How to get good gas mileage.

[Reijo Silvennoinen]

Since Mako so kindly brought up the issue of how to improve your gas mileage, it got me to thinking that this might be useful information for all of us.

Maybe all of you have heard of the hyper-mileage people. People who go to extreme extents to get the maximum gas mileage out of their cars. For instance I saw a news (CNN I think) article and other news references to them recently and how they often get twice the rating of their car's gas mileage - e.g. a 24 mpg Accord getting 50 mpg etc.

So I thought maybe there is something to be learned there.

Here's a few ideas off the top of my head (perhaps more from a motorsports perspective) and some tricks I use and others I have merely heard of:

1. One of the most interesting: A few years ago I came across an article of someone having done some research and discovering that accelerating slowly to freeway/highway speeds was NOT the most efficient way to obtain optimal gas mileage. They found that moderately (whatever that means - probably no VTEC for me!) brisk acceleration to get to "cruising" speed and the higher gears actually yielded better mileage in the long run because you ended up spending more time in higher gears.

2. The obvious one - slow down a bit. 80 mph does not get as good gas mileage as 45-50 mph. However, notably my '88 Turbo Daytona actually got better mileage at 80 mph than at 60-70 mph ... a function of really high gearing....lugging up hills when not in the power band! Weird, but true. So in that car, I drove faster in order to get better gas mileage. ;)

3. My '90 MIata actually got slightly better gas mileage on mid-grade fuel than regular or premium. Also felt more peppy on mid-grade according to my butt-dyno. I documented the evidence over many years of ownership on excel spreadsheets. Why, dunno. Wouldn't do it again.

4. Keeping speed up in corners. Drive a good line around those freeway ramps and you will not have to slow down nor speed up as much. Besides, it's good practice.

5. Drafting - yep some of the hyper mileage guys tuck in behind semis and tag along for the ride. I'm not sure I recommend following others too closely - besides you might get a ticket. What I do is less dangerous: Do the bulk of the accceleration when in the "draft" of a vehicle - e.g. behind it and off to the side of it (like riding the wake of a boat). Maybe I should get into NASCAR?

6. Hypermilers: (I like this idea) Park such that you can pull straight out instead of having to back up etc. Also manuevering the vehicle is better done when the engine is warm and more effecient.

7. Shutting the engine off at long lights. If you KNOW the light is a long one (like the one outside my place), you might shut the engine down while you are waiting. This is something I heard on TV many years ago - good idea but I still wonder about the extra wear on the starter etc.

8. Back many years ago while a teenager I was visiting my uncle in Finland and he used an interesting tactic to save fuel (yes, fuel was about 2.5-3 times more expensive over there even then!). In particular I remember the wild drive to his summer camp on the lake in his Ford Taunus (European model) wagon with the whole family on-board. The road was curvy, hilly (often with curves on the hill) and gravel. Think of the WRC Finnish rally - Rally of the 100,000 lakes - that is where I was born. Well, we would do 4-wheel drifts around the corners and if there was on-coming traffic, he would simply change the drift angle to fly by the other car! Scared the beejesus out of me! And did I mention he drove pedal-to-the-metal continuously? There was no speed limit there at that time. Obviously he didn't mind. Ever wonder why so many rally drivers come from Finland? Now you know the rest of the story!

But, I digress!

For better fuel economy, he used to put the std. transmission into neutral and glide down hills, letting the engine idle. Once at the bottom it promptly went to the floor boards again and off we went!

Your turn!

Reijo

[Ashley Armstrong]

My dad, who is much smarter than I, tells me that wind resistance goes up drastically above a certain speed threshold--maybe 60 mph? Something like that.

[Curt Luther]

2. The obvious one - slow down a bit.

I've gone from getting 30mpg to 33-34mpg by doing this. I used to set the cruise at 77 in 65s and 83 in 70s. Now it's 70 and 75. It's also helped that traffic seems a bit lighter lately thanks to higher gas prices and the 210 now going all the way through from SB to Redlands. More time in "cruise" and less stop and go.

