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Since gas mileage was recently brought up in the "Where do you normally fill up?" thread by rookie888, I thought it would be a good idea to have a discussion about gas saving strategies. His post contains a link to an article in the Toronto Star, which lists 10 gas-saving ideas from Jim Davidson's book, 75 Ways to Save Gas. The comments on this article seem to be quite negative, but I hope that the disucssions here can be a little more open-minded. In particular, I'd like to know what you think about nitrogen tires, synthetic oil, and various gas-saving driving techniques. I'm not interested in hearing about how I can use my vehicle less often - I'd just like to share and compare strategies for using less gas per kilometer.

There's no doubt that maintaining a good tire pressure improves fuel economy, and nitrogen makes this easier to do (especially when temperatures fluctuate). I personally use pure nitrogen in my tires, but it's more to avoid the hassle of checking tire pressure and to prolong the life of my tires. I just get the nitrogen levels checked & refilled when I take my car in for maintenance. I use synthetic oil for the same reasons: less engine wear means less repairs and longer lifespan. But it's great to know that these measures might also be slightly improving my gas mileage!

Probably the best driving technique is to avoid going too fast on highways. Most vehicles have an optimum gas mileage when travelling at a speed of 90 - 100 km/h, and gas usage at higher speeds increases quickly (at about 150km/h you're using twice as much gas per km!). I found a chart with mileage vs speed for 8 different vehicles. The rate that the mileage drops off (the slope) is pretty similar for the 8 different cars, so it stands to reason that most cars will suffer a similar rate of mileage loss.

On city streets, going too fast isn't usually a concern, though you should always think about going a little out of your way to use a highway instead of stop-and-go roads. Besides being stuck in a traffic jam, the biggest waste of gas on city streets is having to constantly stop and accelerate. Here are some of the techniques I use to minimize this penalty:
  1. Don't waste gas to get to that red light sooner! Preventing the guy in the next lane from cutting into your "shorter lineup" just isn't worth it. Release the gas pedal and coast up to the light. Another advantage to coasting is that the light might turn green before you get there, meaning you won't have to come to a stop at all (while that guy who raced ahead now has to accelerate from zero!)
  2. Time the lights. Look ahead to the next set of lights and try to determine if it will be green or red by the time you get there. Make use of the pedestrian walk lights (espcially the countdown type), as well as your gut feeling. On your regular commute you'll probably get to know how long each light is. If you think a green light will turn red, let go of the gas (resist the urge to try and beat it). If it's going to stay green, maintain speed or accelerate a little to ensure that you make it. If it is currently red but you think it will change soon, let go of the gas and change to the lane with the shortest line up, to make it less likely that you'll have to brake.
  3. Leave lots of space between you and the vehicle in front of you. Hopefully you do this anyway, for safety reasons. Drivers on city streets tend to vary their speed, and if you're tailgating them then you're likely applying the brakes every time they slow down a bit, and then re-accelerating to stay on their tail.
Next, there's aerodynamics. Having a roof rack attached can significantly reduce mileage, especially at higher speeds. Most of the air flows over the top of your vehicle, so interfering with it on the roof is going to cost you. Mythbusters showed that using A/C actually uses less fuel than it does to have your windows open, AT HIGHWAY SPEEDS ONLY (I think 80km/h was the break-even point). The Toronto Star article mentioned keeping your vehicle clean for smoother airflow - I'm not convinced that this is going to make a significant difference but I like to keep my car from getting too dirty anyway.

My last gas saving strategy is to avoid uneccessary weight in your vehicle. Don't go removing your spare tire or emergency blanket, but if you've got heavy cargo that you don't need, then unload it before you leave home. That includes a detachable hitch - if you're not going to use it for a while, take it off. A full tank of gas may be heavy, but a low tank is not only more likely to explode in an accident, it also increases condensation (thus diluting the gas and making is less efficient) and can damage your fuel pump which relies on the gas to cool it. I always fill up full, but I never try to go beyond the first click.


Million Dollar Journey also has an older (Jan '07) article about Saving Gas by Maximizing Mileage.
 

