How To Save Gas ?

[gregb]

Many people make the mistake of thinking only the gear of your transmission matters in your fuel consumption, and that the higher the gear, the better off you are. This not true. Most cars actually have a dual peak in fuel economy, and the top gear may not be the best choice if your engine has to operate in the low 1000's in order to use it. The engine efficiency varies over the RPM range, and most engines generate their best brake specific fuel consumption at around 2700 - 3000 RPM. This means, that you get the most power per drop of fuel when your engine is running in this range.

Now, competing with this are inefficiencies from your transmission as it spins faster, as well as wind resistance from your car moving faster. If you had a 100% efficient continuously varying transmission, then your optimum profile would be to accelerate at about 3000 RPM until you reach your final speed, and then reduce the throttle to maintain that speed.

Even this isn't necessarily correct. A better method (but annoying as hell) is to actually drive at 3000 RPM until you hit the speed you want, then coast until your speed has bled off to the point Somchai's grandma is passing you, then accelerate again at 3000 RPM, rinse and repeat. The reason this works is because it allows you to operate your engine at absolutely the most efficient setting during every moment of your trip (the fuel used during idle has the effect of causing the best speed to reengage the engine to be higher than 0).

In practice, inefficiencies of various other components enter into the equation, which is why you see the effect above where accelerating improves fuel economy up to about 2000 RPM. It is important to know at what RPM your engine reaches its peak brake specific fuel consumption if you want the best fuel economy. You should target your acceleration about 200 RPM below this number.

The tradeoff between brake specific fuel consumption and wind resistance is also why cars have an optimal speed for travel (ignoring the pulse method above.) It is NOT true that 90 kph is always better than 100 kph. This number is very, very dependent on the Cd of your car. A very low Cd will cause the wind resistance curve to intersect the increasing efficiency of higher engine RPMs at a higher speed. My Altis 1.8 gets its optimum fuel economy at about 99 on the highway, at around 2200 RPM. Beyond this speed, the effect of wind resistance is greater than the increased fuel efficiency of the engine.

I bristle when I hear people say "90 is better than 100", because that is very dependent on your car. It may have been true 30 years ago when cars were shaped like boxes. It ain't true today. Every car has a different optimum speed based on its Cd and engine type, and in many modern cars that point is above 90, but I think it rarely goes above 105.

To the OP, if you want to find your optimum speed, you will need to make a very careful study over flat terrain for several hundred kms. driving carefully at many different speeds. Fill your tank, drive 200 km at one speed. Fill your tank again. Record the fuel used. Do this several times at the same speed and average the results to remove the effects of wind and small differences in how full you got your tank. Over a period of several months you can build a very accurate picture of how your vehicle performs.

Tire pressure is also extremely important in fuel economy. The higher the pressure, the better your fuel economy. An infinitely hard tire would in theory have no rolling friction. As tires become softer, the friction goes up. You can generally overfill your tires 20% - 30% beyond its maximum rating without danger as long as the roads are not slippery. The pressure is often set in a range that allows for a comfortable ride with a big safety margin. You can use that margin to increase your fuel efficiency if you are careful about it.

So, the right speed and the right tire pressure are the most critical factors for fuel economy. Air conditioning also plays a part. Interestingly, if you require colder temperatures inside your car, your optimum fuel economy speed will be slightly higher than it would in a warmer car. However, your absolute economy will still be reduced. This is because the less time your car needs to work to cool the air, the less fuel is used. The harder your air conditioning has to work, the more importance this factor has on your fuel economy.

Hope some of these tips help.

[katabeachbum]

Many people make the mistake of thinking only the gear of your transmission matters in your fuel consumption, and that the higher the gear, the better off you are. This not true. Most cars actually have a dual peak in fuel economy, and the top gear may not be the best choice if your engine has to operate in the low 1000's in order to use it. The engine efficiency varies over the RPM range, and most engines generate their best brake specific fuel consumption at around 2700 - 3000 RPM. This means, that you get the most power per drop of fuel when your engine is running in this range.

Now, competing with this are inefficiencies from your transmission as it spins faster, as well as wind resistance from your car moving faster. If you had a 100% efficient continuously varying transmission, then your optimum profile would be to accelerate at about 3000 RPM until you reach your final speed, and then reduce the throttle to maintain that speed.