[Reijo Silvennoinen]

Just checked my gas mileage on the S2000 - got 25.116 mph on the last tank (incl. trip to San Diego - drive along the Beach Cities - so some stop-and-go there plus a bit of driving around the city).

Mileage has gone up a couple of points and I'm going to attribute it to: new spark plugs and set the solid-lifter tappets/valves. Engine is obviously running more smoothly and putting out more power - again by my butt-dyno.

So, a tuned vehicle is a good thing - including an air filter that is clean/good condition.

Note that I also run synthetic fluids everywhere (engine, transmission, differential) which offer less resistance - hence better fuel mileage ... and more power to the ground!

Reijo

[Mako Koiwai]

A german study a few years ago said that the most fuel efficient method of driving was fairly brisk, 3/4 acceleration to speed, then coasting back down again. Not very practical. If you've ever had a car with an instant mileage gauge, you KNOW that acceleration is the big gulper of fuel, and that coasting does give the best MPG. So ... get off the gas early when you know that light up ahead is red or definitely going to change.

Keeping ones tire pressures up is always good. Using narrower tires also helps.

Thinner oil ... one of the reasons the manufacturers have gone to 5/30.

AC over open windows is a wash ... more work for the engine vs aerodynamics.

If you've even pushed an AWD car like a Suby, you know there is a LOT of mechanical friction in the driveline.

I get better mileage with 91 in my Toyota Previa ... the engine can take advantage of the higher octane, but not enough improvement to off-set the hight price of Super.

A colleague recently sold his SUV and bought a Prius. Saves $300 in gas a month (long commute from Oxnard) ... so his $500/month car payments are nicely off-set.

[Mako Koiwai]

Note that synthetics in the tranny can mean harder downshifts, since the synchros need some friction. In fact you can buy friction plus tranny fluids to make easier shifting, ie. GM Synchromesh, Redline MT-90. You can run a percentage of those fluids in your gearbox.

[Will Kalman]

Drafting is awesome. Today, I got 46.x mpg driving 31 miles from Porter Ranch to Pasadena. My best is 47.0. The car is rated at 38mpg highway. Mileage back home is a little worse but I can almost always top 40mpg for the 62-mile round trip. Climbing the hill to my neighborhood steals 1.5mpg from me and I don't make it back up the next morning on the way down because I have to use the brakes and the engine is running rich and/or high idle when cold.

Here are a couple things I've learned thanks to the Scangauge device that I've plugged into my OBD2 port:

1) Coasting in neutral vs. just lifting off the gas: Common knowledge is that cars turn off the injectors when you let off the gas. This doesn't appear to be true in my '06 Civic as the device indicates 0.2GPH burn rate when off-throttle at highway speeds which I think is due to emissions - keeping the catalyst lit rather than running "cool" unburned fresh air through it. That's the same burn rate as idling but it's not a wash as engine drag is stealing energy out of the system. Plus, in neutral you can keep an acceptable speed on a lesser grade or coast to a higher speed on a given grade or coast out further before having to apply power again.

2) Traffic anticipation. The brake is evil. You burn gas to put energy (momentum) into your car, then turn it into brake dust, then have to burn more gas to get the energy back into your car. Terrible. There are three main places on my daily commute where traffic tends to slow. I always look waaaay ahead for brake lights. If I see them, I shift to Neutral, let a gap open up, and enjoy the benefits of the gas I've already burned. When this works perfectly, you coast up to the car in front just as it starts to accelerate after the slowdown.

3) Drafting. You don't have to hug the bumper of that SUV, U-Haul, or big rig but choosing to follow large vehicles vs. not following them adds up. Most of the big vehicles are also slow but Mr. Compensator in the 400hp Escalade who has to show the world how bad-ass he is at 70mph is your friend! I got 43mpg driving hom from Vegas by following the toy haulers towed by motorhomes - big vehicles with low floors practically pull you along!

4) Smooth out the flow. In stop-and-go (or slow-and-go) traffic, leave a big gap open to absorb the "rubber-banding" effect and keep a steady speed. If you could drive at a steady 40mpg, you'd get extremely good mileage. Going 10-70-30-60-20 destroys mileage (and wears out your car in numerous ways).

