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iquailhunter · 03-25-2013, 08:44 PM

I noticed on another thread earlier that someone had been told by an Entegra factory rep. that there is a considerable difference in the fuel mileage between an Anthem and Cornerstone. Would really like to hear what the owners have to say about this. I know that all of this will depend on lots of different variables (driving speeds, weight of toads, flat or mountains, acceleration, etc.) but would like to get a "feel" for what everyone is experiencing.

Let the fun begin

Mr_D · 03-25-2013, 08:49 PM

I wouldn't even consider the fuel mileage when looking at a new rig, it's really a minor part of the cost of ownership.

DSL417 · 03-25-2013, 09:02 PM

I can't speak Cornerstone, but I have to say...it REALLY depends.

I have averaged as little as 4.9 mpg (quartering, head, or crosswind of 30-45 mph winds and a hellish 300 miles) to 9.5 mpg (flat with tailwind of 20-25 mph).

Overall, I have averaged about 7 mpg over 3000 miles the last three months, pulling 7500 lbs of pickup and Harley. I usually run at 60 mph on the cruise.

That also includes 81 hours of generator and quite a bit of aqua hot usage in the last month.

X2 on cost of ownership. If you can afford the Cornerstone, the the gas milage diff between Cornerstone and Anthem is a minor cost of ownership.

iquailhunter · 03-25-2013, 09:05 PM

The question was not asked to determine what I wanted to buy. I am just curious about the real difference in fuel consumption between the two models.

DSL417 · 03-25-2013, 09:14 PM

Sorry, I should have noted and thought about the person asking the question as I know you have a new rig. So what are you getting?

Cruzer · 03-30-2013, 11:49 AM

These are always interesting comparisons. The biggest problem is in getting accurate comparisons. Engines are like big air pumps and the more air they pass, they more fuel they also pass. In an ideal world a small displacement engine turning at slows RPMS would give you best fuel economy. However, you can only move so much weight so that's where the compromises come in.

The big 600 HP ISX in the K3 has a larger displacement engine than the Mountain Master's 450 HP ISL so it's going to move more air. However, there is so much bottom end torque in that engine that it dosn't need to downshift as much so it keeps it's revs lower. Also, the final drive ratio is lower due to the taller rear axle gearing so that also keeps the revs lower during normal cruising speeds. I would suspect that one helps offset the other but probably doesn't completely compensate so the ISX probably moves more fuel through it.

The biggest factor in any fuel calculation is wind resistance. Driving at 10 MPH produces 100 pounds per square foot (PSF) of wind resistance. On a typical motorhome that's 10,625 lbs of resistance due to the large frontal area.

At 55 MPH that goes up to 3,025 PSF, which is around 321,406 lbs of total resistance. Yes, it takes horsepower to move that air out of the way so the fuel usage goes up as the speed increases.

At 70 MPF it goes up to 4,900 PSF, which equates to 520,625 lbs of total resistance. At 80 MPH it goes up to 6,400 PSF, which yields a wopping 680,000 lbs of resistance. You are trying to move 340 tons of air when driving at that speed so you will burn some serious fuel at 80 MPH. Many drivers report that they will see a 1 MPG difference for every 10 MPH at highways speeds so driving 55 versus 75 will take you longer to get there but you'll make less trips to the bank to withdraw fuel money.

Also, keep in mind that a 20 MPH headwind when driving at 60 MPH is the same thing as driving at 80 MPH with no headwind.