Hypermiling - fuel efficiency taken too far?

[bluebox_rob]

This is an interesting article profiling the 'Most Fuel-Efficient Driver in the World':
http://motherjones.com/politics/2007/01/guy-can-get-59-mpg-plain-old-accord-beat-punk.

Some interesting techniques, and some overlap with more traditional advanced driving, but at times the fuel efficiency seems to come at the expense of a little safety - would be interested to hear what people think about it!

[Astraist]

I too believe that fuel efficiency can be taken too far. I also believe that when it is taken too far as to compromise parameters like safety, it will also eventually prove inefficient because the fuel efficiency might be reduced by the increased wear and tear on car parts.

Perhaps the best example as it appears in the article is not using the A/C. I live in a very hot country where not using the A/C is a pure compromise on safety and even the passengers' health. Also, the increased fuel efficiency will be more than canceled since not using the air conditioning causes premature leaks due to crazing in the rubber bands (which get lubricated as the gas is circulated inside the system).

Another popular example is entering the low-pressure area behind lorries. Other than an immense compromise on safety when it comes to following distances, it turns out that the distance you actually need to maintain in order to benefit from such driving is about very few feet, especially with newer lorries and buses which are build with aerodynamics in mind (being often as aerodynamic as some bikes! ) and will again be more than canceled since following so closely would cause frequent alternation of throttle pressure and even closing it all together and braking and accelerating again.

Driving too slowly to the conditions which will also reduce the ventilation of the oilpan and engine (mainly the crankcase) and reduce soot deposit burning away, driving on very high tyre pressures which will increase tyre and damper wear, and other methods - are all inappropriate.

[shan0105]

The goals of hypermiling are positive, such as eliminating aggressive driving and saving energy. Unfortunately, some motorists have taken their desire to improve fuel economy to extremes with techniques that put themselves, as well as their fellow motorists, in danger.

Nowadays, many people are now doing hypermiling. In fact, an Australian couple has just set a brand new planet record for “hypermiling,” or pushing a car’s limitations for fuel efficiency. From the article "Couple uses Passat TDI to set 84 mpg hypermiling record," John and Helen Taylor, who have been at hypermiling for some time, drove a Volkswagen Passat TDI 1,626 miles on one tank of diesel fuel, setting a record in the U.S.

Hypermiling techniques are not limited to driving style. How motorists maintain their vehicles is also key in reaching optimal fuel economy, but extreme measures can be harmful to a vehicle.

However, there are several safe and legal driving techniques motorists can implement to conserve fuel, such as smooth and easy acceleration and braking, maintaining a steady speed, using cruise control and looking ahead to anticipate changing traffic conditions.

[martine]

Hi shan105 and welcome!

So do you use the more extreme techniques? Have you seen the thread discussing whether it is indeed best to accelerate gently (for a longer period) or briskly (for a shorter period)? I don't think anyone's come up with a definitive recommendation yet.

[Horse]

just set a brand new planet record for “hypermiling,” or pushing a car’s limitations for fuel efficiency. From the article "Couple uses Passat TDI to set 84 mpg hypermiling record," John and Helen Taylor, who have been at hypermiling for some time, drove a Volkswagen Passat TDI 1,626 miles on one tank of diesel fuel, setting a record in the U.S.

Worth noting that . . .

The imperial gallon was originally defined as the volume of 10 avoirdupois pounds of water under specified conditions. The imperial gallon (4.54609 litres (L)) is 20% larger than the United States liquid gallon (3.785411784 L). The imperial bushel (36.36872 L) is 8 imperial gallons and is about 3% larger than the US bushel (35.23907016688 L).

The subdivision of the imperial gallon in British apothecaries' fluid measure differed in two important respects from the corresponding United States subdivision: the imperial gallon was divided into 160 fluid ounces, the United States gallon into 128 fluid ounces; and a "fluid scruple" is included.