This is an interesting experiment:
http://backreaction.blogspot.com/2008/0 ... -jams.html" onclick="window.open(this.href);return false;

This guy has thought about it a lot and has some very good observations:
http://www.eskimo.com/~billb/amateur/tr ... ffic1.html" onclick="window.open(this.href);return false;

Driving like this is a fun, legal, productive, and challenging game to make the drive go by.

5) Don't carry stuff on the outside of your car is you can avoid it. Roof-top carriers in particular are a double-whammy - not only to they increase the frontal area, they ruin the Cd of your car (the relationship of frontal area and drag). Putting my mountain bike on the hitch-rack of my Civic loses me 4-5mpg! Unfortunately, a 5-inch-travel mountain bike doesn't fit easily in the trunk and the odds of scratching the car with numerous packing/unpacking cycles are pretty good so I take the hit. I'd try harder to pack the bike if I had to go on a long trip.

6) Don't let your engine warm up for a long time before driving. Idle consumption in my Civic when warm- 0.2GPH. Idle consumption when cold - 0.8GPH. Use the 0.8GPH to drive - which also makes the warm-up time much shorter. Start it up, idle for 10-15 seconds to make sure all the lubricants are circulating, then drive mellow until the temp rises.

7) NUMBER ONE - the gas you don't burn costs $0.00/gallon! Combine multiple trips into one, take a bicycle, etc.

[Will Kalman]

My dad, who is much smarter than I, tells me that wind resistance goes up drastically above a certain speed threshold--maybe 60 mph? Something like that.

It may *feel* like there's a critical speed, but here's the real deal:

Aero Drag = (speed difference)^2
HP to overcome it = (speed difference)^3

Doubling the speed generates 4 times the aerodynamic drag which requires 8 times the horsepower to overcome it. Period. Rolling resistance is fairly linear - double the speed is double the drag.

So 10% higher speed (say 66mph vs 60mph) = 21% more drag = 33.1% more power required. You gain a little of that back becuase car engines are more efficient at higher % loads. That's why a small 100hp engine gets better mileage than a large 400hp engine- even in the same car at the same weight. The small engine may be working more effciently at 25% of full output than the large one at 10%. (Not real numbers)

Now, if your car is stuck at an inefficient RPM (like Rejio's example), a different speed may yield better mileage.

[Earl Merz]

5. Drafting - yep some of the hyper mileage guys tuck in behind semis and tag along for the ride. I'm not sure I recommend following others too closely - besides you might get a ticket. What I do is less dangerous: Do the bulk of the accceleration when in the "draft" of a vehicle - e.g. behind it and off to the side of it (like riding the wake of a boat). Maybe I should get into NASCAR?

You will be suprised if you do that to me. Following to closely or right beside... big no-no. There is a reason for the No-Zone.

What happens to your vehicle if I would have a blowout? You really want a 150lb tire flying at your car? 150lb traveling at 55mph? Think of the damage... Or if you are lucky enough to get caught by a super single... 200lbs at 55mph. It's aslo hard to see you when you are sitting back there, what happens if the driver has to make a sudden move?

I have had people try to draft me, they are not usually to friendly when they pass me after I decreased my speed to under 35mph on the freeway. People that ride beside me usually get an eye full of tires running on or slightly over the lane markers. Or a bit of trailer swinging. I'm not an asshole when I drive, as long as you leave me my space. Invade my space and all bets ore off

[Marshall Grice]

Apparently keeping a turbo'd car out of boost is good for 50% better gas mileage. Took a trip up to my parents house this weekend. Utilizing driving techniques that keep the ecu in closed loop mode (ie not the 10:1 AFR open loop mode) yeilded an average of 31.5mpg in my Evo. I normally get 20mpg average. Hell it's only rated for 25mpg freeway. It's REALLY hard to take on/off ramps with out getting on the gas though.

