• Sep 10th 2009 at 3:58PM
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2010 Honda Insight - Click above for high-res image gallery

The faster you drive, the more fuel you use. Common sense, right? Absolutely, but it's still helpful to see real-life data, as you'll see by checking out the results of a recent test performed by Consumer Reports. Not all cars perform the same at various speed limits, and as you might expect, America's most fuel efficient models are also the vehicles most affected by higher speeds.

A total of seven vehicles were tested by CR: a Acura TSX with a 2.4-liter four-cylinder; a new 2010 Honda Insight; a Lexus RX350; a Mercury Mountaineer with 4.6-liter V8; Toyota Camry and RAV4 with 2.5-liter four-bangers; and a Yaris with a 1.5-liter four.

As you're probably aware, today's hybrids are optimized for high fuel economy at city speeds and therefore lose much of their miserly ways on the highway. As it turns out, this was especially true of the new Insight hybrid, which lost over 15 miles per gallon moving the needle from 55 mph to 75 mph – the largest drop in the contest. Click here for the complete test results.

[Source: Consumer Reports]

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    • 1 Second Ago
      • 6 Years Ago
      Some times the mpg measure can be misleading....

      I copied the values turned them in km/lt and then in lt/100 km (or 60 something miles) that provide a clear picture of how much fuel you spend for a specific distance.

      Consumption in lt/100 km are as follows:

      Make & model 55 mph 65 mph 75 mph
      Acura TSX 5.90 6.63 7.66
      Honda Insight 4.53 5.25 6.44
      Lexus RX350 7.61 8.58 10.23
      Mercury Mountaineer 4.6-liter V8 9.88 11.10 13.21
      Toyota Camry 5.84 6.74 7.89
      Toyota RAV4 6.80 8.03 9.08
      Toyota Yaris 5.53 6.21 6.92

      If we consider as benchmark the consumption at 55 mph the corresponding % are as follows:

      Make & model 55 mph 65 mph 75 mph
      Acura TSX 100% 112% 130%
      Honda Insight 100% 116% 142%
      Lexus RX350 100% 113% 134%
      Mercury Mountaineer 4.6-liter V8 100% 112% 134%
      Toyota Camry 100% 115% 135%
      Toyota RAV4 100% 118% 134%
      Toyota Yaris 100% 112% 125%

      So at 65 mph the Insight consumes only 16% more fuel per specific distance. This is comparable to the Camry and less than the RAV4. The least affected vehicles are the TSX, Mercury and Yaris with an increase of 12% whereas very good results are observed for the RX350.

      At 75 mph the Insight gets penalized by its small engine and consumes relatively more fuel than the rest of the flock. Still an increase of 42% is not that important compared to increases in the range of 30~35%.

      Another measure could be to calculated the amount of more fuel needed for covering the same distance at increased speed. This is maybe the most important measure for the average driver (how much will it cost me to cover 100 kms (or 60 miles)).

      These are the results

      Make & model 55 mph 65 mph 75 mph
      Acura TSX 0.00 0.73 1.77
      Honda Insight 0.00 0.72 1.91
      Lexus RX350 0.00 0.97 2.61
      Mercury Mountaineer 4.6-liter V8 0.00 1.21 3.33
      Toyota Camry 0.00 0.90 2.06
      Toyota RAV4 0.00 1.23 2.28
      Toyota Yaris 0.00 0.67 1.38

      These results are interesting.

      An increase of speed from 55 to 65 means that a Yaris will consume only 0.67 lt more of fuel thus for a distance of 60 miles the car needs 0.18 gallons of fuel more. This translates (for a 5$ per gallon price) to just 90 cents per 60 miles or 1.5 cents per mile more. The most interesting thing is that 2nd in this rank is the Insight with only 0.72 lt more of fuel. The mercury is the "worst" offender (the car that need the most additional fuel for an increase from 55 to 65) with 1.21 lt which translate i just 1.6$ more per 60 miles.

      An increase from 55 to 75 shows that the Yaris still excels (it needs only 1.38 lt more per 60 miles or just 0.37 gallons) with the TSX in 2nd position and the Insight in 3rd. Our "gas gussler" is the Mercury in need of 3.33 lt of fuel more per 100 kms or 0.88 gals per 60 miles.

      Since dollars and cents are important for a average mileage of 15,000 miles (24,100 kms give or take a few) the amount of fuel need is as follows (values in US gallons).

      Make & model 55 mph 65 mph 75 mph
      Acura TSX 376 423 489
      Honda Insight 289 335 411
      Lexus RX350 486 548 653
      Mercury Mountaineer 4.6-liter V8 631 708 844
      Toyota Camry 373 430 504
      Toyota RAV4 434 513 580
      Toyota Yaris 353 396 442

      In monetary terms just multiply these values to get the estimated cost of fuel. It is interesting to note that driving the Insight at 75 mph will result in less need for fuel than driving the RX350, Mercury or RAV4 at 55.

      So it all comes down to every indiviual's point of View IMHO.
      • 6 Years Ago
      No suprise.
      That pitiful little 1.3 is probably working overtime to keep the car moving on the highway.

      This is pretty typical of smaller motors though. They usually need really short gearing to keep them moving on the highway because of their lack of torque. It is probably turning 4000rpm or more. No motor is very efficient at that speed. Also, the hybrid system is not helping out so you're basically driving a heavy underpowered car with a strained motor. 3000lbs with a 1.3l engine... fail.