These differences come from the various systems that were in use in Britain when the first colonies in North America were established. The American colonists adopted the English wine gallon of 231 cubic inches (3.78541178 litres), and used it for all fluid purposes. The English of that period used this wine gallon, but they also had the ale gallon of 282 cubic inches (4.62115205 litres). In 1824, the British adopted the British imperial gallon, defined as the volume of 10 pounds of water at a temperature of 62 °F, weighed in air with brass weights, by calculation equivalent to about 277.42 cubic inches (4.5461 L)—much closer to the ale gallon than the wine gallon. At the same time, they redefined the bushel to be 8 gallons.

Even under the new imperial system, wine volumes continued to be measured in the old 231-cubic-inch wine gallons (3.78541178 litres) for tax purposes, and this practice continued until the late 1990s.

As noted above, in the imperial British system the units of dry measure are the same as those of liquid measure. In the United States these two are different: the gallon and its subdivisions are used in the measurement of liquids, the bushel and its subdivisions in the measurement of certain dry commodities. The US gallon (3.785411784 L) is divided into four liquid quarts (946.352946 mL each) and the US bushel (35.23907016688 L) into 32 dry quarts (1.101220942715 L) or 4 pecks (8.80976754172 L). All these units of volume for liquid measures are about 20% larger in the imperial system than in the US system. However, the British fluid ounce is only about 96% of the US fluid ounce because there are 40 fluid ounces in the British quart but only 32 fluid ounces in the US quart.

In the imperial system an avoirdupois ounce of water at 62 °F (16.67 °C) has a volume of one fluid ounce, because 10 pounds is equivalent to 160 avoirdupois ounces and 1 imperial gallon is equivalent to 4 imperial quarts, or 8 pints. This convenient fluid-ounce-to-avoirdupois-ounce relation does not exist in the US system because a US gallon of water at 62 °F weighs about 8 1⁄3 pounds, or 133 1⁄3 avoirdupois ounces, and the US gallon is equivalent to 128 fluid ounces.

In the apothecary system of liquid measure the British add a unit, the fluid scruple, equal to one third of a fluid dram between their minim and their fluid dram.

One noticeable comparison between the imperial system and the US system is between some Canadian and American beer bottles. Many Canadian brewers package beer in an 12-imperial-fluid-ounce bottles, which are 341 mL each. American brewers package their beer in 12-US-fluid-ounce bottle, which are 355 mL each. This results in the Canadian bottles being labelled as 11.5 fl.oz in US units when imported into the United States. Because Canadian beer bottles predate the adoption of the Metric System in that country, they are still sold and labeled in Canada as 341 mL. Canned beer in Canada is sold and labeled in 355 mL cans, and when exported to the US are labeled as 12 fl. oz.

http://en.wikipedia.org/wiki/Comparison ... nt_systems

And then we move on to a pound of gold weighing more that a pound of lead . . .

[Kevin]

On a recent 300-mile journey, about half on dual carriageways and half on single carriageway A-roads, my little 1.6 TDi Fiesta manages about 60mpg (at least, according to the computer display). This is with me driving up to the legal limit and with brisk acceleration.

As an experiment, I once completed a 90-mile journey mainly on single carriageway A-roads, but I followed heavy goods vehicles whenever possible to try to benefit from their slipstream. Although I was a lot closer than the usual 2-second gap, I didn't consider it particularly dangerous. The speeds were in the 40 to 50 mph region and lorries tend not to stop on a sixpence. The thing that concerned me most is that I was potentially creating a more difficult overtake, as anyone wishing to do so would have to pass me and the lorry I was following, so I would occassionally drop back if someone looked like they wanted to pass.

The 90-mile journey was completed with a fuel consumption figure of, coincidently, 90mpg. Was it worth it? Not for me. I was bored stiff and I found it tiring having to concentrate on the back of the lorry with little other visual sensory input. An interesting experiment, but not one I'd be repeating.

[michael769]

The speeds were in the 40 to 50 mph region and lorries tend not to stop on a sixpence.