[Earl Merz]

My old truck, Cummins ISM powered, would routenely get me 10.2-10.5mpg round trip to SD and back. ULSD dropped that to 9.8-10.2mpg. But the new truck with the newer emissions crap gets 8.5-9.0 on the same trip. Yea Detroit

[Michael Palero]

Since Mako so kindly brought up the issue of how to improve your gas mileage, it got me to thinking that this might be useful information for all of us.

Maybe all of you have heard of the hyper-mileage people. People who go to extreme extents to get the maximum gas mileage out of their cars.

So I thought maybe there is something to be learned there.

Here's a few ideas off the top of my head (perhaps more from a motorsports perspective) and some tricks I use... to save fuel ... we would do 4-wheel drifts around the corners and if there was on-coming traffic, ... simply change the drift angle to fly by the other car... For better fuel economy, ...

...

Reijo

Did you hear that everyone? Reijo says Drifting saves gas!
No wonder Patty always gets more MPG than me!

[David Avard]

Well, I started typing this and then lost control of the laptop, so, now it's two hours later.

With old bricks, or pickups and RVs, 45mph is about where the aero drag becomes more of a factor than friction drag. Modern, aerodynamic cars might be able to go a little faster, but not too much.

But, gearing and torque converter lockup (for autos) can also play a part. For my Jeep Grand Cherokee, it doesn't lock up the torque converter in OD until it gets to 48 mph (it locks up drive at 32 mph), so 50 mph is more efficient than 45 mph, and towing in OD is actually a little better mpg at 72 mph than at 65 mph in rolling terrain (due to not unlocking the TC at every incline). That said, the difference between 55 mph (road rally on back roads) cruising and 70-75 mph is about 20% (22 mpg vs 17-18 mpg). And that is with an AWD SUV.

Driving around Yellowstone (mostly at 40-45 mph, but with 120 miles at 55-60 mph leaving the park) in our Protege we got 38 mpg for the tank, and I'd never seen over 30-32 mpg on normal highway driving.

And Earl, having a vehicle behind your trailer actually improves your gas mileage by filling in that big space behind the trailer. And they don't have to be 10-feet back. 100-120 feet will do.

Having had a tire blow on a trailer in front of me at 60 mph (karma for the truck driver), it's a little surprising. I was driving a (my) Uhaul at the time, so no damage to my vehicle, but I'd have hated to hit that thing in the Honda. Of course in the Honda, I could have swerved to avoid it, and not left the lane.

[Will Kalman]

What happens to your vehicle if I would have a blowout? You really want a 150lb tire flying at your car? 150lb traveling at 55mph? Think of the damage... Or if you are lucky enough to get caught by a super single... 200lbs at 55mph. It's aslo hard to see you when you are sitting back there, what happens if the driver has to make a sudden move?

Good points. But just to get the physics right, your blown out tire isn't going to get to 0mph in the distance between your truck and a following vehicle. In fact, the closer they are the lower the potential contact speed! Large chunks of tire are another issue, but they're not a 150lb tire.

And I never "draft", I just choose to follow rather than not follow at a reasonable distance. And I'm "on guard" when I do so, knowing that I dont' have as much time to react.

You don't need to see the car behind you if you make a sudden move. Make your move and let the following driver fend for themselves in the situation they've set themselves up for.

And on a truck/trucker related note, this whole idea of "<--- Passing Side | Suicide --->" bugs me. If there are four lanes of freeway and the trucks are in the #3 lane, why should half the freeway be limited to truck speeds. I'm talking about the CITY. On the highway, it's another matter and the rule should be followed more strictly.

And I'm the guy who always slows and signals the trucks to move over in front of me. Not for drafting reasons but becuase even driving a 24' Uhaul, I know what a bitch it can be to get over in traffic. The "thanks" taillight flash is always appreciated, too.

[Will Kalman]

Well, I started typing this and then lost control of the laptop...

Drafting the desktop machine too closely, were you?

[Rick Brown]

For better fuel economy, he used to put the std. transmission into neutral and glide down hills, letting the engine idle. Once at the bottom it promptly went to the floor boards again and off we went!

