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Car Corner
Practical Tips For Better Gas Mileage - Deceleration Management

April 1, 2007
By Scott Lewis

This month I am going to discuss gas mileage. I have talked about this subject before, but this will be different. I plan to cover in-depth ways to improve your gas mileage. Maybe I need to say that again... I plan to cover in-depth ways to improve your gas mileage.

Typical Improvements

Many times when you read an article on gas mileage, or in this case getting better mileage, you get bombarded with lots of information that really doesn't matter. For instance, keeping your tires properly inflated will help your car get the best mileage your car can get. But this does nothing to help you improve your gas mileage as a driver. After all, your car had properly inflated tires when you bought it (assuming you bought it new, and the dealer prepped the car correctly).

Anyone can tell you to keep your car properly tuned, tires properly inflated, oil changed regularly, filters replaced when necessary. Yes, clogged filters will reduce your car's gas mileage. So will a lot of other things. Heck, dirt on your car can reduce your car's gas mileage (it increases the drag on air over your car).

You know all these things:

  • Change your oil and filters regularly
  • Keep your car clean
  • Keep your tires properly inflated
  • Keep the junk out of the truck

As I said, all of these are in place when you buy a new car. They are clean, with clean filters and air in the tires. These will help your car get its best mileage but do nothing to help you get your best mileage. You know the old saying... your mileage will vary.

What I intend to cover is driving techniques that will help you improve your mileage. And just to show you that these techniques really work I am going to employ them in my own personal driving and show you the real world improvements.

The Route

When I started researching and writing this article I though I should find a good route to take to and from work. In the morning I have two main options and one minor option. I could head north on 281 and catch 46 east. I live in San Antonio and work in New Braunfels. I could also travel easy on 1604 and then north on 35. The "minor" option is when going north on 281 I can take 1863 and cut into 46 just as it hits New Braunfels. I like the drive up 1863. I am on it for over 20 miles and it is a nice leisurely drive through the lower part of the Texas Hill Country. The road winds and twists and goes up and down. It is relaxing. And some of my driving techniques work quite well in this environment.

Coming home is always the same... 35 South to 1604 West. 35 is 3-4 lanes each way (all mentions of lanes is just the number of lanes on the one side you travel), while 1604 is two lanes. 281 is also 2 lanes but 46 and 1863 are both one lane roads. One lane roads can be bad for the driving techniques I am going to show you, but not impossible. The real reason for the two possible paths in the morning are in getting to 281 or 1604. Traffic! Yes, there is traffic in San Antonio, Chip. The path to 1604 is very backed up and would not provide the best gas mileage. Going to 281 and heading north is better. However 1863 is under construction and you can get stuck sometimes. This is bad for mileage... just sitting in an idling car. 46 is not much better because of the inability to pass (legally & safely) that you could end up behind some slow poke (which actual could help your mileage as we will see).

So... should I go to 1604 and deal with traffic, but then run freely with two to 4 lanes? Or should I go to 281 and deal with 1 to 2 lanes the entire way?

Then it dawn on me. It doesn't make a difference which route I take. If I go north then east and get 2 mpg less than if I go east then north what does that prove. It proves that my car got that mileage on those routes. My driving techniques will work on any route, so all I have to do is pick one and stick to it for all my testing. The goal is to drive in the same traffic and roads day in and day out so the experiment is consistent.

I am going to take the 1604/35 route for the lanes.

Expected Improvement

You are probably thinking that I can't come up with driving techniques that will make a huge difference. That depend on your definition of "huge difference." Before I logged any miles for this experiment I took a guess and expected to see an improvement of 3-4 mpg. Is that significant enough? Remember, this is regardless of the route, traffic, etc. How well did I actually do? Read on and we will get to that.

As a baseline I drove to and from work for one week using no techniques. I set my car's on-board computer to display the temperature (you'll understand in a minute) and just drove to work for five days in a row. Driving without paying any attention to gas mileage resulted in an average mileage of 26.1 mpg.

Before we get to the driving techniques we need to cover the equipment I used, and what you will need to get the same results as I did. Remember, you should see the same improvement as I from a percentage standpoint.

Equipment

Yes, there is a catch to this "gas mileage improvement for nothing." You will need two pieces of equipment to match the mileage improvement I got. Granted, you can still do it without the equipment, it's just that these two items make it MUCH easier to get there. So, what are the two magic pieces of equipment that will ENABLE you to get YOUR best mileage?

