? No!