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Factors affecting fuel economy

In this era of high gas prices and dependence on foreign oil this is more imporatant than ever. What are most important action affecting fuel economy that drivers of existing vehicles can take other than buying newer vehicle? Especially interested if reducing extra weight from things like bike/boat roof and hitched racks, heavy tool chests, camping equipment etc. effect fuel economy in any measurable way. I know tire health and pressure, driving habits and regular maintenance are probably bigger but I’ve been told weight is insignificant.

I don’t know who said it, but along with good driving habits, weight is very significant, along with aerodynamics. A light car, even with a large motor, can get excellent mleage if driven conservatively.

If you are stuck with an existing vehicle, THE single most significant factor is driving style. Slow and gentle - compared to hard and fast - will pay large dividends. The key is to avoid using the brakes. Brakes just get rid of energy - transforming velocity into heat. When approaching a stop light, letting off the gas early, instead of waiting to the last moment to apply the brakes, preserves the energy.

But weight does have an effect, but it’s hard to significantly reduce the weight of a 2 ton vehicle. Don’t carry around a lot of useless stuff.

Also, careful selection of tires has some benefits. In tires, Rolling Resistance, Traction, and Treadwear are tradeoffs. If you want to maximize one of those 3 properties, you have to sacrifice one of the other properties (or both!). Time spent in the tire buying process can pay long term benefits.

Remove the roof rack. In addition to the weight, it’s a HUGE aerodynamic drag.

Basically a worst-case scenario: It’s a “bluff body,” protruding directly into the airstream, in a location where the air likely flows at a velocity in excess of the surrounding airstream.

P.S. Lowering weight generally affects “city” MPG most; lowering aero drag affects “highway” MPG most.

Well I added a supercharger to my daily driver, but it didn’t increase fuel economy. I also had 4.10 gears put in the car as well, that did increase city mileage somewhat, since it’s now possible to drive in 5th gear at 35 MPH and not lug the engine. Previously I would’ve had to drive most of my commute in 4th gear at around 2000 RPM, now I can drive the same route in 5th gear at 1100 RPM, Huzzah!

I added a 4 inch lift, larger tires and 4.56 gears to my Bronco, that certainly didn’t increase the fuel economy.

Gas is still pretty cheap all things considered.

If you cannot “upgrade” to a more fuel-efficient vehicle, then all you can do is–

Maintain the car flawlessly.

Keep your tires inflated to a few lbs over the tire pressure recommended by the vehicle manufacturer (no more than 5 lbs additional, or you risk impairing the car’s handling qualities in extreme situations!)

Drive as if there was a raw egg in its shell between your foot and the pedals. In other words, only use slow and gentle pressure on both gas and brake pedals.

Reduce all unnecessary extra weight in the car.

DO NOT “warm up” the engine for more than a few seconds.

DO NOT use drive-up windows at banks and fast food joints.

DO NOT tailgate other drivers. Tailgaters must use the brake more frequently than those who leave an adequate distance behind the car in front of them. Every time that you brake, you lose energy and must also apply more gas to compensate for slowing down. If you leave a space of 2 car lengths for every 10 mph of speed, you will be able to drastically reduce the amount of braking that you do.

Make sure that you are using the octane grade of gasoline that the vehicle requires. Using the wrong octane can reduce your fuel economy.

One thing I focus on is speed. I will probably get beat up over this, but it is legal to drive 65 MPH where the speed limit is 70 MPH, and if you use cruise control at the same time, driving 65 MPH will probably save you more fuel than just about anything else mentioned here so far. I usually only do this when I am towing freight or driving a large RV, but if you do this, make sure you stay in the slow lane. You won?t pass many vehicles going this speed, but when you do, make sure to get back over to the slow lane ASAP.

One of the biggest fuel savers of hybrids is their ability to shut down at red lights. You don’t want to wear out your starter, but when you have to stop at a train crossing, or have another long wait, shut off your engine ASAP. There’s usually no reason to wait to shut down your engine.

Bike racks, ski racks, and roof storage boxes create a lot of extra wind drag and resistance. Take them off when not needed.

Reduce weight, you might not see a big difference tank per tank, but over time extra weight reduces fuel efficiency. If you have heavy 3rd rows of seats that are never used take them out and store them. Remove excess stuff from the trunk you don’t need.

Slow down, reducing cruising speed on the highway from 75 to 65 will make a measurable improvement in your mpg. Reducing speed 5% increases fuel economy 20%.

Smooth and steady starts help mpg. Accelerating smoothly uses the transmission gears effectively. You want to get into top gear without pushing down too much on the gas petal.