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My gas-saving strategy is to avoid driving ;)

This is a lot easier for me now that I live in a city; when I lived out in the country I had to use the car to get just about anywhere. But here I use public transportation and bicycle for 90-95% of my trips, and use the car only when I have to go out of town or if I have to haul something big or heavy. It typically takes me a month to go through a tank of gas.

I've timed it, and I can actually get downtown faster by bike or Metro than I can by driving, when you factor in the traffic and the minutes lost looking for parking.

We even decided to take our vacation this year by bike, leaving from our front door and taking bike paths and small roads to the border and going around part of Lake Champlain, coming back up through the islands before heading home. Our only "fuel" costs will be our food and water.
 

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Out of curiosity, a while back I started tracking my mileage, writing down on my receipts my odometer at fill up and tracking it in my spreadsheet. I can notice the difference when I do more highway driving. Recently, due to the age of the car (and the driver :D), I've started driving slower, not accelerating too fast or going over 120 too often. Again, I've noticed the increase in mileage.

I was surprised about not filling up the gas tank in the Star article too. I've always heard you shouldn't let it drop below a quarter tank due to the build up of something (can't remember). Never thought of the weight issue before.

Also, I don't think it was mentioned, but unless your engine specifically requires it, do not fill up with premium gas. Regular is all you need, and will save you 10-12 cents per litre.
 

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how does the nitrogen inthe tires tihng work? Never heard of it, but I'm fascinated!!!
I believe it slows down the rate at which your tires deflate over time, probably since pure nitrogen doesn't escape as rapidly from the tires as regular air (which is mostly nitrogen anyway, but contains about 20% oxygen as well as a variety of trace gases).
 

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Discussion Starter #7
how does the nitrogen inthe tires tihng work? Never heard of it, but I'm fascinated!!!
When you fill your tires with dry air, you're putting in about 78% nitrogen, 21% oxygen, and 1% other gases. But water vapor can account for up to 5% of the air under the worst conditions. The density of water vapor fluctuates more than dry air, so removing humidity can help keep your tire pressure more consistent. Supposedly the water vapor can increase wheel rust, but I haven't heard of this being a common problem. Using pure nitrogen avoids any problems caused by water vapor.

Another benefit for pure nitrogen is that you eliminate the smaller oxygen molecules, which more easily diffuse through the porous tire walls. So nitrogen tires will maintain their optimal pressure longer, leading to better mileage and more evenly distributed tire wear. That's the theory anyway; I haven't seen any scientific studies that show that pure nitrogen makes a noticeable difference.

Nitrogen at normal temperatures is inert, so it won't attack the rubber in your tires like oxygen does. Oxygen attack has been researched and proven, though its effects are mainly only seen in older tires.

There's also a safety benefit, since nitrogen doesn't support combustion like oxygen. Aircraft tires are normally filled with pure nitrogen, but on March 31, 1986, Mexicana Airlines flight 940 had a tire improperly filled with air instead of nitrogen. An overheated landing-gear brake caused the tire to get hot and explode, rupturing fuel and hydraulic lines. 167 people died in the crash. Of course, the chances of your tires getting hot enough to catch fire is very slim, but at least you can be assured they won't explode!

One final side benefit - you get cool green valve caps and the bragging rights that go with them!

By the way, if you get your new tires at Costco (be prepared for a long wait), they will fill them with nitrogen.
 

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I find on long trips that putting the car in neutral when going downhill makes a difference. I once got over 100 km more out of a tank of gas simply by using this strategy during a trip from Toronto to Sudbury and back. There is a long stretch up highway 400 that is very hilly so every time I got to the top of a hill, I would put the car in neutral and coast down the hill - sometimes for up to 2 km at a time. Made a huge difference.

Do a google search on "hypermiling" to get other strategies for getting a lot more mileage out of a tank of gas.
 

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I find on long trips that putting the car in neutral when going downhill makes a difference. I once got over 100 km more out of a tank of gas simply by using this strategy during a trip from Toronto to Sudbury and back. There is a long stretch up highway 400 that is very hilly so every time I got to the top of a hill, I would put the car in neutral and coast down the hill - sometimes for up to 2 km at a time. Made a huge difference.