I would not rely on that! The thing to consider is it's brakes are designed to stop 44tonnes. If the truck is unladen it will be considerably lighter and will be able to pull up in a much shorter distance than most cars.

I remember the first time I drove a large truck - I nearly went through the windscreen the first time I touched the brakes!

[Gareth]

One aspect about the reference report that stood out for me was that they were driving about 14 hours a day, which means that nearly all of the journey would have been when the engine was at normal operating temperature.

When I've driven during the rush hour, I'm finding that the VAG TDi engine in our car takes an age to get up to normal temperature, during which time the consumption is much higher. Less so in the summer, of course, so I imagine a warmer climate might be a benefit as well.

[Kevin]

The speeds were in the 40 to 50 mph region and lorries tend not to stop on a sixpence.

I would not rely on that! The thing to consider is it's brakes are designed to stop 44tonnes. If the truck is unladen it will be considerably lighter and will be able to pull up in a much shorter distance than most cars.

I remember the first time I drove a large truck - I nearly went through the windscreen the first time I touched the brakes!

I was thinking more that the drivers tend not to stop their lorries that quickly, rather than a problem with the efficiency of the brakes. Lorries can stop reasonably quickly, I should know, I still drive a 44-tonner occassionally.

[michael769]

I was thinking more that the drivers tend not to stop their lorries that quickly,

They do in a pile up.

Personally I would not be comfortable driving close behind something I could not see around!

[Kevin]

I was thinking more that the drivers tend not to stop their lorries that quickly,

They do in a pile up.

Personally I would not be comfortable driving close behind something I could not see around!

Very true, it's not comfortable driving close behind, which is why I won't be doing it again.

[Astraist]

The benefit from following up behind big lorries is not very significant unless you follow them extremly close up and personal. Modern lorries and buses in particular are designed to generate less drag and thus less "slip stream." Anyhow, whatever you might save from driving close behind a lorry, is lost in the very first time that the lorry brakes.

If you hang further back, your own deceleration could be more gentle than that of the car ahead. Also, you are able to see past it and generate observation that could help you anticipate the need to slow down before them, increasing the benefit in gas consumption even more.

I would not go (methodically) for anything under two seconds, for any reason.

They do in a pile up.

In that situation, even a safe margin will not avail (since the lorry will be stopped by the collision with the car ahead). The solution: Trying to see past the car ahead and slow down even earlier than them coming up to hazards and also considering a possible escape route should the braking distance not suffice. The same applies for cars that carry cargo which might drop off of them.

[Horse]

If you hang further back, your own deceleration could be more gentle than that of the car ahead. Also, you are able to see past it and generate observation that could help you anticipate the need to slow down before them, increasing the benefit in gas consumption even more.

It's shocking how far some drivers don't look ahead . . .

A few days ago, on the motorway while heading to work, I was already slowing - very gently, just easing off the throttle - as I'd seen several sets of brake lights ahead (a few hundred yards, at least, but clearly visible), and other drivers were passing me and actually accelerating towards the obstruction . . .

[exportmanuk]

It's shocking how far some drivers don't look ahead . . .

A few days ago, on the motorway while heading to work, I was already slowing - very gently, just easing off the throttle - as I'd seen several sets of brake lights ahead (a few hundred yards, at least, but clearly visible), and other drivers were passing me and actually accelerating towards the obstruction . . .

Most drivers look as far as the vehicle in front of them, I think that is why so many drive through red lights. They have not seen them they have tunnel vision totally focused on the brake lights of the car they are following.

I have a 06 petrol Mondeo auto mostly used for long distances on the motorway. if I stick at around 60 MPH I can get over 40 MPG at 70 around 36 at 80 it drops to 33 after that it falls through the floor. But I find driving at 60 in free flowing traffic mind numbingly boring.

[speeddemon]

Wow! 59 MPG, that is great but do you think it's worth it? its kinda dangerous for me.

+1 for that guy.