On hilly terrain I turn the cruise control off. I let the car roll downhill and take some extra momentum into the uphill grades. Truck drivers use the technique to maintain speed as well as reduce fuel use.

In this era of high gas prices and dependence on foreign oil this is more important than ever.

I know this statement has little to do with the actual question but; I feel it’s like people trying to avoid foreign made cars. IT"S IMPOSSIBLE TO NOT CONSUME FOREIGN OIL and we shouldn’t try !!!
IMO, all oil goes on the the world market and deliveries are made much like the common pipelines within the US; by convenience. It’s cheaper to “import oil” from parts of Canada, the North Sea or even the Middle East to different refineries than extract it from more deep sea wells in the Gulf or from Alaska. Without foreign oil, the prices would be much higher. I may be nitpicking, but I feel the idea is not to be as dependent upon domestic oil and oil in general for basic transportation and use alternate energy sources for which the EV is an ideal “vehicle”.

I think oil is more valuable for long haul, construction, defense and aviation and easy access Middle East oil is important for that strategy and it’s as if not more important that these areas become more efficient than cars. Avoiding air travel and taking high speed electric rail might accomplish this goal more than any debate about stream lining an SUV.

So let’s just say “dependency upon oil” or just making it cheaper for us to operate the cars we’re stuck with now.
Sorry for going off topic…continue.

If you drive a lot of open highway, you can always drive behind the tractor trailers.
Don’t tail gate them, just drive behind them.

The bit of slip stream you get into will increase your fuel economy a bit.
Also, they tend to travel at or just below the speed limit, which will allow you to save even more fuel.


First do the brick mod. That is drive as if there was a brick under the accelerator. You likely will be surprised how much of a difference that can make.

We have a newer car with an average and instant gas mileage readout. Zeroing the average mileage meter while driving at 60 mph (65 limit) results in a nice mpg number, better than the EPA figure. That number is brought down significantly with low speed traffic conditions with stoplights etc. Driving in a rainstorm or on slushy roads are detrimental to gas mileage as are bumpy roads. A few days ago we were getting a much worse average mileage while fighting a headwind.

It may not be possible to avoid these conditions but if you can, there is something for your gas mileage.

Numbers don’t always matter when it comes to true fuel economy. Fewer drives is a great way to save. Learning how to cook would have saved me some bachelor money but there were these great restaurants in Caribou Me. at the time.

The waitresses thought I sat there reading Playboy Magazine. For the record, it was Forbes. Didn’t do a lot of good, I’m still not rich.

Is it speed or rpm’s that matter? For instance, if you’re at the top (rpmwise) of a gear at 55 mph and at the bottom of a gear at 60, wouldn’t going 60 be better?

Yup, the Z06 Corvette is a good example. 7L v8, 505 hp, 3175 lbs, 24 mpg highway.

55 MPH would be better. The drag force increases with the square of the velocity.

You also can’t just look at the RMP vs Speed for optimum fueling. The load of the engine, or the amount of air the engine is consuming, is what determines the amount of fuel burned.

Everything mentioned so far is important. Depending on circumstance some things are more important than others.

Unless you own a hybrid all of the fuel burned to move the vehicle is lost to heat when it comes to a stop. It doesn?t matter if you coast to a stop, brake to a stop or hit a pile of sand. Obviously, any extra weight you lug up a hill will cost something in fuel.

The power required to accelerate a car is a square function. Doubling the acceleration requires four times the energy (2^2). Aerodynamic drag is a cube function. Doubling the speed requires eight times the power (2^3). A vehicle that needs 10hp to go 50mph will need 80hp to go 100mph.

ICEs are the most efficient at converting fuel to work when they are run close to full throttle at the engine?s torque peak.

If you live in Kansas aerodynamic drag might be more important than some extra weight. If you live in a city hard acceleration might be the thing to avoid. If you drive Interstates in the mountains it?s all significant.

The most effective but unpleasant thing you can do to economize is to drive less.

It bugs me to see only the highway fuel economy listed, especially in a discussion about vehicle weight, which has more effect in stop-and-go traffic that it does on highway driving.

It bugs me even more in the car commercials, where it is done deliberately to mislead people. Very few people do most of their driving on the highway.

“36 mpg highway and only $199 a month for 36 months for well qualified buyers”

Also, that Vette is rated for city about what I’m getting in my Mazda, with almost 1/3 the engine(7 vs 2.3L), and it weighs 900lbs more.

The next time you need new tires, shop for low rolling resistance tires. Michelin and Continental have them but there may be more by now.