Fuel economy at 65 mph vs 60 mph

None!
Drop the speed to 50 and you might see some.

For us, it's the RPM's. On level ground, any faster than about 63 and the RPM's go up. I associate that with fuel economy.

At that speed it depends on the road. With I gears in my X it would stay in overdrive at 70 and not at 65 and mileage was better at 70, BUT it was way better at 60.
If the difference between 7 and 10 MPG is going to make or brake you it's time to rethink your choice of RV.

I run at 70 on the interstate. Right in trucks torque band, doesn't "labor", w/ A/C and grossing close to 22,000 lbs nets 10.5 mpgs. For the longest time, many states had split speed limit for semis and cars. Was touted as a "safety" means, but in reality it was (A): Revenue maker for states and (B) a target for semis as cars would come up on them very FAST and not realize it and bam = accident.

If on 2 lane road, I run at 60. Otherwise do posted speed due to traffic or congestion. MPG's here are negligent.

I have a DP with a Cat C7 that I try to run at about 62MPH but that engine likes to go. I'll often find myself up at 70MPH. After a time or two at that, I'll set the cruise control. There has to be a fuel savings at the slower speeds, but I've never noticed it as I don't keep track of my fuel usage.

Bill

We don't really care about fuel mileage anymore. I look at it this way. We just spent 21 days and 2200 miles on the road having fun, Fuel + RV parks came out to $78.00 a day over the whole trip. Out west here you cant even stay in a decent hotel for $78.00 a night and you would still have fuel cost. When ever anyone says wow what mileage do you get pulling that fifth wheel. I just ask them can you do the same things I do cheaper than $78.00 bucks a day????? My thought is if I need to get a certain mileage 12mpg not 9mpg It is time to stop traveling and just stay home, like most the people that ask me wow what mpg do you get pulling that fifth wheel. I understand people have a budget and this way of thinking is not for all, But it cost to travel so you pay gas or you pay hotels.

johndeerefarmer wrote:
What fuel economy increase have you observed from pulling your fiver at 60 mph vs 65 mph?

Less than .5MPG. When you are pulling something as aerodynamic as a brick wind is more a factor than speed. The A/C counts too.

My rig gets 12 MPG at 60 MPH. It gets 9-10 MPG at 70 MPH. I'd probably do better if I didn't have 4.88 gears in the rear.

I went from 9.4 to barely 9.

The question from the OP is too broad. Everything depends on the roads, gradient, engine, rear end gearing, weight of TV, weight of RV, height of RV, and on and on...

How do you know when you've exhausted all reasonable topics of discussion on a RV forum...