How big is the engine? Sometimes bigger is better. You aren’t working it so hard for the task at hand.

I have always heard 5–6 max. Most of the big Class A ones aren’t the least bit aerodynamic – sort of like a Greyhound bus with fewer windows.

There is one (the Avanti) that gets 15 MPG, but if you read, you will see that it has things that most Class A motorhomes lack, like aerodynamics, to justify it’s claim of, ”... up to 70 percent better fuel economy than comparable Class A motorhomes.”.

A bit of other searching shows that 6–8 MPG is, indeed, typical… for diesels. Gassers don’t have the torque so (as @bkcunningham says) they have to rev higher and work harder.

All I can say is our 32’ RV got 9 mpg of gas.

@bkcunningham These usually have 350 CID diesels (Cummins or Allison).

@jerv Interesting . I see the Avanti is ” 12 inches closer to the ground and 6 inches narrower”. It also has a sloped front. I can believe it is better but still, I’d be hard pressed to believe 15 mpg! It still has a GVWR of 18,000 pounds.

I am going to make an estimate and figure a conservative 8 mpg on the highway at 65 mph for a typical 40 foot Class A. I can’t be too far off, can I?

Well, MPG claims are often inflated if for no reason other than real-world driving is nothing like the EPA test cycle.

For a typical 40-footer, I would say 8 would be a little optimistic, but doable if you are on level ground and not towing anything. I would guess closer to 7.

A few years back I ran into an English couple who were touring the US in a loaded Renault Camper that looked like and was the size of a UPS truck. They were getting 22 MPG highway when my 97 F150 was lucky to get 16 mpg. WTF!

@rojo See? It is claims like that that make me wonder. The laws of physics are hard to beat. Maybe they were always driving at 50 MPH – with tailwind.

@jerv Thanks for reminding me about towing. They are towing a Chevy Cruize too. That has to make the mileage even worse.