Even this isn't necessarily correct. A better method (but annoying as hell) is to actually drive at 3000 RPM until you hit the speed you want, then coast until your speed has bled off to the point Somchai's grandma is passing you, then accelerate again at 3000 RPM, rinse and repeat. The reason this works is because it allows you to operate your engine at absolutely the most efficient setting during every moment of your trip (the fuel used during idle has the effect of causing the best speed to reengage the engine to be higher than 0).

In practice, inefficiencies of various other components enter into the equation, which is why you see the effect above where accelerating improves fuel economy up to about 2000 RPM. It is important to know at what RPM your engine reaches its peak brake specific fuel consumption if you want the best fuel economy. You should target your acceleration about 200 RPM below this number.

The tradeoff between brake specific fuel consumption and wind resistance is also why cars have an optimal speed for travel (ignoring the pulse method above.) It is NOT true that 90 kph is always better than 100 kph. This number is very, very dependent on the Cd of your car. A very low Cd will cause the wind resistance curve to intersect the increasing efficiency of higher engine RPMs at a higher speed. My Altis 1.8 gets its optimum fuel economy at about 99 on the highway, at around 2200 RPM. Beyond this speed, the effect of wind resistance is greater than the increased fuel efficiency of the engine.

I bristle when I hear people say "90 is better than 100", because that is very dependent on your car. It may have been true 30 years ago when cars were shaped like boxes. It ain't true today. Every car has a different optimum speed based on its Cd and engine type, and in many modern cars that point is above 90, but I think it rarely goes above 105.

To the OP, if you want to find your optimum speed, you will need to make a very careful study over flat terrain for several hundred kms. driving carefully at many different speeds. Fill your tank, drive 200 km at one speed. Fill your tank again. Record the fuel used. Do this several times at the same speed and average the results to remove the effects of wind and small differences in how full you got your tank. Over a period of several months you can build a very accurate picture of how your vehicle performs.

Tire pressure is also extremely important in fuel economy. The higher the pressure, the better your fuel economy. An infinitely hard tire would in theory have no rolling friction. As tires become softer, the friction goes up. You can generally overfill your tires 20% - 30% beyond its maximum rating without danger as long as the roads are not slippery. The pressure is often set in a range that allows for a comfortable ride with a big safety margin. You can use that margin to increase your fuel efficiency if you are careful about it.

So, the right speed and the right tire pressure are the most critical factors for fuel economy. Air conditioning also plays a part. Interestingly, if you require colder temperatures inside your car, your optimum fuel economy speed will be slightly higher than it would in a warmer car. However, your absolute economy will still be reduced. This is because the less time your car needs to work to cool the air, the less fuel is used. The harder your air conditioning has to work, the more importance this factor has on your fuel economy.

Hope some of these tips help.

tyres

while increasing tyre pressure 20-30% over vehicle manufactorers recommended pressure, you may save 1-3% fuel, but you also reduce tyres lifetime with approx 50%. In addition you get much longer braking distance and reduced traction. Vehicles recomended tyre pressure as indicated in drivers doorsill provides max safety and lifetime.

vehicle manufactorers recommended tyre pressure is based on tyres traction and lifetime only, comfort is not considered. Comfort is created by choise of springs, shocks, rims, tyres and other suspension parts

[aussiebebe]

Many people buy eco cars with high expectations but driving style remains the biggest factor. I have long thought MPG ratings to be misleading as most cars can achieve around 30mpg at highway speeds: a V8 runs at so much lower rpm than an eco-engine that things balance out. In a city like Bangkok with so much idling and stop-start driving, what manufacturers should really be forced to display is the rate of fuel consumed whilst idling when every car achieves the same 0mpg efficiency.

[WarpSpeed]

Many people make the mistake of thinking only the gear of your transmission matters in your fuel consumption, and that the higher the gear, the better off you are. This not true. Most cars actually have a dual peak in fuel economy, and the top gear may not be the best choice if your engine has to operate in the low 1000's in order to use it. The engine efficiency varies over the RPM range, and most engines generate their best brake specific fuel consumption at around 2700 - 3000 RPM. This means, that you get the most power per drop of fuel when your engine is running in this range.

