Best fuel economy speed

Like Wolfe said, it's all about RPM's not MPH if you're going after MPG.

Really two different questions here. Speaking from DP perspective, gas will be slightly different.

Best economic speed, flat ground: At peak torque RPM in 5th (not 6th gear). This is from my ScanGauge D. This is generally too low a speed for safe highway driving.

Best economic speed, rolling hills: About 200 RPM above peak torque RPM in 5th gear (so that it does not downshift on every hill).


Best REASONABLE economic speed, flat ground: At peak torque RPM in 6th gear.

Best Reasonable economic speed, rolling hills: About 200 RPM above peak torque RPM in 6th gear.

Note: some manufacturers chose gear ratios that really don't give you a "good MPG" speed/gear-- to be in 6th gear, your speed is such that aerodynamic drag is significant.

At 55 mph I get 7.0 mpg
At 60 mph I get 6.5 mpg
At 65 mph I get 6.0 mpg
At 70 mph I get 5.5 mpg

Generally, I drive between 60-65 depending on traffic and the speed limit.
We have a D13 Volvo, 500 hp with 1,750 lb. ft. of torque weighing 55,500 lbs.

MM.

I have found around 62 MPH is about the best but I generally go 65.

I love the fuel "economy" questions. You are driving an apartment. You won't get good mileage no matter what speed you drive. The difference between 45 and 70 is about 1-2 mg. Which translates into almost nothing unless you are driving a LOT of miles. And all bets are off if you drive in hilly terrain, stop and go traffic, wind, loaded heavy, genset running, how many stops you make etc.. I stopped monitoring mileage years ago. I didn't buy a MH as en economical travelling vehicle. I bought it for convenience. I still pay less than airfare and hotels so regardless of mileage travel budget is friendlier. You also will notice almost no difference in MPG towing a car. Your car is in the slipstream and rolling along with almost no resistance. And your car gets unlimited MPG while towing. I figure if my budget is so tight that mileage is a constraint on my MH usage, I have no business owning one. Ignorance is bliss. Every now and then someone at the pumps asks me what kind of mileage I get, I tell them, pretty good for an apartment. For me, it's all about smiles per gallon, not miles per gallon.

For most vehicles with the frontal area of a motorhome the best fuel economy speed will be in the 35 mph to 50 mph range, which is not practical. So as slow as you can stand to run.

donn0128 wrote:
Too many variables to give an answer.
Motor, transmission, rear end ratio, load, tire diameter, peak torque, all play into your answer.

Exactly.

Back in our gasser days our V10 did better at 70 MPH than it did at 65 MPH. At 70 it was in its sweet spot, at 65 it struggled on even the smallest hills.

I also agree with the others that +/- 1/2 to 1 MPG isn't something I'm going to get too worked up over. Normally I want to get where I'm going.

Having said that I have found myself slowing down a bit lately. We just did a 1200 mile trip, I ran around 67 MPH most of the time.

59 MPH is where I get the best gas milage in my Winnebago gasser.

I drive at 62 when possible, may drive a little faster going through metro areas my best mpg is at 55 but with a days driving 62 turns out to be 55 so 55 would turn out to be 45 which would add an hour to our 250 mile preferred travel distance.

Too many variables to give an answer.
Motor, transmission, rear end ratio, load, tire diameter, peak torque, all play into your answer.