Top Ten MPG Tips

Oct. 19, 2008 By Craig Perronne

The good news is gas prices are down from the horrifying highs we saw just a couple months ago. The bad news is now we are all broke, or about to be, from this lovely financial crisis. While gas is cheaper, it can still be a significant part of our budgets for those of us who tow or use our trucks to shuttle our toys. With our rigs not getting that great of fuel economy to start with even small improvements can make a significant difference in spending over the course of a year. One should not also expect gas prices to stay down for long as OPEC is already planning to slash production in an effort to raise prices back up. So instead of telling little Jimmy he won’t be able to go to college, save some money by following our top ten gas saving tips.

Just because your vehicle is built to go fast doesn't mean you have to. Even slowing down a bit can yield a decent improvement in gas mileage.

Slow Down
In our fast-paced lifestyle the majority of us are guilty of driving at above legal speeds. For whatever reason we feel like we need to be wherever we are going as quickly as humanly possible. Here in the mess of freeways that is Southern California 80 mph is the norm. If you are in the carpool lane, 110 mph is advisable to keep the jackass behind you from riding your bumper and flashing his brights.

While shaving a couple minutes off your trip might allow you to arrive home just in time to catch Joe Dirt on TBS for the 27th time, it is also costing you money. This is because drag does not increase in a 1:1 ratio with speed but rather increases exponentially. To be exact drag increases with the square of speed meaning even a small reduction in speed can be beneficial. The difference between 80 and 70 mph can result in a decent bump in MPG.

Trucks are not known for their aerodynamics but engineers are now beginning to closely look at ways to improve aerodynamics to help increase gas mileage.

Aerodynamics
The aerodynamics of a vehicle play a major role in determining its gas mileage. About 60% of the power required to cruise at highway speeds is taken up overcoming air drag. With drag increasing exponentially, this figure can increase quickly at even slightly higher speeds.

A figure often quoted in aerodynamics is drag area which is the product of a cross-sectional area of the vehicle and its drag coefficient. An average full-size car has a drag area of roughly 8.5 feet squared. The Honda Insight is one of the most aerodynamic cars produced (and not surprisingly one of the most fuel efficient) and has a drag area of 5.1 feet squared. On the opposite end of the spectrum is a Hummer H2 with a drag area of a whopping 26.3 feet squared.

Obviously our vehicles are very aerodynamically challenged to say the least. However it is not completely hopeless. While that roof rack with a bunch of lights hanging on it might look cool, it is cutting through lots of air perched atop your rig. A huge front bumper with a bunch of lights, big towing mirrors and tires sticking way outside of fenders can also have a negative affect on aerodynamics. While some of these are just part of what we do, others do not have to be on the vehicle all the time and can be put in place only when needed. Paying attention to the aerodynamics of your vehicle can yield a slight bump in mileage.

Rolling Resistance
Rolling resistance is exactly what it sounds like and is the resistance that occurs when round object (in our case tires) rolls on a flat surface. About 5-15% of the fuel consumed by a car can be attributed to rolling resistance. Obviously with the big, aggressive tires we tend to run that number can be much higher.

Tread patterns can be a big factor in rolling resistance. Large voids with big tread blocks, such as those found on aggressive mud tires, tend to dramatically increase resistance. Tire width can also play a role as the wider a tire is the more contact area it has making it harder to roll.

Obviously this advice has to be put into the proper context. If you have a dedicated trail rig there is no way you are going to remove your aggressive trail tires for some milder ones and it is doubtful you care about mileage. However if you have a tow rig or a 4x4 that serves double duty as a daily driver as well, you might want to take a look at its tires. If you can’t remember the last time your mud terrains saw mud then switching to a milder tread pattern could net you some more MPG.

The heavier the tire, the more power it takes to turn and fuel economy suffers.

Tire Weight
Tire weight is also closely tied to rolling resistance. Heavy tires take more power to get spinning and keep in motion. Obviously a 44-inch Super Swamper is harder to get moving from a dead stop than a 33-inch all terrain tire. The more power needed to keep a tire moving, the worse the gas mileage.

Wheels are often overlooked but a heavy wheel is just as bad as a heavy tire. You want to look at the overall weight of the wheel and tire combination and not just one piece of it. Huge wheels, beadlocks and heavy designs can sap fuel economy as well. Running the lightest tire and wheel combo possible will help to increase your MPG. Your brakes and suspension will also thank you.

Proper Inflation
By now everyone should know due to all those commercials with Mario Andretti that keeping your tires properly inflated is important. While Mario is more concerned that your tires don’t blow out and you sue a particular tire company, under inflated tires can also have a negative impact on fuel economy. When it comes to the large tires we run, not having them properly inflated can have even more impact. Airing down is a common practice for any of us hitting the trail as it makes for a much smoother ride. Lower pressure in a tire also allows for a much bigger contact patch greatly increasing traction. However that bigger contact patch on the highway leads to greatly increased rolling resistance. Make sure to air up your tires and keep them aired up way beyond trail pressures to minimize resistance. Remember all tires list their maximum tire pressure on the sidewall and that air expands so do not fill them to this maximum.

Overall vehicle weight also has an impact on gas mileage. The heavier a vehicle is the more power it takes to keep it moving.

Weight
Lotus founder Colin Chapman lived by the idea that weight is the enemy of performance. By the capabilities of his sports cars it is easy to see he is right. However weight is also the enemy of gas mileage. Just like a heavy tire, a portly vehicle takes more energy to move. The heavier it is the less the gas mileage as it is simple physics.

By nature four-wheel drives are heavy vehicles. Big tires, heavy axles, transfer cases and stout frames all add pounds onto a vehicle. Even though our vehicles are oversize, some dieting can shed some pounds. Extremely heavy winch bumpers, carrying a full array of spares and tools all the time, spare tires and other add ons can quickly pile on a lot of weight to a vehicle. Paying careful attention to these items before purchasing and making sure to remove those that are not always needed (such as spare tools) can help trim down your overweight vehicle.

Leaving a stoplight in a manner such as this can have a very negative impact on gas mileage.

Hard Acceleration
It should come as no shock that accelerating hard from every light and stop sign can put a significant dent in fuel economy. Obviously the more liberal you are with the gas pedal, the less your miles per gallon will be. If you are trying to maximize fuel economy envision that there is an egg under your gas pedal and drive accordingly.

Air Cleaner
Your vehicle’s air cleaner is vital to engine performance. The dirtier it is, the harder it is for the engine to breath. As an engine’s efficiency goes down, so does its fuel economy. If you have a stock air cleaner make sure it as clean as possible and don’t skimp on replacing it if needed. Upgrading to an aftermarket air cleaner is also a worthwhile investment as the much better flow they provide over a stock filter can help increase MPG along with their better filtration qualities.

Tune-up
An efficient engine is an economical one and a clean air filter is only the start. Every other part of your engine should be in excellent condition as well. Make sure that your spark plugs, coils, distributor and the rest of your ignition system are functioning properly and replace any items needed. Oil and coolant also need to be at their proper levels and in good condition for your engine to be happy. If has been awhile since you have given your engine a proper tune-up your gas mileage may be suffering.

Gearing
Putting larger tires on our rigs is one of the most common modifications we do. However not changing the ring and pinion ratio to match larger tires is another way to decrease fuel economy. While reducing engine revolutions at speed can sometimes be beneficial, there is a fine line where the engine is being lugged and needs more fuel to maintain forward momentum. If you need more throttle to keep your larger tires moving chances are good your gas mileage is going down even if your rpm’s are reduced. Got tips and a truck to show off? Log on to My.Off-Road and share the love!

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