Now, competing with this are inefficiencies from your transmission as it spins faster, as well as wind resistance from your car moving faster. If you had a 100% efficient continuously varying transmission, then your optimum profile would be to accelerate at about 3000 RPM until you reach your final speed, and then reduce the throttle to maintain that speed.

Even this isn't necessarily correct. A better method (but annoying as hell) is to actually drive at 3000 RPM until you hit the speed you want, then coast until your speed has bled off to the point Somchai's grandma is passing you, then accelerate again at 3000 RPM, rinse and repeat. The reason this works is because it allows you to operate your engine at absolutely the most efficient setting during every moment of your trip (the fuel used during idle has the effect of causing the best speed to reengage the engine to be higher than 0).

In practice, inefficiencies of various other components enter into the equation, which is why you see the effect above where accelerating improves fuel economy up to about 2000 RPM. It is important to know at what RPM your engine reaches its peak brake specific fuel consumption if you want the best fuel economy. You should target your acceleration about 200 RPM below this number.

The tradeoff between brake specific fuel consumption and wind resistance is also why cars have an optimal speed for travel (ignoring the pulse method above.) It is NOT true that 90 kph is always better than 100 kph. This number is very, very dependent on the Cd of your car. A very low Cd will cause the wind resistance curve to intersect the increasing efficiency of higher engine RPMs at a higher speed. My Altis 1.8 gets its optimum fuel economy at about 99 on the highway, at around 2200 RPM. Beyond this speed, the effect of wind resistance is greater than the increased fuel efficiency of the engine.

I bristle when I hear people say "90 is better than 100", because that is very dependent on your car. It may have been true 30 years ago when cars were shaped like boxes. It ain't true today. Every car has a different optimum speed based on its Cd and engine type, and in many modern cars that point is above 90, but I think it rarely goes above 105.

To the OP, if you want to find your optimum speed, you will need to make a very careful study over flat terrain for several hundred kms. driving carefully at many different speeds. Fill your tank, drive 200 km at one speed. Fill your tank again. Record the fuel used. Do this several times at the same speed and average the results to remove the effects of wind and small differences in how full you got your tank. Over a period of several months you can build a very accurate picture of how your vehicle performs.

Tire pressure is also extremely important in fuel economy. The higher the pressure, the better your fuel economy. An infinitely hard tire would in theory have no rolling friction. As tires become softer, the friction goes up. You can generally overfill your tires 20% - 30% beyond its maximum rating without danger as long as the roads are not slippery. The pressure is often set in a range that allows for a comfortable ride with a big safety margin. You can use that margin to increase your fuel efficiency if you are careful about it.

So, the right speed and the right tire pressure are the most critical factors for fuel economy. Air conditioning also plays a part. Interestingly, if you require colder temperatures inside your car, your optimum fuel economy speed will be slightly higher than it would in a warmer car. However, your absolute economy will still be reduced. This is because the less time your car needs to work to cool the air, the less fuel is used. The harder your air conditioning has to work, the more importance this factor has on your fuel economy.

Hope some of these tips help.

tyres

while increasing tyre pressure 20-30% over vehicle manufactorers recommended pressure, you may save 1-3% fuel, but you also reduce tyres lifetime with approx 50%. In addition you get much longer braking distance and reduced traction. Vehicles recomended tyre pressure as indicated in drivers doorsill provides max safety and lifetime.

vehicle manufactorers recommended tyre pressure is based on tyres traction and lifetime only, comfort is not considered. Comfort is created by choise of springs, shocks, rims, tyres and other suspension parts

You're kind of contradicting yourself Kata as your second sentence is no longer applicable when the tires are no longer the originals. The premise of all working together though is something I've been trying to relate to racers for years without much success, they all work as a package and one thing changed will throw off the entire factory engineered balance which has to be compensated for by hours of testing to find the original balance. It is magnified even more when you throw in stress loads that the average street car will never see and then the alignment and other factors also come into play along with bushings and the like..

