Extreme fuel economy: how green could your car get?

Extreme fuel economy: how green could your car get?Steve Walkercontent editor, MSN Cars2012-08-09T09:46:35Like it or not, these days a car's efficiency is as important as the way it looks or how fast it goes. Where once car-buying decisions were made through showroom drooling and test drive throttle stomping, now we're more likely to take the spec sheet home and feed the mpg and CO2 data into a spreadsheet.Carmakers, of course, know this and are pushing ever harder at the boundaries of how many miles their products can eek from a gallon of fuel. It's an economy drive that will continue as long as car buyers are happy to pay through the nose for the latest super-efficient engine or green technology breakthrough.In some ways it's sad but it's also understandable. Nobody wants to spend more than they have to on running a car, but we wondered: is shelling out for the latest, greenest vehicles really money well spent?It's a fact that the number of miles per gallon we achieve can have less to do with the car we drive and more to do with how we drive it.To see just how much difference the driver can make to a car's fuel consumption we dreamed-up a little, non-scientific experiment to take us from one fuel economy extreme to the other.How green could our car get?The aim of the game was simple, take one fairly ordinary family car and drive it over the same route in two completely different ways. First, trying to achieve the most dismally disappointing fuel economy returns we possibly could and then pulling out all the stops to drive in a super-efficient manner, green enough to see us installed on Bill Oddie's Christmas card list.Our sled for this non-scientific expedition to the two distant poles of fuel economy was Volkswagen's Golf GTD, a sporty, five-door family hatch with a 168hp 2.0-litre diesel engine.On the official fuel economy tests, carried out on a rolling road in laboratory conditions, this Golf returns 43.5mpg on the urban cycle, 65.7mpg on the extra urban cycle and 55.4mpg on the combined cycle. That's a strong performance by the car's modern common-rail direct injection diesel engine, which can also help the GTD to a 138mph top speed and a 0-60mph sprint of 8.1s.Top 10 most economical carsMSN Cars Green Car Guide The bad fuel economy run - what we didIt isn't hard for any car to consume fuel at a rate normally associated with a fire at an oil refinery. You could drive everywhere in first gear, the rev-counter needle quivering on the red line, and bung a couple of axle-buckling boulders in the boot but you'd destroy your car in pretty short order. This wasn't our aim.We were looking to try and replicate the kind of inefficient driving habits we all lapse into from time to time, showing how much of a negative effect a combination of these things can have on fuel economy. To make the engine work hard we needed to add weight and do our best to scupper the slippery aerodynamics that Volkswagen's engineers spent countless hours in a wind tunnel perfecting. Just as countless families do every year when they head off on holiday, we added a roof box to the top. Although, rather than beach towels, buckets and spades, we loaded in two bags of gravel.Even more weight came courtesy of a couple of back-seat passengers and a boot full of luggage, including two large hold-alls, a few more bags of gravel and a rather sorry-looking pot plant for good measure. The Golf was some way shy of being overloaded but it was sitting noticeably lower on its suspension, laboring under the kind of weighty cargo that we all subject our cars to from time to time. Almost everyone reading this will have stuff cluttering up their car that doesn't need to be there.To upset the Golf's aerodynamics further on our bad economy run we opened all the windows. Then we cranked up the air-conditioning and any other electrical systems that fell to hand, adding more to the engine's workload.Real-world mpg: the biggest car fuel economy losers  The bad fuel economy run - how it wentThe Golf was already set up for a spectacular fuel economy fail but out on the road we wanted to drive it in the wrong way too.Our 53-mile route included motorway, winding country roads and urban areas. We set about driving it in a jerky, inefficient manner - accelerating too hard, holding each gear up to the rev-limiter and braking late with little thought given to maintaining the car's momentum at junctions or traffic lights.It quickly became clear that this wasn't going to be a pleasant experience. The Golf's handling wasn't helped by the extra weight on board. You could feel the load transferring around as the car changed direction and leaned into corners. The edge was taken off its acceleration too, even with the GTD's muscular 258lb/ft torque output.More