1) On board computer with instantaneous and average mileage readings.
2) Manual transmission.

It's that simple. Granted the manual transmission is a stretch for some people. Some cars just don't come with manuals anymore. Most of the techniques below will still work with an automatic, it's just a lot easier with a manual.

If your car does not have a computer readout for mileage make sure you get one in your next car. They work. And they can be the key to following some of the techniques below. I used the on board computer on my Mini Cooper for all the mileage amounts stated in this article.

Deceleration Management

It's time to get into the nitty gritty. Deceleration Management is a term I came up with. Basically everything below is about NOT slowing down... or slowing down as slow as possible. It is not the slowing down that impacts your mileage. It is the acceleration you have to do after you slow down that impacts mileage. If you don't slow down you don't have to waste gas speeding up. Simple. Or simply stated... deceleration management. Neat term, Huh?

Technique #1 - Use your instantaneous mileage reading to get rid of that lead foot. That's right, all we are doing is paying attention to the mileage the car is getting. I believe that this consciousness of your mileage will help you drive better. I find it amazing how easily people drive with a heavy foot... for no reason. If you are unsure if you are pressing too hard on the throttle look down at the mileage readout and lighten up on the pedal. I can't tell you how many times I can look down at the readout and see I am getting 25 mpg on the highway. I will lift up and drive with a light food and the constant mileage with jump up to 28-32 depending on how heavy I was. Tailgating is the number one reason for this. If you are constantly riding the person in front of you waiting to jump into another lane you are wasting mileage. It is not the person in front of you that is the concern, but the people around you that are preventing you from driving faster. That's right... the people around you. The car in front of you is the reason you want to leave the lane. Fine, leave the lane, but don't get caught up in tailgating. That does not get you anywhere. Lighten up on the throttle and leave a few extra feet between you and the slow-poke. Then when you see an opening take it and get back to normal driving.

I used this technique alone and saw my average mileage for one week go up to 28.6 mpg. However, there is a little something to that number. It turned out that the week I drove with this technique was a light week for traffic. School let out for the Christmas break, and I had a much easier drive to work. My mileage was up to 29.0 at the middle of the week. I firmly believe I would have gotten 28.3 or 28.0 mpg had the traffic pattern been the same all week long. (Note: this is the problem with real world testing... you get real world results that may not be 100% consistent.)

That's an improvement of 9.6% just for watching that constant mileage readout and making sure I was not using more throttle than necessary for the situation at hand. Simple but effective.

Technique #2 - Gravity is your friend. This can be the best tip if the roads you drive on let you work it to the maximum. Basically you are going to make sure you are INCREASING your speed going down hill and letting your car decrease in speed going up hill. Simple, right. The real trick is to drive as smoothly as possible. The ideal situation would be to have a throttle that worked like those in boats. You know, just set the engine at a constant speed and let the load do the work. For us we will be using that light foot you developed in step #1.

If you take this to the extreme you can piss off a lot of traffic. You probably don't want to let your car slow 20 mph going up a hill. But it is the idea we are after. Let the car slow down going up a hill. You will get that speed back when you go down the other side of a hill. More importantly, if you see you are going down hill and there is an uphill ahead you want to make sure you gain as much speed as possible so you have the extra speed to lose when you head uphill.

Use the constant fuel mileage readout to help you determine how fast or slow to go. Just keep your constant mileage as high as you can without slowing too much on those uphill runs. I like to keep my car to within 10 mph of the speed limit. If I am on a highway with a 70 mph limit I make sure I don't go below 60 mph and stay below 80 mph. You have to make the most of every downhill. Even if it means accelerating ever so gently for as much as you can. This is the heart of Deceleration Management. Minimizing deceleration by using gravity where it helps you most.

By using this technique I was able to further improve my mileage to 29.4 mpg. Now, you may be saying that this is not that much of an improvement over the last steps 28.6 mpg. After all, that's only an improvement of 0.8 mpg. Well, I have another story. On Tuesday morning of the week I used this technique I got stuck in a really bad traffic jam. I have not yet introduced a technique to handle this. I watched my average mileage rise every day that week and I hit 29.4 on Friday afternoon. I believe if that Tuesday morning had been a normal day I would have hit 29.7 mpg for the week (the next increment on my computer's read out). So far we have improved our mileage by 12.6% from our baseline. Keep in mind that I thought I would get less than 28.6 with technique #2. I really think technique two would be good for more than 1 mpg improvement. But dealing with traffic (yes, as little as it is) is part of the problem. Our next technique deals directly with traffic.