So to reiterate, a vehicles recommended tire pressures by the auto manufacturer is out the window once the original set of tires have been used unless you replace with exactly the same size diameter and brand tire in which case the next set of tires has to be pressurized accordingly and has to be determined by the owner. I would not leave that math to the tire installer who either was told a general tire pressure rating for all tires to keep it simple stupid or doesn't have a clue anyway due to a lack of education, face it that may seem harsh but the average tire guy is not the top of their class in any country, that's why a general rule of thumb of how much to add is necessary and is relative to the sidewall recommendations to be used as a guideline but not specific, which is why they are a general range from lowest recommended to the highest..

A low profile tire for example will require much higher pressures to properly support the tire side wall or else the same situation of all the deficits you mention will occur and cause premature tire wear and poor performance,fuel mileage, etc... They will be stiffer and that's the price you pay for a higher performance tire and not a comfy high sidewall tire..

Edited March 4, 2011 by WarpSpeed

[katabeachbum]

Many people make the mistake of thinking only the gear of your transmission matters in your fuel consumption, and that the higher the gear, the better off you are. This not true. Most cars actually have a dual peak in fuel economy, and the top gear may not be the best choice if your engine has to operate in the low 1000's in order to use it. The engine efficiency varies over the RPM range, and most engines generate their best brake specific fuel consumption at around 2700 - 3000 RPM. This means, that you get the most power per drop of fuel when your engine is running in this range.

Now, competing with this are inefficiencies from your transmission as it spins faster, as well as wind resistance from your car moving faster. If you had a 100% efficient continuously varying transmission, then your optimum profile would be to accelerate at about 3000 RPM until you reach your final speed, and then reduce the throttle to maintain that speed.

Even this isn't necessarily correct. A better method (but annoying as hell) is to actually drive at 3000 RPM until you hit the speed you want, then coast until your speed has bled off to the point Somchai's grandma is passing you, then accelerate again at 3000 RPM, rinse and repeat. The reason this works is because it allows you to operate your engine at absolutely the most efficient setting during every moment of your trip (the fuel used during idle has the effect of causing the best speed to reengage the engine to be higher than 0).

In practice, inefficiencies of various other components enter into the equation, which is why you see the effect above where accelerating improves fuel economy up to about 2000 RPM. It is important to know at what RPM your engine reaches its peak brake specific fuel consumption if you want the best fuel economy. You should target your acceleration about 200 RPM below this number.

The tradeoff between brake specific fuel consumption and wind resistance is also why cars have an optimal speed for travel (ignoring the pulse method above.) It is NOT true that 90 kph is always better than 100 kph. This number is very, very dependent on the Cd of your car. A very low Cd will cause the wind resistance curve to intersect the increasing efficiency of higher engine RPMs at a higher speed. My Altis 1.8 gets its optimum fuel economy at about 99 on the highway, at around 2200 RPM. Beyond this speed, the effect of wind resistance is greater than the increased fuel efficiency of the engine.

I bristle when I hear people say "90 is better than 100", because that is very dependent on your car. It may have been true 30 years ago when cars were shaped like boxes. It ain't true today. Every car has a different optimum speed based on its Cd and engine type, and in many modern cars that point is above 90, but I think it rarely goes above 105.

To the OP, if you want to find your optimum speed, you will need to make a very careful study over flat terrain for several hundred kms. driving carefully at many different speeds. Fill your tank, drive 200 km at one speed. Fill your tank again. Record the fuel used. Do this several times at the same speed and average the results to remove the effects of wind and small differences in how full you got your tank. Over a period of several months you can build a very accurate picture of how your vehicle performs.

Tire pressure is also extremely important in fuel economy. The higher the pressure, the better your fuel economy. An infinitely hard tire would in theory have no rolling friction. As tires become softer, the friction goes up. You can generally overfill your tires 20% - 30% beyond its maximum rating without danger as long as the roads are not slippery. The pressure is often set in a range that allows for a comfortable ride with a big safety margin. You can use that margin to increase your fuel efficiency if you are careful about it.

So, the right speed and the right tire pressure are the most critical factors for fuel economy. Air conditioning also plays a part. Interestingly, if you require colder temperatures inside your car, your optimum fuel economy speed will be slightly higher than it would in a warmer car. However, your absolute economy will still be reduced. This is because the less time your car needs to work to cool the air, the less fuel is used. The harder your air conditioning has to work, the more importance this factor has on your fuel economy.

