finding right cruising speed for economical gas mileage

[shark14]

We just purchased a used 2008 Winnebago View with 5400 miles. Does anyone know a good speed to travel at to get the most out of the mileage? It is a V-6 diesel motor.

[Harvey51]

Time for a physics lesson. The force of friction is proportional to the square of the speed. It means doubling speed uses four times as much fuel. Going ten percent faster uses 20% more fuel per mile. You can see it on a graph here: https://www.fueleconomy.gov/feg/driveHabits.jsp
This doesn't depend on the vehicle size or shape because it is comparing a vehicle to itself at a different speed.

Safety also increases non-linearly with decreasing speed because the energy to be dissipated in a crash is proportional to the speed squared - down to the speed of traffic. There is something magic about all the vehicles going the same speed: no passing means MUCH safer.

I mostly drive the MH on two lane roads. I like to go just a little below the speed limit but will speed up to go with the flow, then get off the road when opportunity presents and let all those folks in a hurry go on by.

[Bordercollie]

Seems that most everybody moans about gas prices but they jam from stop light to stop light as if they don't care in their huge pickups and Suburbans and SUV's. I try to drive a MH at around 55 to 60 mph and enjoy the ride. If local yokels want to ride my rear bumper, I'll pull over and let them pass when it's safe. When I am on an unfamiliar twisting down grade, I obey the speed limit signs and ignore the yokels. They are not driving a top-heavy motorhome.

[Gjac]

KD4UPL wrote:
Around here the minimum speed on interstates is 45 but the limit is 70. Are you saying everybody is happy if you poke along at 50 in a 70? I'm pretty sure they're not.

OP, slower is the answer to a point. You need to be at the engine's peak torque RPM while your transmission is in it's top gear. That should theoretically be your best MPG.

This is basically what I do. My transmission shifts into 4 gear at 45 mpg on a flat road, if I travel at 50 mpg it will not downshift on slight hills. Also by not using cruise control and accelerating slightly I can keep it in 4th gear without downshifting when approaching a hill. I also still use a vacuum gauge to drive(I'm old) and know when it will down shift based on vacuum readings so I take my foot off the pedal and reduce speed before it downshifts keeping it in 4th gear. If you have a 5 or 6 speed your speed will be higher.

[KD4UPL]

Around here the minimum speed on interstates is 45 but the limit is 70. Are you saying everybody is happy if you poke along at 50 in a 70? I'm pretty sure they're not.

OP, slower is the answer to a point. You need to be at the engine's peak torque RPM while your transmission is in it's top gear. That should theoretically be your best MPG.

[Jim_Shoe]

The only way a MH will get good gas mileage is if you drive it over a cliff, but the sudden stop at the bottom is uncomfortable. I've found that driving about 5 MPH over the minimum speed limit on expressways results in less downshifting out of overdrive and allows everybody to pass me. Then everybody is happy. Based on the number of hours I plan to drive, I know about where I'll be at the end of the day so that I can call for a reservation if its a popular area. It helps if you don't have a time limit on your trip, as in "retired".

[skipnchar]

Your mileage will ALWAYS be best when you travel slower and more steady. slower speeds mean less wind resistance which equals better economy and steady speeds means using less fuel to achieve the speed you've chosen to travel. Hit the interstate at a constant 35 MPH and never let up and you'll do best regardless of what you're driving. OF course it's hard to imagine you'd enjoy traveling that way even if you weren't arrested for obstructing traffic. My advice is to travel at a speed where you enjoy the trip the most whether that's 80 MPH and 6 MPG or 50 MPH and 12 MPG. The trip to where you're going SHOULD be as enjoyable as being where you're going.
Good luck / Skip

[powderman426]

As mentioned above there is scangauge but a less expensive way to go is with a ELM bluetooth that plugs into the odbII port and sends the data to your smart phone or other android or apple device with bluetooth capability. It costs less than $10 and the Torque app is free or $5 for the version with more features. You can find it here It's very useful for mileage and many other data points that are there but not being displayed. You can even scan for and reset codes with the updated app. Lots of functionality for very little money.

[Francesca_Knowl]

I realize that you already know that speed's the biggest factor, but thought you might be interested in the following tool that tells you just how much it affects a particular rig. I think the site assumes gas-powered, but since it's based on "advertised" mpg at 55 mph, I doubt it makes a difference.

Link to fuel use calculator

[Trackrig]

We're in a DP, but the best speed for us is 62 on cruise control.

I also have a Scan Gauge for my diesel that helps with the mileage. In itself, it doesn't do anything, but it gives you a lot of info that will help you conserve fuel. Look it up on line or next time you're at a CW.

Bill

[gbopp]

Welcome to the forum. Slower is usually more economical.
In our Class A gas Southwind I usually travel about 58-62 mph. That gives me the best mileage and isn't unreasonably slow.

I don't know about a diesel but, I would think the same is true.