      Honda powertrains suck these days. They could be getting better fuel economy out of bigger motors like everyone else. I don't get it.
        • 6 Years Ago
        A "pitiful" little 1.3L is probably near WOT at 75 mph while still running closed-loop fuel control.
        i.e. energy loss at the throttle (pumping restriction) is minimized, thus maximizing net possible efficiency at that operating point.
        • 6 Years Ago
        It has a CVT, so the revs go up when you go uphill and/or hit a headwind, or turn on AC.
        When you are going downhill, the revs drop. Like 75mph@2500rpm

      • 6 Years Ago
      This is so true, at 75-80 mph on the freeway I can get Better fuel mileage out of my 5.7L Camaro in 6th gear than in my 1.5L CVT Civic.
      • 6 Years Ago
      Too bad the Prius/Jetta weren't included.

      A couple of points.

      A: The Insight still had the best mpg.

      B: This is really a case where you need to look at G/M or L/100KM or look at fuel burned in a set distance to get a real idea of the change. Lets say you did this for 100 miles:

      "Worse" result: Insight (100 miles, fuel burned)
      55mph 51.9mpg 75mph 36.5mpg - 15.4 mpg drop.
      1.93 gallons 2.74 Gallons
      Increased fuel usage from driving faster: 0.82 gallons.

      "Best" result: Mountaineer: (100 miles, fuel burned)
      55mpg 23.8mpg 75mph 17.8mpg - 6mpg drop.
      4.20 gallons 5.62 gallons
      Increased fuel usage from driving faster: 1.41 gallons.

      So in reality, fuel usage increases were not worse were this test claims, the were worse were the numbers initially look best and vice versa.
        • 6 Years Ago
        exactly, we keep seeing subtle calls for a gallon per mile standard in editorials here and there, it'd make a lot more sense.
      • 6 Years Ago
      I've never seen a difference that big in any of the cars I've owned from 55mph to 75mph. I've driven a mini-van, large sedan, compact sedan, and a wagon. I'd say the typical drop would be 10%, not 25%. Perhaps it's due to secondary factors. I.e., if I'm driving in a 55mph zone, I'm more likely to encounter traffic lights or other obstacles / drivers that require me to brake and re-accelerate.

      They didn't give any details of this test. Did they do it in a wind tunnel, on a test-track, on a closed highway? Did they burn through a full tank of gas?

      I'm skeptical.
      • 6 Years Ago
      It's a real shame Consumer Reports did not include a European car, especially a diesel, in their test. In my experience European cars do not loose nearly as much in fuel economy when driven at 75 mph or higher as they are designed to run at that speed or higher.
        • 6 Years Ago
        That's true. I drive a 118d 3 door and it's amazing the sort of figures you can get a high speed. On a 220 mile journey 90% of which was spent above 100mph that car still managed 30mpg (US). Diesels are amazing for high speed motorway driving.
      • 6 Years Ago
      I'd have to agree with another poster and say the real winner is the TSX. 30mpg at highway speed in a luxurious, attractive (minus the grill-face) and sporty midsize sedan is a pretty nice package overall.
      • 6 Years Ago
      I'd be curious to see how a slippery car with a V8 would do in this test, I'm guessing a Corvette running at 75 in top gear will have relatively low RPMs and produce much better results than the Mountaineer
        • 6 Years Ago
        That 5.7l V-8 is a thirsty animal, and 75 mph might not be fast enough.

        At 100 mph, the Corvette should win hands down against the rest of the pack, as they'll have to be turning big rpm with a wide throttle to maintain speed with their little engines.
      • 6 Years Ago
      Now TDIs? The whole reason they dominate in europe is they pretty perky and get great economy. Maybe that's why it was left out?
        • 6 Years Ago
        At 55, I get about 44 mpg.

        At 75, I get about 39 mpg.

        This is in a 1999 MkIII Jetta, not maintained as best as I should. I should borrow my mate's gadget so I can monitor it in real time while trying to keep my good eye on the road.
        • 6 Years Ago
        I don't have a TDI, but I'm sure that they would put impressive numbers. I think that you're right, they knew that diesel cars would do well on this test, that's why they were left out.
      • 6 Years Ago
      I've always wondered how much mpg is affected by different highway speeds.

      My 03 Accord V6 averages close to 31 mpg at 80 mph besting the 27 mpg rating. I'm curious now what I could achieve at lower speeds.
      • 6 Years Ago
      the insight is still much more fuel efficient than all of the other cars at any speed.

      the "biggest loser" is still the winner.
      • 6 Years Ago
      "The faster you drive, the more fuel you use. Common sense, right?". No, not right. It is not "common sense". The "common secnse" says that regardelss of the speed the fuel usage (im mpg) remains constant. Sure, you use more fuel per minute, but at the same time you get to your destination faster by the same factor. The net effect is zero.

      What makes the fuel usage increase with speed (after a certain limit) is the quadradic growth of drag with relation to speed in case of turbulent airflow. And the boundary speed, after which the drag starts to grow very fast, depends on the aerodynamic properties of each particular car. The popular "55 mph" value is just a random average, which has as much meaning as the average temperature of every human body in a hospital.

      Anyway, this is not "common sense". This is rather complicated physics.
        • 6 Years Ago
        you know we are talking about miles per gallon, right? it's not minutes per gallon. the time to complete the trip is not part of the equation.
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