Hope some of these tips help.

tyres

while increasing tyre pressure 20-30% over vehicle manufactorers recommended pressure, you may save 1-3% fuel, but you also reduce tyres lifetime with approx 50%. In addition you get much longer braking distance and reduced traction. Vehicles recomended tyre pressure as indicated in drivers doorsill provides max safety and lifetime.

vehicle manufactorers recommended tyre pressure is based on tyres traction and lifetime only, comfort is not considered. Comfort is created by choise of springs, shocks, rims, tyres and other suspension parts

You're kind of contradicting yourself Kata as your second sentence is no longer applicable when the tires are no longer the originals. The premise of all working together though is something I've been trying to relate to racers for years without much success, they all work as a package and one thing changed will throw off the entire factory engineered balance which has to be compensated for by hours of testing to find the original balance. It is magnified even more when you throw in stress loads that the average street car will never see and then the alignment and other factors also come into play along with bushings and the like..

So to reiterate, a vehicles recommended tire pressures by the auto manufacturer is out the window once the original set of tires have been used unless you replace with exactly the same size diameter and brand tire in which case the next set of tires has to be pressurized accordingly and has to be determined by the owner. I would not leave that math to the tire installer who either was told a general tire pressure rating for all tires to keep it simple stupid or doesn't have a clue anyway due to a lack of education, face it that may seem harsh but the average tire guy is not the top of their class in any country, that's why a general rule of thumb of how much to add is necessary and is relative to the sidewall recommendations to be used as a guideline but not specific, which is why they are a general range from lowest recommended to the highest..

A low profile tire for example will require much higher pressures to properly support the tire side wall or else the same situation of all the deficits you mention will occur and cause premature tire wear and poor performance,fuel mileage, etc... They will be stiffer and that's the price you pay for a higher performance tire and not a comfy high sidewall tire..

each vehicle model usually comes with at least 5 tyre options, and manufactorer recommends pressure for each of them, and for different loads if pressure adjustment needed. 65-45 profile tyres (as on 80% of all cars today) usually have same pressure

Takes approx 200k km for manufactorer/developer to establish correct tyre pressure

anyway, topic is about saving fuel. Higher tyre pressure saves some fuel, but comes at a cost of higher tyre costs and less traction, and reduced comfort

[WarpSpeed]

Like I said have not had much success explaining to anyone, just have to prove on the track or the road but the latter is nay on impossible to do so as it takes so long so I just let people remain stuck in their misguided ways. But have to point out the failure in the logic when they pass on the misguided info and let the concerned party discern for themselves.....

Edited March 4, 2011 by WarpSpeed

[transam]

Like I said have not had much success explaining to anyone, just have to prove on the track or the road but the latter is nay on impossible to do so as it takes so long so I just let people remain stuck in their misguided ways. But have to point out the failure in the logic when they pass on the misguided info and let the concerned party discern for themselves.....

Keep reading your post and cannot make head nor tail of it. NOT being negative but perhaps you can try again just for me. Really interested.

[WarpSpeed]

Like I said have not had much success explaining to anyone, just have to prove on the track or the road but the latter is nay on impossible to do so as it takes so long so I just let people remain stuck in their misguided ways. But have to point out the failure in the logic when they pass on the misguided info and let the concerned party discern for themselves.....

Keep reading your post and cannot make head nor tail of it. NOT being negative but perhaps you can try again just for me. Really interested.

Clue here is you need to read more then just THAT post to understand... In short it means the average person just doesn't get tire pressures and how they are supposed to be set and what a big difference the right pressures make in every aspect of a cars performance.. Even many who actually drive all out in race conditions don't have a clear idea of how it comes together to create top performance..

Edited March 4, 2011 by WarpSpeed

[corkman]

Switching off the air con entirely should save about 2-3 mpg.

Drive "smoothly" - i.e. pull away from the lights slowly, and when approaching lights ease off the gas as soon as possible and coast up to the lights.

Check the cars perfroamnce curve and when cruising, do so at the optimal speed (usually about 90kmh).

Avoid flooring it to pass something when on the high way - switch lanes and increase gradually to your desired speed, and creep past.

