Five ways to improve your motorhome’s fuel mileage.
By Jim Brightly, F358406
September 2009
When I proposed to write this article last year, gasoline prices were approaching $4 per gallon with diesel fuel 25 cents to 50 cents per gallon more. To everyone’s relief, those historically high prices subsided, and fuel dropped to below $2 in some areas earlier this year. Unfortunately, the return to lower fuel prices didn’t last long, as the price per gallon moved higher earlier this summer.
There isn’t much you can do to change the price of fuel, but there are things you can do to coax more mileage out of each gallon of fuel you pump into your motorhome. By implementing one or more of the fuel-saving ideas below, you can make your fill-ups last longer, extend your travel plans, and save money.
Lose weight
No, I’m not saying you need to shed some pounds, but your motorhome could probably stand to lose some weight. You see, moving the weight of your motorhome requires power, which means using fuel. The higher the weight, the more power needed, and more fuel required to make that power. However, by cutting the weight of the motorhome, you also will reduce the amount of power “” and fuel “” needed to propel the coach down the highway.
Perhaps it’s time for you to put your motorhome on a weight-loss program by eliminating items that you no longer need to be carrying in its storage areas. One by one, pull out everything from your basement compartments, as well as the cabinets, drawers, closets, and storage areas under the furniture inside the motorhome.
With the contents of the motorhome laid out before you, use the “Rule of Three” to determine what goes back into the motorhome and what gets left behind. Here’s how it works. If you haven’t used an item during your last three trips, it’s probably unnecessary, so leave it at home. There are exceptions to the Rule of Three. If you do your own coach repairs and maintenance, keep any tools you may need to accomplish these tasks, even if you haven’t used them during the last three trips. The same goes with spare parts, such as fan belts, coolant hoses, water pump, etc.
You also will want to ask your traveling partner whether he or she is okay with the items you plan to remove. By doing this, you will avoid any potential differences of opinion during future trips when something can’t be found. Of course, if you remove an item and on a subsequent trip discover that you could have used it, consider adding it back to your carry-along list.
I suggest doing this type of clean-out at the end of each travel season when you’re removing all the consumables from the galley prior to long-term storage. If you wait until just before you begin traveling again, you’ll have a more difficult time recalling whether an item meets the Rule of Three.
Another weight-saving tactic you may consider is to travel without a towed vehicle. Keep very precise mileage records when towing and when not towing “” you may even want to plan a 100-mile test loop (such as the one I discuss in a following segment) and drive it with and without your towed vehicle behind your motorhome. Once you determine the amount of extra fuel needed when towing, you can figure out whether it would be less expensive to tow a vehicle behind the motorhome or rent a car for transportation if needed once you’ve reached your destination.
Maintain your tires
According to John Anderson, founder of the Recreation Vehicle Safety & Education Foundation (RVSEF), “Tires, being the most vulnerable component on an RV, are also the most overlooked.” In the old days, before computers, the Internet, and cable TV, all we had were three TV stations, AM radio, and much more time on our hands. To determine the best tire pressure, we’d simply coast down a hill with different pressures in our tires, and whichever pressure produced the longest roll-out was the pressure we used. It wasn’t scientific, but it seemed to work. Nowadays, we have a lot less time and much heavier vehicles, and we’ve learned more about safety, so we must rely on the manufacturer’s weight label posted near the driver’s seat.
For those of us who carry much less weight in our coaches than their gross vehicle weight rating (GVWR), however, following the manufacturer’s psi guidelines might well produce a hard, stiff ride; banging pots and pans; and noisy dish cabinets. Instead, look to the RV tire inflation tables made available by Goodyear and Michelin, if those are the tires you are using on your motorhome. (Other tire companies also may have inflation tables available.) By adjusting your tire pressures according to recommendations found in these tables (available for download at www.goodyear.com/rv/ and www.michelinrvtires.com), you may get a quieter, more comfortable ride.
Inflate all tires on the same axle to the same pressure. Although this may cause a difference in the tire patch (the area of tire tread in direct contact with the ground surface) if your coach is significantly heavier on one side, there are other considerations, such as spring rate, that dictate using the same pressure. (The ultimate solution is to balance your coach so that each tire on each axle is carrying approximately the same load.) Check your tires’ air pressures at least once a month, before each trip, and each morning that you’ll be traveling. Inflation pressures should be checked when the tires are cold “” that is, before they have been driven one mile. Heat generated during driving increases air pressure above the proper cold inflation pressure. This elevated pressure is normal, so never “bleed” air from a hot tire, since this could result in dangerous under-inflation.
You also should check the age of your tires. The “birth date” of each tire is molded into its sidewall. Find a string of characters that begins with the letters “DOT.” The last four digits (or three digits for tires made before the year 2000) indicate the tire’s date of manufacture. The first two digits indicate the number of the week, starting with week “01” in January. The last two digits give the year. So, for example, if a tire was produced in the second week of June 2003, the number would be 2403. How old is too old? As a rule of thumb, the average life of an RV tire is six years. But factors such as the load, the tire’s inflation, sun damage, ozone pollutants, your driving speeds, and frequency of use are just a few factors that will affect tire life.
