Prius loses out to VW on Autoweek mileage test

In some circumstances, even my heavy, chunky , 4WD Volvo XC70 185hp diesel car can easily outperform my Prius in terms of fuel efficiency. All I have to do is drive both cars at 100mph (160km/h).

Diesels are known to be much more efficient than gasoline engines when they are heavily loaded. That's also why real-world fuel consumptions and test results are closer to the EPA numbers for diesels than for most gasoline cars.

It's biassed to test a Prius against another car on the highway only. The prius is at it's worst here, whereas a diesel is at it's best.

Also, never forget that it takes almost 20% more raw fossile oil to produce the same amount of diesel as it takes for gasoline...

 

To be honest, there doesn't seem to be much rhyme or reason to the mileage I get on my Prius.

Sometimes when I'm driving full speed on the highway (~70), I'm getting 80 mpg or more for 30 minutes or more. Sometimes the same road will give me ~40 mpg instead. My driving habits don't change that much, nor does the temperature here.

So I do believe that this test could have this result. However, if they do the same test again, they will likely have the Prius on top. This is why the scientific method demands that tests have repeatable and predictable results. After they've done the test thirty more times and have worked out some averages, then we can talk.

As for some people being anti-Prius, it is a little weird I agree. I'm not sure how such a car could offend anybody, but it does. We're living in some very strange days.

 

<div class='quotetop'>QUOTE(gippah @ Apr 23 2006, 12:10 PM) [snapback]243978[/snapback]</div>

headwinds? remember wind is a vector. a side wind will look like a quartering head wind. do the trig.

 

Consumer Reports is an excellent resource because they test their cars over several thousand miles and they do so in a consistent manner. They may be lead-footed, but that's good as their results basically show the minimum you can expect through reasonable driving habits.

On a 150-mile trip mostly over highway, CR got:

41 mpg with a 2006 Jetta TDI DSG (automatic)
48 mpg with a 2005 Prius
45 mpg with a 2006 Civic Hybrid

Also, the data on fueleconomy.gov shows:

41.7 mpg for the 2006 Jetta TDI (DSG automatic)
40.9 mpg for the 2006 Jetta TDI (manual)
47.3 mpg for the 2006 Prius
47.5 mpg for the 2005 Prius
44.7 mpg for the 2006 Civic Hybrid

So I can't understand how people argue the TDI gets better mileage.

 

I don't put much faith in the mileage that some magazine's "testers" get when they drive a car. Traditionally, I've generally gotten somewhere in the middle of the two EPA figures. With a Saturn SL1 that I had back in the nineties, I got 32 easily. With my Corolla, I got 34-36. The Prius has been a different experience in many respects but I'm currently getting 55-56 which is pretty much in the middle and I'm pretty sure that I'll get it up to closer to 60 this summer.

Coworkers and friends know what I'm getting because they always ask. I don't know what the motive behind some automobile magazine is for coming up with a "test" like the one that prompted this thread but a lot of the people that I know are aware of my mileage and that is much more "real world" than a magazine's article with problematic results. The Prius is very different from any other car (save for the Civic hybrid and the Insight) and it takes some learning. However, the mileage you're supposed to get is what I get and a guy who writes for a magazine but drives a "regular" car normally doesn't get what I'd call "real world" results.

 

With the last several cars we have driven (Ford Festiva and Chevy Metro most recently) we have gotten above EPA ratings. This is no doubt because we drive below 70 in those little rattle traps and have always slowed gradually to stops and turns and didn't accelerate aggressively (well how could you with those itty bitty engines).

Those driving habits have generally served us well, about 3,000 miles in to our new Prius. We are getting consistently above 50 mpg now that winter has released, in almost exclusively highway driving. Where we see inconsistencies in mileage there is always, it seems, a headwind involved. Even though areodynamic in design, it seems more sensitive to wind than I would have expected (even modest winds). And that gas tank bladder has thrown a couple curves, too, I think (in calculated mileage, which has sometimes been much below, and occasionally way above, the computed mileage).

 

<div class='quotetop'>QUOTE(RonH @ Apr 23 2006, 11:57 AM) [snapback]243988[/snapback]</div>

In sailing that's known as the appearent wind and that's what should be considered when aerodynamics are concerned. The appearent wind is a combination of the true wind velocity and the velocity of the vehicle.

At least we don't have to worry about waves, tide, and current in a car. h34r:

<div class='quotetop'>QUOTE(vtie @ Apr 23 2006, 08:05 AM) [snapback]243926[/snapback]</div>

wtie, I'm curious. What efficiency do you get at 160 km/h in the Volvo?

 

<div class='quotetop'>QUOTE(RonH @ Apr 23 2006, 01:57 PM) [snapback]243988[/snapback]</div>

Hi RonH,

There is more to off-axis winds. The car is designed to minimize form drag from the on-axis wind flow. When the winds come from off center the shape of the car is now different, and not optimized for drag. Additionally, the cross-section area of the car from the squint angle is more. So the aerodynmic drag can go up well beyond what an increase in cross-section area at the apparent wind angle would predict, as the effective Cd can plummet.

This is one of the reasons why large boat-tails are not common on 18 wheeler trucks, at least that was what a friend who did a coop at Cummins told me he had learned there.

What can one do about it? Well, be on the downwind side of the fastest traffic lane, and allot of the effect will be reduced. In the Prius, I have noticed some difference being in the windward, versus the downlind lane on the highway with high off-center head winds. If you can pace a SUV, all the better. Speeding Semi trailer trucks can litterally alow you to drop into dead-band at 70 mph in these conditions! The effect is much more dramatic than in-lane drafting. On the open road I have been pulled up out of the cruise control control range by fast upwind semis, to 80 mph from 70.

