KEY POINTS:
High fuel prices are inspiring motorists to come up with all sorts of hare-brained ways to drive more economically. That has prompted a warning from the AA that safety matters more than cutting your fuel bill.
In the US, growing interest in squeezing the last drop out of
the petrol tank can be seen on the web, with numerous sites popping up where people trade tips and boast about how many miles per gallon they're getting. In a country not famous for energy conservation, driving economically has become like a new extreme sport with a fervour and burgeoning language all of its own.
Adherents are known as "hypermilers", a term first used when hybrid petrol-electric cars became available and owners sought ways of making them go further. "Surge and glide" - speeding up then coasting - was one technique they devised. There are numerous others. Coasting down hills ("forced auto stop", or FAS, in hypermiler-speak), drafting, turning the engine off and coasting into park, backing into a park that you can later roll out of, over-inflating your tyres and driving on the white centre line are all suggested ways of eking out your tankful.
But many are downright dangerous. Drafting is what cyclists do while riding in a bunch. The leaders do the donkey work of pushing into the wind while those behind take advantage of the reduced wind resistance.
It's risky enough on a bike but, in a car doing 100km/h, with no distance between you and the truck or other large vehicle you're drafting, it is hazardous in the extreme.
Similarly, inflating your tyres beyond their recommended pressure might reduce rolling resistance but, with less rubber on the road, it also reduces traction. Meanwhile, the riskiness of "ridge riding", with one set of tyres on the smooth centre line, should be obvious to anyone.
Even coasting down hills with the engine off, popular with petrol misers during the lean post-war years, is asking for trouble - ever tried using power-assisted brakes and steering without the motor running?
The AA is increasingly being asked by motorists for fuel saving advice. But technical services general manager Stella Stocks gives the thumbs down to most of the techniques on that list. However, she says other hypermiler favourites, such as choosing a route that minimises stopping and starting, and slowing to let lights turn green, make sense.
The key to saving fuel is driving smoothly, she says.
"If you're not accelerating harshly and not having to brake harshly then you're going to get a more fuel-efficient outcome." If you have passengers, they'll have a more comfortable ride, as well.
Stocks says a regularly serviced vehicle also helps (hypermilers recommend using thinner oil), including ensuring tyres are at the correct pressure. Limiting use of air-conditioning will also save fuel.
Smooth acceleration matters as much for hybrids as it does for petrol and diesel vehicles, she says, because a hybrid's petrol engine takes over when driven hard.
Switching off the engine when held up at an accident scene, say, can be a good idea but, for safety reasons, Stocks wouldn't recommend it when in stop-start motorway traffic.
Car makers are both helping and hindering the drive to use less fuel. On the one hand, modern cars go faster than ever, tempting drivers to put their foot down. But on the other, fuel economy is increasingly a vehicle selling point.
Stocks says the AA is trying to encourage manufacturers to build more fuel-efficient cars with minimal CO2 emissions through its annual motoring awards, which have begun to factor those elements into the scoring.
Volkswagen won the AA's inaugural environmental award last year for its BlueMotion range of diesel Passats, Golfs and Polos, which are claimed to be highly economical - in part through improved aerodynamics - and clean-running.
Another approach car makers are taking to fuel saving is building engines that partly shut down when under light load. Honda's new Accord V6, for instance, runs on six, four or three cylinders, depending on how hard it is working.
New "automated manual" transmissions - such as VW's Direct Shift Gearbox, made by BorgWarner - that use software and electronics to change gear and operate the clutch much more quickly and smoothly than the driver could are also credited with improving fuel economy.
Hardcore hypermilers, it would seem, are willing to try anything to get more miles per gallon. Some describe doing their own vehicle modifications to reduce drag.
They even suggest driving to music with a slow tempo. Perhaps the best idea of all is the least obvious - try to drive less. If that's not an option, Stocks says the AA's advice is clear: don't put eco-driving before safe driving.
Hyper Economy
* The so-called "king of the hypermilers", American Wayne Gerdes, has claimed 84 miles per gallon (2.8l/100km) from a standard-issue Ford pick-up, and better than twice that driving a hybrid Honda Insight.
* Hypermiling techniques range from the obvious (driving more slowly, avoiding abrupt acceleration), to the technical (over-inflating tyres, thinner oil), to the downright dangerous, such as driving in the slipstream of larger vehicles.
Anthony Doesburg is an Auckland technology journalist