Tires will wear out faster when subjected to higher speeds as well as hard cornering, rapid starts, sudden stops, frequent driving on surfaces that are in poor condition, and when they are out of balance. Drive slowly and carefully on surfaces with potholes, rocks, or other objects that can damage and unbalance tires and cause wheel misalignment. Before driving at normal or highway speeds again, examine your tires for any damage, such as cuts or penetrations.
When you buy new tires, have them balanced when mounted, and only use a shop that balances with a computerized high-speed spin machine. If you’ve driven several times on broken, uneven, or rough roads, it would be a good idea to have the balance checked each time you have the tires rotated. Having this done could save you time and money down the road.
The bottom line is this: Tires that are properly inflated and maintained will last longer and give a better ride, providing an improved window for better fuel economy.
Maintain your chassis
According to Robert Henderson of Henderson’s Line-Up, Brake, and RV in Grants Pass, Oregon, who presents driving and handling seminars at FMCA international conventions, maintaining all of the various components of your motorhome chassis to their peak levels will help reduce fuel consumption and driver fatigue. This stands to reason; if you’re not continually fighting the steering wheel to keep the motorhome from wandering all over the highway, you’re not wasting fuel. Plus, you’re not wearing yourself out trying to anticipate the motorhome’s next move.
We don’t have the space here for a long discourse on how to maintain your shocks, align your wheels (an entire coach alignment, not just a front-end alignment), or maintain your ride height controls, but I can suggest you read the “Suspension & Steering Equipment” article in the November 2007 issue of Family Motor Coaching magazine, and the “Ride Regulators” story about shock absorbers in the July 2009 issue of FMC. You also can find these articles online at FMCA.com. Remember, if your motorhome is traveling straight down the highway, it’s using less fuel than a motorhome that bounces back and forth between the yellow lines.
Improve your coach’s airworthiness
A motorhome “” particularly a Type A coach “” pushes the air in front of it rather than slipping through it like a more aerodynamically designed Corvette. This column of air compresses and becomes more difficult to push as the speed of the vehicle increases. In addition to pushing air, a motorhome also pulls along a column of air that has less pressure than the ambient pressure on each side or above the coach. This column of air acts like an anchor, requiring additional power to “pull” the air along. Since more power requires more fuel, finding a way to eliminate this “drag” effect can reduce fuel consumption.
This column of air also is responsible for another problem motorhome drivers experience when being passed on the highway by a large vehicle such as a tractor trailer. When an 18-wheeler is about to pass a motorhome, it “pushes” against the trailing column of air with a slight sidewise shove. As this occurs the RV driver feels the front of the coach pulled toward the lane in which the truck is traveling, causing the driver to instinctively steer away from the truck. However, as the driver is making that correction, the front wind wave from the truck pushes the front of the coach away at the same time. The simultaneous wheel turn and push means the driver has to immediately correct the steering wheel again, this time back toward the lane the truck is in.
To help eliminate this anchor of air “” and the problems it causes “” I’ve found a device called an Airtab. A group of these small deflectors aligned along the rear edges of the motorhome break up the rear column of air with hundreds of little eddies, so there’s no “solid” air column being dragged along by the motorhome. There also is no air column for passing 18-wheelers to push against; therefore, the coach is much more stable around larger vehicles. Drivers will still experience being pushed away from the passing vehicle as it draws alongside, but this is easily countered. What you won’t have, however, is the multiplication of motion.
Since there’s no longer a low pressure area to pull on the motorhome, and the coach is more stable in traffic, a motorhome equipped with Airtabs should attain improved fuel mileage.
For more information about Airtabs, visit www.airtab.com or call (866) 758-4100. The product can be purchased from the company via the Web site or by calling (877) 604-2105. It also is available through Henderson’s Line-Up, Brake, and RV by calling (800) 245-8309.
Prior to installing the Airtabs, my motorhome’s engine would have to turn 2,000 rpm to reach 55 mph. With the Airtabs in place, 55 mph was achieved at just above 1,900 rpm.
Slow down!
The idea for this article came to me while on the way to a family funeral being held several hundred miles from my house. The distance was too great for the family to caravan and there were too many of us to fit into any one of our cars, so we decided to take the motorhome. One of my sons volunteered to drive. Not being accustomed to operating a motorhome, he drove it pretty much in the same manner as his six-cylinder pickup “” foot to the floor when the light turned green, passing slower vehicles, and maintaining the speed limit, whether it was 65 mph or 75 mph.
I know this is obvious, but sometimes it takes awhile for a driver to realize that a motorhome must be driven differently. Over hills and dales, around curves, and through swales, motorhome movement must be managed and controlled more carefully than a car “” no racing starts or abrupt stops. Maneuvers must be planned and then performed slowly. If not, safety can be compromised, fuel mileage will deteriorate, and the lifetimes of tires and chassis components will be reduced.
