May 18, 2006
Driving Tips - What Really Saves Gas? And How Much?
[ adapted from = edmunds ]
With gas prices so high, the media is awash with lists of gas-saving tips. Well how's this for a tip? If you listen to us, you can see hybrid-type savings without having to buy a new car.
By changing your driving habits you can improve fuel economy up to 37 percent right away (depending on how you drive). Combine several tips and perform routine maintenance and you will save real dollars, not just pennies.
A miracle? All we did was take several of the most common tips out there and put them to the test over a remote 55-mile route in the high desert of California. Some of them worked like a charm. Some of them didn't work at all. We'll give you the breakdown.
These tests were done under real-world conditions — not in a government lab somewhere. Our results can be matched by anyone — even you.
The wonderful part about what we found is that improving your car's mileage is just a matter of changing your habits. Stack a few of these winners together and we'll bet that you'll see a substantial savings at the pump — without the need for a new car.
Our results are based on two separate fuel testing sessions. On each occasion we took two cars from the long-term fleet and drove on a 56-mile test loop. Our route circled Owens Lake near Lone Pine, California, at the foot of Mount Whitney, the tallest mountain in the lower 48 states. We chose the route because it was so deserted we could vary our speed and driving style without interfering with the flow of traffic. The only other cars we saw on the route were a caravan of test vehicles from Mercedes-Benz. We drove the loops back-to-back to ensure that we were comparing similar wind and temperatures. We logged our results and later put them on a spreadsheet where the results were averaged.
Test #1: Aggressive vs. Moderate Driving
This is gonna hurt. Our tests showed that the most significant way to save gas is: you. And we're talking massive fuel economy gains. Think you need a hybrid? Chances are you've got hybrid-style mileage in your gas pedal foot. Don't mash the gas when you start up. Take the long view of the road and brake easy. This tip alone can save you unbelievable amounts of gas. If you slowed your 0-to-60-mph acceleration time down from your current 10 seconds to a more normal city pace of 15 seconds, you'll feel the savings immediately.
Method: We conducted this test four times. The first time we did the full 55-mile loop once by accelerating aggressively 15 times at 3/4-throttle from zero to a cruising speed of 75 mph. We also applied the brakes hard to come to a full stop. Then, we drove the second loop by accelerating moderately 15 times at 1/4-throttle to a cruising speed of 70 mph. We braked lightly to a full stop. In the second set of tests we drove 25 miles making 25 rapid accelerations to 65 mph at 3/4-throttle. After 1 minute of cruising we braked hard and repeated the cycle up to 65 mph. We then drove the same distance making 25 moderation accelerations to 60 mph at 1/4-throttle. After 1 minute of cruising we applied the brakes easily and came to a full stop.
Test #2 Lower Speeds Saves Gas
Remember a thing called the speed limit? On most highways it is either 65 or 70 mph. How fast are the cars and trucks around you going? From 75 mph to 90 mph. These people are wasting a lot of gas for the chance to get there a little earlier. Factor in safety concerns and a speeding ticket once or twice a year and going fast is a costly proposition.
Method: This test was simple. For 50 miles we drove with the cruise control set at 65 mph. Then, for another 50-mile stretch we drove with cruise set at 75 mph. We repeated this test going in the opposite direction. It is amazing how obvious the difference in gas mileage was. Just think what would have happened if we had slowed down to 60 mph. The only problem is with impatient drivers behind you. One driver became so irate that he tried to run our editor off the road. Still, if you are pinched by gas prices. Leave a little early and drive the speed limit (in the slow lane).
Test #3 Use Cruise Control
Using cruise control is a bit of gas-saving advice frequently on tips lists. We have always agreed with this tip in theory but we hadn't expected such significant results. First, it smoothes out the driver's accelerator input by preventing nervous "surging." Second, it makes the driver take the long view of the road rather than reacting to every change in the traffic around them.
Method: We did this test twice with four different cars each time driving the 55-mile loop. The first time we set cruise control to 70 mph. The second time, with the cruise control off, we varied our speed between 65 mph and 75 mph. We tried to mimic the driving style of a person who is in moderate freeway traffic.
One thing that's important to note: if you are in a mountainous area you should turn off cruise. It will try to keep you up to the speed you've set and will use a lot of extra gas downshifting to lower gears to accomplish this.
Test #4 A/C On, Windows Up vs. A/C Off, Windows Down
This has got to take you back to the days with the family on vacation. Dad says, "Turn the A/C off! It wastes gas!" And Mom says, "We can't roll the windows down or everyone on the highway will think we can't afford A/C." And you're in the back roasting, hoping someone will win the argument so you can cool off.
Well, family psychology aside, if dads are still saying this, they aren't necessarily right. While the A/C compressor does pull power from the engine wasting some gas, the effect appears to be fairly minimal in modern cars. And putting the windows down tends to increase drag on most cars, canceling out any measurable gain from turning the A/C off. But this one depends on the model you're driving. When we opened the sunroof in our SUV, the mileage did decrease even with the A/C off. Still, in our experience, it's not worth the argument because you won't save a lot of gas either way. So just do what's comfortable.
Method: We drove the full 55 mile-loop in two cars at equal speeds both times — 65 mph. The first loop we drove with the A/C on and the windows up. The second loop we drove with the A/C off and windows down. In the second test we drove 20-mile loops. This was far enough to see our gas mileage level off and remain steady on the computer trip meter.
Test #5: Check Your Tire Pressure
No matter how many times drivers hear about the importance of tire pressure, most of them don't do anything about it. They probably don't like squatting beside their car in a busy gas station with fumes swirling around them. But is it important? The answer is yes, for a number of reasons. Properly inflated tires are less likely to fail at high speeds. They wear more evenly and, yes, they deliver better gas mileage. How much? In this test we saw a modest difference in two of the cars. It might have been more dramatic with different tires on different cars. Experts swear by it; we couldn't really document it. And we wound up wondering if tire technology, like the design in other areas of the car, had improved.
Eventually, we concluded that each set of tires is different and every vehicle is different. We recommend that you do your own tests to see what inflation setting gives you the best fuel economy.
Method: We drove the 55-mile test loop four times at 60 mph — twice with tires at or above proper inflation. Once, we did the test with the tires 5 psi below the pressure recommended by the manufacturer. Since this produced very little difference we enlarged the gap and under inflated the tires by 8 psi. We felt that it was important to make sure the tires were inflated to the recommended level or above.
Test #6 Avoid Excessive Idling
If you turn off a light bulb as you leave the room you'll save electricity. If you turn off your car you will save gas. Obviously. But related questions are more difficult to answer. If you're only stopping for only a minute, is it better to shut off the engine or keep it idling? Should I shut off the engine in traffic? How much gas will this save? What rule of thumb do I use when trying to save gas this way?
Method: We took two cars and drove a 10-mile route stopping 10 times for two minutes. We shut down the car each time. Then we drove the same route at the same speed and let the car idle for two minutes.
The good news is that you can drastically improve your gas mileage. The caveat is that you have to change your driving habits. If you are willing to change, you'll find many related benefits too: no speeding tickets, greater safety, reduced stress and lower repair bills for tires and brake pads. In the long run this will save you money. And who knows? You might like the new you.
Posted by Steven Wong at 6:47 PM