I think there may be some aerodynmic devices which will help improve off-axis Cd of the Prius. Maybe in the next generation?

 

I read about a cool system they were considering putting on big trucks. Basically a 4-5 horsepower air-compressor blows a high speed laminar jet of air out of flat shaped nozzles around certain key areas, particularly at the back of the vehicle, so that the turbulent air-flow behind the vehicle ends up way behind the truck and reduces the drag from the reduced pressure at the back. Cut fuel consumption massively, but I've not heard anything about it since.... Clever though.

 

Aww, I'm really sorry that I'm not agreeable to every one of your points.

I think it's very funny you accuse me of being paid! Consider me the counter to these articles. Next time another one of these non objective articles is released or such a post is made, you can count on me to respond (and strongly at that).

"And, MIRZA -- you need to be a bit more objective!!!! Wow, you really seem to see the data that you only want to see. Hey - are you one of those people who are paid to write reviews & opinions in favor of a certain viewpoint or product? Hmmmm - maybe. Well, here's another post for you to reply to and earn a few more cents!"

 

<div class='quotetop'>QUOTE(clett @ Apr 24 2006, 12:01 PM) [snapback]244307[/snapback]</div>

Next up textured, bumpy exteriors.

 

<div class='quotetop'>QUOTE(RonH @ Apr 24 2006, 01:14 PM) [snapback]244317[/snapback]</div>

You mean like golf-balls? Works for them right enough. I suppose smooth isn't always the best way forward - there's a rough coating for airplane wings now that reduces drag. And swimsuits too. They learnt that trick from sharks...

 

<div class='quotetop'>QUOTE(donee @ Apr 24 2006, 11:53 AM) [snapback]244298[/snapback]</div>

Good points. Which is why I wasn't too surprised at the variance reported by the poster I replied to. Sometimes driving to Vegas it feels like I'm going up hill both ways!

Another place you can see this phenomenum is in pro road bike races. A cross wind will spread them out in diagonal lines across the roadway.

<div class='quotetop'>QUOTE(clett @ Apr 24 2006, 12:36 PM) [snapback]244335[/snapback]</div>

and america's cup yachts.

 

As far as VW vs. Prius, I had a rented Golf 2.0 TDI in France that got a solid 48 mpg cruising at up to 150 kph. My Prius gets a solid 48 (sometimes more) with 99% freeway driving. Your mileage may vary...

 

<div class='quotetop'>QUOTE(judibob @ Apr 22 2006, 09:52 AM) [snapback]243620[/snapback]</div>

The C6 is an amazing vehicle. You have to drive one to really be able to appreciate what you get for the money.

 

I happen to own both a 2006 Jetta TDI (manual) and a 2006 Prius. I can't figure out the skepticism here. The article was pretty spot on with the observations about both cars. Granted the Prius was unusually low in the mileage department but they were driving it awfully fast.

I am extremely careful driving the Prius and average 49-53 mpg's depending on driving and weather conditions. However, with the Jetta, which I run on Biodiesel, I average 57 mpg's in highway driving (with some trips above 60) and usually in the 52-54 mpg range with mixed city/highway driving. The main difference between the two cars, as accurately pointed out by Autoweek, is that the Jetta is much easier to drive to get good mileage. The Prius definitely has to be babied to get the really good mileage.

I'm a HUGE Prius fan in every way and think the car is an absolute marvel of technology. But truth be told, a good diesel running on biofuel, can get better mileage and consumes a renewable, non-polluting resource. If only somebody could combine the Prius technolgy with the Jetta diesel efficiency...now that would be the perfect car!

Ron

 

<div class='quotetop'>QUOTE(tripp @ Apr 24 2006, 05:46 PM) [snapback]244259[/snapback]</div>

I don't do this regularly, only on the German autobahn every now and then (driving 100mph there is the safest choice sometimes). Usually, I get somewhere between 7.5 and 8 l/100 km (29 - 32 mpg) when driving at speeds between 160 and 190 km/h. And this is a 4wd car with raized suspesion and light terrain tires. My brother drives a regular Volvo V70 D5 diesel, and he would get between 6.5 and 7.0l/100 km in the same circumstances (33.5 - 36 mpg)

Judging how rapidly the fuel consumption goes up with speed on my prius, there is no way I could get those numbers at these speeds with that car.

 

I also own a 2006 Prius (#4) and a 2002 VW Jetta TDI wagon (manual). Sorry folks, but the Jetta is clearly winning the mpg battle for us. Both vehicles are used mostly for highway driving. The new prius has yet to get over 43 mpg even in warmer weather. The used TDI was getting 43 mpg in the winter on blended fuel. The two recent tanks have been 48.5 and 45 mpg.

Maybe the Prius mileage will improve once the vehicle is broken in. We do like the Prius overall; however, the Jetta is more fun to drive, has much more comfortable seats, and a much better sound system. The prius clearly wins the back seat room battle though.

A hybrid diesel would be awesome.

 

One other aspect one should not forget in this whole prius/diesel debate is that the main goal of the prius was not to minimize fuel consumption. It was to maximise the environment-friendlyness of the car.

In this respect, a diesel still has a few important disadvantages: NOx emissions, particle emissions, and even CO2 emissions. The Prius CO2 emission is rated at 104g/km, whereas the Jetta TDi is still at 136g/km.

There is no doubt that the Prius is a much cleaner vehicle than the Jetta TDi. It also uses less natural resources, if you take into account the fact that you need 15% more fossile oil to come to the same amount of diesel as for gasoline. And don't start talking about the joke of bio-diesel... Right now, producing it is *not* environment-friendly nor efficient on natural resources at all. It definetely has future promise, but fot the moment it is mainly the result of efficient lobbying of the agricultural industry.