Do a google search on "hypermiling" to get other strategies for getting a lot more mileage out of a tank of gas.
This is fine for a manual transmission car as the driver is used to quickly engaging the clutch and matching the engine's RPM to avoid stalling, but for an automatic and an inexperienced driver, could be dangerous.

Essentially you are out of control of your car since if acceleration was needed in an emergency, there would be a significant delay.

Mythbusters looked at A/C versus windows, and as well slipstreaming behind a big rig. For the second, you could be a good ways back and still be taking advantage of the reduced drag.
 

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Park far away from stores in parking lots - mileage is very poor in parking lots. An added benefit is a bit more exercise from walking.

If possible, pull through the stall so you are face-out parking. Putting car in reverse and backing out uses a surprising amount of gas.

Ensure your tires are properly inflated.

Keep your car maintenance up to date - most people do oil/air filter, but also consider things like fuel filters, oxygen sensors, spark plugs, etc.

Use synthetic motor oil - especially low weight type.

If doing multiple errands, drive out to the furthest one first - it will allow the engine to warm up fully.

Try to do multiple errands at one stop.

Don't use drive-thrus. Park and go into the store.

If at a prolonged stop (i.e. slow train crossing tracks in front of you), turn off your car.

Whenever possible, don't use A/C - Fan on and window open are both better (except keep window closed at highway speeds).

Don't idle you car for long when you start it up - once it revs down, start driving gently. The car runs very inefficiently when idled from cold.

Using these strategies I average about 7.9 L/100kms in a 1998 V6 Toyota Camry which is quite a bit better than the new EPA estimates in about a 60/40 mix of city/hwy.

There are more extreme measures that I don't employ that you can read about at hypermiling webistes. I tried out a few of them but felt unsafe.
 

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Discussion Starter #12
Mythbusters looked at A/C versus windows, and as well slipstreaming behind a big rig. For the second, you could be a good ways back and still be taking advantage of the reduced drag.
I've heard of slipstreaming aka "drafting" as a common strategy in car racing and cycling, but I never considered it to be significant enough to try tailing a large vehicle on the highways (safety concerns aside). But I found the results of the Mythbusters episode, and it turns out you can improve your mileage by up to 39% if you're insane enough to tail 10ft behind a big rig. True, you can stop faster than the big rig, but at highway speeds that 10ft gap could close faster than you can hit the brakes. Other dangers include rocks being flung at you by the big rig's tires, inability to see what's ahead (debris on the road might pass under the big rig but not under you), driver of the rig might not be able to see you, and there's even a chance of being killed by an exploding tire. In the same episode of Mythbusters, they confirmed that an underinflated big rig tire could disintegrate violently and that the flying debris has enough velocity to decapitate a dummy right through the windshield. Of course the chances of this are probably far less than say, an animal jumping out in front of your vehicle and decapitating you. Dangers aside, another reason NOT to tailgate is that it can really irritate the big rig driver.

Another thing to consider is that many big rigs I've encountered often travel in excess of 100km/h and by following at the same speed, you aren't getting your optimal gas mileage. Depending on the speed and how close you tail the rig, it may actually cost you more gas to keep up.

Personally, I think 100ft is reasonably safe for me to follow a big rig. The driver can likely see me at that distance, and probably wouldn't be very annoyed since you aren't exactly tailgating. If that gets me 11% better mileage, then it's probably worth trying. RV's, moving vans and other large vehicles would probably also work pretty good, maybe even better since they are lower to the ground and would thus provide a better wind-shield for a car.
 

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I thought people would have mentioned this by now: Siphon gas from other people’s cars. :)

Carpooling also saves on gas...if you can go in one car instead of two or three, the average gas mileage per person is fantastic.

Also, wait until you have several errands to do at once instead of popping to one store to just pick up some milk.
 

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Slipstreaming behing a big rig is dangerous. How often do you see pieces of tread from a rig on the side of the highway? A lot more often than you see dead animals or other debris. Where do you think those pieces came from? As someone else pointed out, it can do a lot of damage.

Nitrogen in tires is just the latest consumer fad. Air is 80% nitrogen already. This idea started in racing so the pit crew could accurately predict tire pressure variation as the tire heated up under racing loads. And as far as fire protection, forget it. There is a lot more air outside the tire than in it, and all that air has 20% oxygen that will support combustion.