Driving more slowly makes sense for several reasons, but for this article we’re most concerned about fuel mileage. So, can you get significantly better mileage by reducing your highway speed? Good question, and since most folks probably do not have the time or patience to do multiple long-distance-driving test loops to determine at what speed optimum mileage is achieved, I’ve done it for you. While each motorhome and driver combination is unique, you can still use my figures as a gauge to help determine your own mileages at the different speeds, as the percentages should be pretty close and applicable to other motorhomes.
The test involved running a loop four times at three different speeds: 55 mph, 65 mph, and 75 mph. I drove the loop at 55 mph twice “” the first without the Airtabs and the second with the devices installed to determine whether they helped improve fuel mileage. The test was performed on a 94.5-mile closed loop on Interstate 40 (other than a block traveled from the fuel stop to the on-ramp and the turn-around ramps) so that any traffic changes would not have to be considered.
The coach used for this mileage test was a 1999 Tiffin Allegro Type A gas-powered motorhome on a P-Series chassis with a 15,000-pound GVWR. It has a 454-cid (7.4-liter) V-8 engine that is capable of 290 horsepower at 4,000 rpm and 410 pound-feet of torque at 3,200 rpm. It also is equipped with a four-speed automatic transmission, and it has approximately 23,000 miles on the odometer. The front and rear end caps measure 75.21 square feet each (the height from the ground times the width “” not including the mirrors).
I weighed the coach before each test loop. Onboard we had approximately 550 pounds of passengers (people and dogs), almost a full water tank, and empty holding tanks. The motorhome tipped the Cat scales at 13,500 pounds, leaving the coach with another 1,500 pounds of carrying capacity.
Once I was on the freeway, I set the cruise control to the speed for that particular loop (to assure consistency) and I verified the coach’s speedometer readings with my GPS readout. The cruise control on my motorhome can be precisely adjusted up or down, one mile per hour at a time with its coast (slower) and resume (faster) buttons. The dash air-conditioning was not used. This loop started at 3,500 feet and climbed to a maximum height of 5,200 feet (a normally aspirated gasoline engine loses effectiveness at approximately 3 percent per 1,000 feet in altitude, so you can use this altitude in your own comparisons).
Living in the desert, I’ve had to learn to deal with the wind, because, other than heat, it’s really the only weather change we go through. So I had to wait for calm days to do the test. This resulted in the runs taking place weeks apart (our first two loops were on January 2; our last loop was in March). When we finally looked out to see the flags hanging on their poles like limp laundry, we made our first two runs. With XM on the radio; a travel mug of fresh, hot Pilot Rain Forest blend in the cup holder; and a Kit Kat on my lips, we headed east out of Kingman, Arizona, on our 75-mph loop.
While I knew beforehand that there would be differences in the miles-per-gallon results from the three different speeds, I had no idea that the differences would be as great as they proved to be. At 75 mph, the Allegro achieved 7.89 mpg. The 65-mph loop produced 9.86 mpg, and the first 55-mph circle gave us 11.50 mpg. After installing the Airtabs, the Allegro produced its best mileage, topping out at 12.03 mpg at 55 mph.
As you can see, driving 55 mph provides the best fuel economy. And with the addition of the Airtabs, the numbers are even better. Now let’s put these results into a real-world situation. Driving 55 mph with Airtabs installed, I could expect to travel 1,203 miles on 100 gallons of fuel. The same 100 gallons would take me only 789 miles were I to travel the entire time at 75 mph. By slowing down and adding the aerodynamic helpers, the fuel mileage increased significantly.
Another piece of fuel-saving advice: Avoid driving in adverse weather conditions, as this can affect your mileage more than your driving habits. Traveling in wind, rain, etc. also will affect the driver and any passengers, because of the added stress. If you have the time, kick back and wait for better weather.
In conclusion
For those with Internet access, you can find up-to-date fuel prices at MapQuest’s Web site (www.mapquest.com). If you input your destination or the names of towns you’ll be passing through when you think your fuel gauge will be hovering around a quarter tank, MapQuest lists the fuel stops with prices, allowing you to pick the least expensive, and giving you one more way to save cruising cash.
In addition to MapQuest, you’ll want to check out some of the technical topics found on FMCA.com’s Community forum. One of the forums deals with fuel mileage and you’ll find many suggestions in this ongoing discussion, with new comments posted almost daily. One excellent suggestion was to visit Caterpillar’s Web site at http://ohe.cat.com/cda/files/287140/7/LEGT5364.pdf and read “Understanding Coach/RV Performance,” which was written for Cat power plants but applies equally well to other engines. This well-written pamphlet includes tables, charts, and many examples to explain its points.
If you would like more information about RV safety, weight, and tires, attend the applicable seminars at FMCA conventions and area rallies; or purchase a copy of RVSEF’s RV Safety Training Program, which features topics such as Towing, Personal Safety, Weight, Tires, Propane, Fire, Driving, Electrical, and Motor Fuels, and includes an excellent video as well. The program is available from RVSEF at www.rvsafety.com (321-453-7673) and also is sold at the company’s booth during FMCA conventions.
Driving Loop Results
Speed MPG
75 mph 7.89 mpg
65 mph 9.86 mpg
55 mph (without Airtabs) 11.50 mpg
55 mph (with Airtabs) 12.03 mpg