Your turn!

Reijo

If I'm stuck behind slower traffic going down the hill to Lake Elsinore on Ortega Hwy east, on either the bike or in the SUV I often do just that. The bike I put in neutral and shut off the engine, but leave the ignition on, and the SUV I just put in neutral. I most cases I'm still on the brakes since I coast faster than some of the slow pokes are willing to drive. Not sure how cost effective it is since I'm now using the brakes when I normally wouldn't. If I put the SUV in "2" I don't need to brake much at all, engine braking is enough to control speed.

[Marshall Grice]

5. Drafting - yep some of the hyper mileage guys tuck in behind semis and tag along for the ride. I'm not sure I recommend following others too closely - besides you might get a ticket. What I do is less dangerous: Do the bulk of the accceleration when in the "draft" of a vehicle - e.g. behind it and off to the side of it (like riding the wake of a boat). Maybe I should get into NASCAR?

You will be suprised if you do that to me. Following to closely or right beside... big no-no. There is a reason for the No-Zone.

What happens to your vehicle if I would have a blowout? You really want a 150lb tire flying at your car? 150lb traveling at 55mph? Think of the damage... Or if you are lucky enough to get caught by a super single... 200lbs at 55mph. It's aslo hard to see you when you are sitting back there, what happens if the driver has to make a sudden move?

I have had people try to draft me, they are not usually to friendly when they pass me after I decreased my speed to under 35mph on the freeway. People that ride beside me usually get an eye full of tires running on or slightly over the lane markers. Or a bit of trailer swinging. I'm not an asshole when I drive, as long as you leave me my space. Invade my space and all bets ore off

i've been hit by several tire treads that have been kicked up by traffic in front of me. turns out they don't do any damage other then a bit of a skid mark and maybe some small scratches. I think your over estimating the weight of the tire tread. Its not like you drop a complete tire out the back when it blows. although If I were on a motorcycle it would suck a lot. I hit a newspaper once and it almost pulled my arm off the hand grip and i almost crashed trying to get the damn thing off of me.

[Jayson Woodruff]

Good points. But just to get the physics right, your blown out tire isn't going to get to 0mph in the distance between your truck and a following vehicle. In fact, the closer they are the lower the potential contact speed! Large chunks of tire are another issue, but they're not a 150lb tire.

Not exactly. This isn't a piece that falls off the car and obays a normal conservation of momentum. It gets FLUG from the wheel. Which relitive to the trucks speed can be 50-60mph towards you (0mph relitive to the ground).

I know Earls points. But I do it anyways too. I'm pretty senesitve to not pissing people off, and only tuck in behind, not to the sides. I know I can stop faster, so its really just a matter of reaction speed and paying attention. It's easy to tell when a trucker doesn't want you there, so you just go around to the next one that doesn't care. This does induce a lot more debris chips n the hood/windshield though.

Oh yeah, the low floor rigs are the best. Caught a ride behind one for about 1/3 the way to Atwater a few years back. I couldn't hold the pedal high enough, had to blip it.

BTW, on the injector shut off thing... What RPMs are you trying to cost in gear at? I had a A/F meter on the Geo and anything above about 1800 it would shut off the fuel, but then try to 'idle' below that. So I down shifted to keep the fuel off until it'd turn back on in second gear, then coast out of gear. This was an OBDI car though. Might be different now. The prius will kick on the ICE if I've used only battery for a while, even if it's still well charged. So I assume its trying to warm things up again.

Jay W


Jay W

[Reijo Silvennoinen]

Earl, what it appears to me is that you think that I sit around drafting a truck (like the hypermilers). I agree with you that drafting/tucked in tightly behind ANY vehicle is not a good idea.

Close drafting is not what I practice nor advocate...nor was it what I was talking about.

In fact, quite frankly, I just don't drive that slow (as any of my passengers will attest) despite the price of gas. I hate being among the slow-moving, non-attentive ... ok, I will be politcally incorrect - the imbiciles! I find it scarey/dangerous to drive among them and will not do it! }:)

Therfore, in order to clarify what I'm advocating is ACCELERATING while in the draft of another vehicle.....and backing off on the gas as you go by the vehicle and back into the wind ... e.g. timing of your acceleration while passing. That way you spend less time accelerating (in order to pass slower moving vehicles).