Technique #3 - Neutral is your best friend. If gravity is your friend then neutral is your best friend. Never use your engine to slow your car down. If you are completely off the throttle you should be in neutral. What? Listen... if you are not using the gas pedal then your car's engine is helping to slow you down. This is called engine braking. It is minimal with automatic transmissions because of the slippage they experience. However, with a manual transmission it is more pronounced. Shift into neutral as soon as you can. Going down a long hill that does not have an uphill on the other side means you should be coasting in neutral. When you see a traffic light up ahead that you will have to stop at you should be in neutral. Get into neutral as soon as you can. Who cares if the guy behind you doesn't like how you coast up to a red light. Is he paying your gas bill. I will shift into neutral anytime I can. The best time is when I am leaving the highway. I almost always will hit a traffic light so I pop it in neutral while in the exist lane of the highway. I don't even wait to hit the access road.

Using neutral is also our main traffic technique. There are two kinds of traffic in my opinion. Stop and Go traffic, and very slow moving traffic. The idea here is to give the car a quick burst and then pop it into neutral and coast. When I am stuck in bumper to bumper traffic I will give the car a quick release of the clutch in first gear then coast in neutral for as long as I can. "As long as I can" usually means "so long as I don't piss the guy off behind me." Change the rules of the game. Instead of stop and go it is burst and coast.

For really slow moving traffic I use idle. Yes idle. My car idles at 5 mph in 1st gear, 8 mph in second gear and 11 mph in 3rd gear. 4th and 5th were a little too hard to pin down, but I was able to check that I idled in 6th gear at 18 mph. However, 4th through 6th will only work on perfectly flat or slightly downhill road. Non of those gears will maintain speed on any kind of uphill grade. Anyway, if traffic is moving at less than 20 mph you should try idling as much as possible. When traffic slows you go back to using neutral.

By using these two techniques to battle my traffic situations I was able to average 30.5 mpg, but this was only over 4 days. I was at 30.5 from Tuesday to Friday morning. There is no reason I see that I would not have finished the week with 30.5 mpg, except I was in a serious hurry coming home Friday and blew off all the techniques. Hey, I was meeting my wife and kids for happy hour.

Technique #4, #5, #6, #7 and #8 - At this late stage we are getting diminishing returns on our investments. Keep in mind that I am getting 30.5 mpg with a car that is EPA rated at 32 mpg on the highway. I am doing mixed driving, and dealing with about 3 miles of bumper to bumper traffic each day. I cannot work miracles. So for this fourth round we are just going to pull out all the stops. Can we break 31 mpg? We'll see.

Technique #4 - No Braking. If gravity is your friend, and neutral is your best friend then brakes are your enemy. Remember, we are dealing with Deceleration Management. Deceleration Management means slow down as little as possible. Brakes are such a waste. Every time you touch the brake pedal you are throwing mileage out the window (unless you are driving a hybrid that uses regenerative braking). You need to look further down the road and anticipate the need to slow down and shift into neutral as soon as possible.

Technique #5 - Faster Cornering. This is really an extension of #4. Don't slow down for turns, exits and off ramps. To stay off the brakes we want to take those off ramps and clover leaf exits with as much speed as possible. Slow down as little as possible. This is were having a good handling car can come into play. Take that side street turn at 25 mph. Why slow down to 10 and have to use gas to get back up to 30.

Technique #6 - Super Slow Acceleration. This is where you will watch your constant mileage readout and keep it above the highway mileage rating for your car yet still let your car accelerate. On level road I can be increasing my speed by 1 mph in a 1/4 mile. If a hill is one mile ahead I can use that distance to increase my speed by 4 mph. That's 4 mph I can let slide by going up that hill. Better to get 35 mpg while gain some speed now then 25 mpg while trying to keep from losing speed later. This one is probably the hardest to perform.