than anything, the inefficient driving style makes any journey more uncomfortable and stressful for passengers and driver. The noise from the over-revved engine and the sharp braking/acceleration were enough to make anyone feel a bit green and our back-seat guinea pigs also had the open windows and blasting air-con to put up with.With the route completed, the Golf's trip computer told a tale of woe. The 53-mile round trip had taken 1hr 12mins at an average speed of 44mph. But...drum roll please... the average fuel economy was a scandalous 30.8mpg. That's worse than the official combined cycle figures for Porsche's 400hp automatic 911 Carrera S Cabriolet. Not good.Bing map: extreme fuel economy test route  The good fuel economy run - what we didNow, we were sure the Golf could do better so it was time to drive the same route again with all the unnecessary gubbins stripped away and a different driving approach.We got the weight down to a minimum, losing the roof box and the peaky-looking passengers in the process, tightened up the aerodynamics and turned off the in-car electrical systems we didn't need. Crucially, this time we were going to aim to drive as efficiently as possible, smoothness and anticipation would be our new best friends. How green could we go?The greenest cars on sale  The good fuel economy run - how it wentDriving greener largely boils down to common sense and anyone can do it. A quick scan of the internet before we set off on our second run revealed a slew of economy driving tips, most of which you could have guessed anyway.In a nutshell, you want to use the engine smoothly and sparingly, then once you've gained momentum, the trick is to keep it. By looking up the road and predicting what's going to happen ahead, it's easy to keep the car rolling and minimise fuel-sapping starts and stops.The net result of this more considered driving style isn't just a healthier-looking fuel gauge. It's a far more relaxing experience for everyone on board. If the back-seat passengers hadn't been left to entertain themselves back at base, they'd have appreciated the low engine noise that comes from a firm but steady use of the throttle and early selection of the next gear. By looking ahead and trying to stay off the brakes, the ride gets smoother still.The Golf even handled better without its cargo, tucking into corners more easily and rounding them with less body roll. If you imagine that economy driving involves being overtaken by elderly cyclists and constantly having a tailback of irate motorists gesticulating furiously in your rear-view mirror, think again. On country roads, you can build speed and keep it by placing the car well through corners cutting your use of the brakes. It's hugely more comfortable and can be a lot more fun.The cars that go farthest on a tank of fuelBing map: extreme fuel economy test route  Extreme fuel economy - the resultThe second run completed, it was time to take stock and mull over the results.Our good economy run did take longer, a 1hr 22min journey time means a difference of 10 minutes. The average speed dropped from 44mph to 39.2mph too but again, that's not a big difference. Varying traffic conditions on our two runs mean you can't read too much into numbers this close anyway.What does warrant a few hoisted eyebrows is the difference in fuel economy between our bad and good economy runs. The 30.8mpg we got on the bad economy run made us realise why they have those tissues on the garage forecourts. By contrast, when we lost the weight, improved the aerodynamics and drove the Golf more economically, the car responded with an excellent 62.8mpg.We clearly pushed things to extremes but not so far as to make the test unrepresentative in the real world. Our results clearly show that a car's fuel economy depends massively on what you carry in it and how you drive it. Extreme Fuel economy - results Bad economy runGood economy runRoute distance53 miles53 milesTime1hr 12mins1hr 22minsAverage speed44mph39.2mphAverage fuel economy30.8mpg62.8mpgCar - Volkswagen Golf GTD 5drEngine2.0 TDI common-rail dieselPower/torque168hp/ 258lb ftPerformance: Top speed/0-60mph138mph/8.1sOfficial fuel economyUrban - 43.5mpg Extra-urban - 65.7mpg Combined - 55.4mpgWhat's the best average fuel economy you've achieved in your car? What are your top economy driving tips? Let us know in the comments section below...Bing map: extreme fuel economy test routeMany thanks to Thule for the loan of the roof boxHow to save fuel - green driving tipsTop 10 most economical carsMSN Cars Green Car GuideReal-world mpg: the biggest car fuel economy losersThe cars that go farthest on a tank of fuelThe greenest cars on saleCars that avoid road taxseo_keywordsfuel economy250864175http://cars.uk.msn.com//features/green-motoring/images.aspx?cp-documentid=250864175