Eliminate weight - don't carry around anything more than you need to..... keep the boot and passenger spaces empty, and drive around with the tank half full rather than full i.e. in a typical week if you spend about 500 baht on fuel, then run it until nearly empty and then top up with 500 baht, rather than filling it up.

Do all these things and you'll probably save 10-20% on fuel.

Anicdotal evidence - back in the real world my old man drives his VW polo like this...... it is supposed to do about 40-45mpg but he gets 50-55+.

[transam]

Like I said have not had much success explaining to anyone, just have to prove on the track or the road but the latter is nay on impossible to do so as it takes so long so I just let people remain stuck in their misguided ways. But have to point out the failure in the logic when they pass on the misguided info and let the concerned party discern for themselves.....

Keep reading your post and cannot make head nor tail of it. NOT being negative but perhaps you can try again just for me. Really interested.

Clue here is you need to read more then just THAT post to understand... In short it means the average person just doesn't get tire pressures and how they are supposed to be set and what a big difference the right pressures make in every aspect of a cars performance.. Even many who actually drive all out in race conditions don't have a clear idea of how it comes together to create top performance..

Now l am going back 40 years, had my own Broadspeed Mini look a like. Stopped in a pub on route from a visit to the coast. This guy at the bar saw my ride and we started talking about stuff. Turned out he was a well known race car driver, he told me my tyre pressures were wrong. Hmmmmm l thought. So, put the pressures up to his recommendation, that week l wrote my ride off, autication with a lamp post while trying to sort out a Lotus Cortina.

The worse thing was the Ford guy didn't stop to pull me out, hate Ford guys.

[WarpSpeed]

What can I say? Some drivers just have problems with going fast and turning like chewing gum and walking I guess..

Edited March 4, 2011 by WarpSpeed

[MJP]

All of the above and . . . essential journeys only. Use GPS and route planning.

For business get everyone on Skype conference calling.

[WarpSpeed]

I'd say drive in a different country that doesn't run you Km out of the way with U-turns and back through crawling or in some cases static traffic just to get to your destination Km's back up the road again ...

It's really a metaphor for Thailand, run you in circles whenever it would be less stress and more efficient to go straight to the issues ..

Edited March 4, 2011 by WarpSpeed

[ClareQuilty]

Well, driving a car is best considered a luxury, not a necessity. I have a car but only drive it about once a week, to go to the neighboring large town about one hour's drive away. Around my smaller town I use a motorbike. If I go to Bangkok or other far-away destinations, I use the bus, which is still incredibly cheap in Thailand - one of the best deals remaining as the country gets more and more expensive.

Edited March 4, 2011 by ClareQuilty

[Lickey]

The best fuel saver is when the driver can feel the relationship between the engine and the road, , pull away in 2nd if there is a slight downhill advantage, or you can keep rolling, again, gear skiping if the vehicle has advantage of a high rev overtake in 3rd, go to 5th, and feather the pedal,

For me, its all about understanding the feel of the engine and the road, i see a red light, neutral and coast, come to a gentle stop on the brakes [cheaper than transmissions and clucthes] ok, air-con in slow city traffic, once out in the country, AC off and rear windows down, when parked, try not to use steering till moving, hydraulic steering pumps use fuel and increase tyre wear at a standstill,

Automatic drivers in the city can select 1/2/3 to suit the traffic conditions, the box wont go higher than you select, so when taking your foot off, it wont change up, even if you have peaked in that gear, again, you can get good MPG from an auto if have a good road/engine understanding.

[MJP]

Well, driving a car is best considered a luxury, not a necessity. I have a car but only drive it about once a week, to go to the neighboring large town about one hour's drive away. Around my smaller town I use a motorbike. If I go to Bangkok or other far-away destinations, I use the bus, which is still incredibly cheap in Thailand - one of the best deals remaining as the country gets more and more expensive.

Same as that but once a month for the truck and use a bicycle for the village (okay sometimes the scooter thing). Bus is perfect for long distance and so cheap.

Best fuel saving method is to use none at all, find alternative living strategies.

I still think Thailand is missing out by not importing at zero duty and no VAT these 90mpg diesel cars like the Vauxhall Corsa.