Want to save gas? Keep tires properly inflated, get a tune up (include changing your air filter), and don't accelerate too fast.
 

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Another thing to consider is that many big rigs I've encountered often travel in excess of 100km/h and by following at the same speed, you aren't getting your optimal gas mileage. Depending on the speed and how close you tail the rig, it may actually cost you more gas to keep up.

Personally, I think 100ft is reasonably safe for me to follow a big rig. The driver can likely see me at that distance, and probably wouldn't be very annoyed since you aren't exactly tailgating. If that gets me 11% better mileage, then it's probably worth trying.

I've found following big rigs usually helps because you can often find one going 100-105 km/h and use it to help keep a pace (and with a truck in front of you, the speed demons seem to understand that you're only going the limit). Many of the trucks are themselves speed demons, but not all : )

I've found you can still get about 2-3% of benefit even a safe distance behind a truck -- 100 m rather than 100'.

Also for me, "properly inflated tires" means keeping my tires slightly hard at 40 PSI. The tips often say to keep your tires “properly inflated”, but the ideal pressure is usually some compromise between the figure given by your car manufacturer on the door jamb — in my car's case, 32 PSI, which is a compromise value between ride comfort and fuel economy, and what should be considered the minimum — and the max sidewall rating of the tire, 51 PSI for mine.
 

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My Technique

I do a few things.

1. Carpool whenever possible. I drive every second day.
2. Keep the RPM's under 3000 whenever possible. This means gradual starts but it isn't as bad as you think.
3. Neutral. I have a larger hill on my way to work. I put it in Neutral and 4km later I put it back in gear. Unfortunately I'm pretty sure that my driving up the same hill on the way home nullifies the savings.
4. Keep a long eye-lead. It's safer and I time the lights as much as possible (sometimes throwing it in Neutral for this as well).
5. You get Zero Miles Per Gallon while idling. I will turn of the car when it is feasible.
6. Drive light and clean. I don't store stuff in my car and a clean car has less air resistance.

I fill to the brim simply because I hate doing it. I want more miles per tank than anything else. I haven't tested it like they did in the 50L Challenge, but I did learn that there is still 100km+ in my tank after the light comes on. For me, that is my new signal that I have to fill up within the next 40km.

50L Challenge

I'm also reconsidering my winter tires. I have noticed a hit at the pumps once I put them on. Since I need to buy some new ones, I might go thinner so I don't have to fight through the snow as much.
 

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I do a few things.

1. Carpool whenever possible. I drive every second day.
2. Keep the RPM's under 3000 whenever possible. This means gradual starts but it isn't as bad as you think.
3. Neutral. I have a larger hill on my way to work. I put it in Neutral and 4km later I put it back in gear. Unfortunately I'm pretty sure that my driving up the same hill on the way home nullifies the savings.
4. Keep a long eye-lead. It's safer and I time the lights as much as possible (sometimes throwing it in Neutral for this as well).
5. You get Zero Miles Per Gallon while idling. I will turn of the car when it is feasible.
6. Drive light and clean. I don't store stuff in my car and a clean car has less air resistance.

I fill to the brim simply because I hate doing it. I want more miles per tank than anything else. I haven't tested it like they did in the 50L Challenge, but I did learn that there is still 100km+ in my tank after the light comes on. For me, that is my new signal that I have to fill up within the next 40km.

50L Challenge

I'm also reconsidering my winter tires. I have noticed a hit at the pumps once I put them on. Since I need to buy some new ones, I might go thinner so I don't have to fight through the snow as much.
Mostly good advice but I think you probably mean to keep revs under 2000 rpms when possible - it is actually very easy to keep them under 3K. You will notice much better mileage at 2K.

I would suggest most people be careful with putting the car in neutral - don't use it in traffic until it is almost like second nature to you as you don't want to be caught in a situation when you need to suddenly speed up but have forgotten the car is in neutral. I do use this myself but it is second nature to me now. The other thing is that some automatics cannot be put in neutral while moving for extended periods of time - has to do with lubrication of the transmission. This type of driving is referred to as NICE-on coasting (stands for neutral internal combustion on).
 
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