Does SUV cars generally consume more fuel than sedan cars ? Especially at high speeds (more than 60 km/h).
If yes, is the difference significant ?
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Generally speaking, SUVs get worse fuel mileage than a sedan with everything else being the same (yah, like that would ever happen). I agree with the other statements about the frontal area of the vehicle causing wind resistance at higher speeds, but there's another factor which hasn't been mentioned yet and that being the space between the vehicle and the ground (ground clearance).
Most SUV's are set higher in the air for ground clearance. This provides more maneuverability in uneven terrain in off-road situations and when traversing through snow. The unfortunate side effect of this is there is more of the underbelly showing and air can get between the ground and the vehicle. This creates a HUGE amount of wind resistance as the underside of the vehicle is anything but smooth. Sedans, being much closer to the ground, have less air under the vehicle so have less to resist. This creates a much smoother transition through the air even as speed increases. Some sedans (and many sports cars) can have a frontal design which forces much of the air to the sides and over the car, which can actually create a slight vacuum under the vehicle. This lack of air reduces wind resistance even more, which can produce even better fuel mileage results.
Needless to say, the slicker the vehicle (the better it can cut through the air), the better it will do on fuel mileage. As a vehicle's speed increases, the resistance on the vehicle grows exponentially. The less resistance on the low end of the speed chart, the slower that resistance is going to climb when moving. Let's face it, most SUVs are bricks in comparison to their sedan counterparts. There's almost no way to get around it: in most cases you'll get worse fuel mileage from an SUV than you will a sedan.
Please note: there are some exceptions. There are some smaller SUVs which have hybrid packages installed on them (like the Escape Hybrid). These vehicle can get better fuel mileage than a normal sedan, but comparing them to a hybrid sedan, there really isn't a comparison. The SUV is still going to lack in the mileage department.
Let's face the facts, though: you don't buy an SUV if you're worried about fuel mileage. You buy one for those other factors like I've mentioned and many more.
This depends on so many factors that it's impossible to answer in a way that is applicable to all situations.
I used to have a 1989 Opel Vectra sedan with 115hp 2.0-litre engine. Consumption? 7.7 litres per 100 km according to the fuel consumption standard back then, and I would say I generally got about 8 litres per 100 km.
Now I have a 2016 Toyota RAV4 hybrid SUV with 197hp 2.5-litre engine with electric boost (included in the 197hp figure, without it it's only 155hp). The official consumption is 5.0 litres per 100 km according to the current fuel consumption standard, but in practice it consumes 6.5 litres per 100 km.
Between the RAV4 and the Vectra, I had a very small hatchback, 2011 Toyota Yaris, with equal consumption figures (both official and practical) with the RAV4.
So, as you can see, technology can definitely reduce the fuel consumption of vehicles. The question therefore is how much more advanced the technology on the SUV is compared to the technology on the sedan.
All things being equal, the SUV has more frontal area (greater air resistance) and higher weight (greater rolling resistance and greater energy requirement for acceleration). The greater energy requirement for acceleration means two things: to have similar acceleration, higher engine power is needed which causes more consumption when driving at constant speed, and also the fuel going to the acceleration will also obviously be consumed, typically in a way that it cannot be restored when braking (an exception to this would be obviously hybrids).
To make the situation more complicated, SUVs are often all-wheel drive. This means higher consumption with standard technology, but then again the rear wheels are increasingly often driven by an electric motor on demand, which doesn't increase fuel consumption in the typical operation mode (only front wheels powered).
My answer is that you want to pick a SUV you could consider buying, and pick a sedan you could consider buying, and compare their consumption figures. Don't think that SUV would always have higher consumption.
Paulster's answer nicely covers the aerodynamics aspect and while aerodynamics are almost certainly the biggest factor at a steady speed, especially at higher speeds (think > 50mph) it's not the only thing to consider in the overall fuel consumption figures. SUVs are (typically) heavier than sedans which will lead to higher fuel consumption during acceleration. Similarly SUVs are more likely to be 4WD than sedans and this leads to efficiency losses as a result of driving the differentials/transfer box. Both of these factors will heavily impact fuel consumption during driving that features a lot of stop-start such as in urban environments.