I just returned from the Pennsylvania trade/public RV show and while looking at a new motorhome on a Freightliner Custom Chassis I noticed what looked to be a small fuel tank located under one of the outside storage compartment doors. The cap on the tank had the letters (DEF) which I later discovered stands for Diesel Exhaust Fluid. I had no idea what Diesel Exhaust Fluid was, so I headed over to the Freightliner display to find out. The Freightliner representative was extremely knowledgeable and helpful in explaining what DEF was, and after returning home I decided to research it a bit further.
There’s no question that fuel economy is at the top of every RVer’s list, so in the next few posts, I’m going to talk a little bit about ways to improve fuel economy. I’m not speaking of the typical suggestions, such as driving 55 mph or slower or monitoring tire pressure (although those do help), I’m talking about ways to reduce resistance overall. Reducing resistance improves efficiency, and that means better fuel economy.
Obviously, tire inflation pressure is important, but so is the type of tire that you use on your coach. A tire that is wider than necessary typically produces a better ride, but it can also increase rolling resistance. That’s why a lot of truckers are going to what is called a “super single” on the rear of their trailers; instead of duals, they run one very heavy-rated tire and wheel per side. Our shop hasn’t experimented with this, and the motorhome industry hasn’t introduced super singles yet, but it could come to that. A narrower, heavy-duty tire will ride rougher than its wide, cushy counterpart, so you’ll have to ask yourself if you’re willing to sacrifice a little bit of comfort for improved fuel economy. I should note here that a larger diameter tire won’t hurt fuel economy and may even help it, because a larger diameter tire turns fewer revolutions to cover the same distance and engine rpm is lowered as a result.
Alignment is also extremely important. This is a pretty broad subject, which is why we’re not going to try to cover it all in one post. Incorrect alignment can cause a lot of resistance, requiring more throttle input to maintain a given speed. “Toe in” is the most critical setting of them all. Simply put, “toe in” means the front of the tires are “pigeon toed”. Obviously, too much toe will also cause your tires to wear more quickly. Here’s a little graphic of what toe in/toe out looks like:
It’s a good idea to have the alignment checked even when the coach is new, because the factory runs them through the alignment procedure pretty fast. And, when the coach is loaded for travel, especially an independent front suspension (IFS) coach, the alignment changes as the load changes, except on self-leveling, air suspension coaches, where correct ride height is constantly maintained.