Technique #7 - Skip Shift. Chevrolet puts a device into manual Corvettes that will force the transmission to shift from 1st to 4th. It is called Skip Shift. If you are light on the throttle in first gear your will be forced into 4th. My Mini Cooper does not have the low rpm torque to support shifting from 1st to 4th. However, I can easily shift from 3rd to 6th once i am at or near highway speed. If I am in leisurely traffic I will shift 1-2-4-6. Once is a rare while I will shift 1-2-6 when on a road with a 50 mph speed limit. Why bother with the other gears when you can only poke around as fast as the looser in front of you. 5th gear is the least used gear in my car. I also will up-shift anytime I am behind a slow poke or even in a school zone. When I travel through the school zones in the morning I put it in 6th gear and get a hybrid like 50+ mph. Cool!

Technique #8 - Set a realistic goal to beat. This is really not a technique. After all you probably already have a goal. But setting a goal you have a realistic chance of beating can be more fun. A friend of mine calls this the mileage game. He plays the mileage game with every tank of gas. You always try to beat you best score from one tank to the next. Once we are getting close to our maximum mileage we need to set a goal we can reach. We are trying to make the most of all the tricks here. When I was doing my testing I initially set a goal of 31 mpg. However, I was at over 32 mpg by the end of the first day so I had to set a higher goal to keep pushing myself.

For the final mileage using all my techniques I hit 32.2 mpg. That is an improvement of 23.3% from our baseline. Is that significant enough of an improvement to get you to try it.

To get over 32 mpg in mix driving with a car that is EPA rated at 32 just on the highway took a lot of effort. I would pull out of my driveway shifting into second gear just as I hit the street. Then I pop it into neutral and coast all the way to the stop sign at the end of the street. It is downhill most of the way. I do the same when I get to that stop sign. I accelerate to about 35-40 mph and then shift into neutral. I can coast in neutral more than a 1/4 mile to the main road. And since there is a nice downhill section I actually get up to about 45 mph because of gravity.

Once you get the techniques down you need to get into the habit of resetting the average mileage readout on your car. I know people that do this each time they fill their tank. That works, but I prefer to do it every Monday morning. I try for the best mileage by Friday. I tend to ignore mileage on the weekends.

President Bush is trying to revive a promise his father made when he claimed he was going to push/help the automakers get 30% better mileage by 2010. We'll see if that happens. In the meantime if everyone followed my driving tips we could all get 23% better gas mileage. Right Now!

Imaging what that could do to the Oil Rights War... Uh... I mean the War on Terrorism. If we could reduce our need by almost 1/4 overnight. Wow!

People talk about boycotting the gas stations when prices get to high... why not just drive smarter now, so you are giving them less money. Easy! And it works no matter what gas sucking SUV you are driving. 23% improvement with nothing to buy, and nothing to lose. How can you beat that.

Follow the Leader

For one week I tried to see what it would be like to drive like the looser in the middle lane. I made sure to follow the car in front of me as much as possible. When I was in a two lane road I would usually drive in the passing lane. When in three or more lanes I staid in the middle lanes. I followed traffic without wondering what my mileage would be. After a week of driving like this I had an average mileage of 28.3 mpg. So the poor schlep in front of me on the highway causes me to get about the same mileage as just having and using the mileage readout on the dash.

Cruise Control

What about cruise control. Well, if you read the uphill/downhill technique you know that it flies in the face of cruise control. CC will use heavy engine breaking to slow you down as you go down hill, and it will accelerate rather briskly to maintain the same speed going uphill. Plus cruise control can't see down the highway at upcoming traffic congestion or that hill that is a half mile out. Regardless, I decided to try using cruise control for a week. This is difficult because you have to decide how to use it. The idea behind CC is to set it and forget it. But traffic will not allow that. What to do.

Well, I tried to do just that. I set the cruise at 73 mph, whenever possible. I attempted to hold it there as long as possible. If traffic was moving constantly at a different speed I would do my best to match it. Using cruise control for a week I managed to get 30.1 mpg. Not bad. Keep in mind that I did this the week after I managed 32 mpg. I still used all the other techniques when not using cruise control.

Conclusion

Well, I broke it down into 8 techniques and managed to increase my mileage from 26.1 to 32.2 mpg. That is an increase over 23%. That's real world mileage increases... by the driver not the vehicle. You can think of it this way... it makes driving more engaging. You have to be thinking about all these techniques, you have to constantly monitor you mileage, you have to scan traffic both in front and in back. There is a lot going on here. A friend of mine calls it "the mileage game." They put that little digital readout in the dash so you could play a video game while driving.

When I get great mileage I win the mileage game.

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