And, like the others mentioned, if you choose to do some drafting, you do not need to be immediately behind the vehicle in front of you to get some benefit.....keep a safe distance. On a motorcycle/convertible you can feel the difference more easily...

[Will Kalman]

Not exactly. This isn't a piece that falls off the car and obays a normal conservation of momentum. It gets FLUG from the wheel. Which relitive to the trucks speed can be 50-60mph towards you (0mph relitive to the ground).

BTW, on the injector shut off thing... What RPMs are you trying to cost in gear at? I had a A/F meter on the Geo and anything above about 1800 it would shut off the fuel, but then try to 'idle' below that. So I down shifted to keep the fuel off until it'd turn back on in second gear, then coast out of gear. This was an OBDI car though. Might be different now. The prius will kick on the ICE if I've used only battery for a while, even if it's still well charged. So I assume its trying to warm things up again.

That's why I differentiated between a 150lb tire and a portion of tire which is more likely to come "back" at you at speed.

I know the Escort ('91) would shut off the injectors until RPM dropped below about 2000RPM - I could hear it plainly in the loud exhaust. Lift-throttle above 2000RPM would give a sound like shutting off the key, a steady drone. Below 2000RPM there was notable combustion sounds/burbling.

I think it's changed in recent years and I think it's because of emissions as the catalyst could cool off too much with out hot exhaust gas keeping it lit. The only evidence I have of injectors not shutting off on my Civic is that my Scangauge device says 0.2-0.3GPH while my foot is off the gas. It seems to go to 0.3 at higher rpms so I think there is some fuel regulation going on. 0.2GPH is always the rate at idle and I know that the precision of that displayed number is low (although I believe the internal accuracy to be high).

I choose to use Neutral downhill because the engine drag takes some of my hard-earned energy away (see point 1 in my previous email). And if the gas consumption is the same in Neutral vs. in gear, there's no point in staying in gear. I'm just lifting at highway speeds in gear - 2000-3500 RPM.

[Will Kalman]

Not sure how cost effective it is since I'm now using the brakes when I normally wouldn't. If I put the SUV in "2" I don't need to brake much at all, engine braking is enough to control speed.

There's no difference in cost effectiveness, you're "bleeding" the energy in either case - either through the brakes or engine drag. And speaking of that, I'd rather wear out my brake pads than my engine/transmission. And almost every car made to day has way better brakes than in years past when people were instructed to downshift on long hills (think 4-wheel drums).

But there is always the specter of showing a cop that you're coasting downhill with continuous use of the brakes. Coasting (Neutral) is illegal. So is speeding and none of us do that, right? }:)

[Bob Beamesderfer]

But there is always the specter of showing a cop that you're coasting downhill with continuous use of the brakes. Coasting (Neutral) is illegal. So is speeding and none of us do that, right? }:)

When I was commuting on the 241, people were always tapping the brakes going down the hill from the toll plaza, which going north is three miles. I don't think cops would know a coaster from anyone else.

[Sebastian Rios]

The Titan gets horrible mileage mainly because I only use it to go 3.9 miles to work and to tow the car.

It has one of those instant MPG gauges but it goes all the way to 60 which is kind of a joke, it only goes that high coasting downhill. I've been taking it out of gear and coasting to the next stop as often as possible, but I haven't been able to see a difference.

[Mako Koiwai]

Just tanked up. Really disappointed! This week I really dawdled along to work ... keeping it around 65 on the fwy, following trucks, coasting, often and early, easy acceleration. 19.4 mpg with my egg shaped Previa. Highest bill ever ... $77+ at ARCO ... but that's with 89 octane. Going to try the middle grade ... as Reijo sort of suggested.

[Ethan West]

I got 12.9 MPG on my last tank. I guess thats what happens when all of my trips are short trips around town.