Topic: Popular Mechanics tests 40mpg fuel economy claims, with sexy results!

[Sir Osis of Liver]

Well, ok, not sexy, but interesting for mileage geeks.



http://www.popularmechanics.com/cars/news/fuel-economy/mileage-moment-of-truth-we-put-40-mpg-claims-to-the-test-6651300

Pretty big difference in the 70mph results. Certainly looks like the Elantra has an edge in the drag coefficient or frontal area.

[mmret]

Interesting. Looks like

1. EPA numbers are pretty realistic/pessimistic.

2. Despite the dead heat between the two cars in the City and 55MPH tests, the Elantra is way better in the 70MPH test. Is the Focus somehow much less aerodynamic? Is the gearing too short? With a sizeable torque advantage you'd think the Focus could handle high speed low RPM cruising better than the Elantra but apparently not. I'm guessing its not the weight since that didn't seem to hold the Focus back in the other two tests, and at a constant cruise the only relevant energy loss relation to weight is rolling resistance, which if I am not mistaken is dwarfed by the weight-irrelevant aerodynamics.

[Sir Osis of Liver]

Interesting. Looks like

1. EPA numbers are pretty realistic/pessimistic.

2. Despite the dead heat between the two cars in the City and 55MPH tests, the Elantra is way better in the 70MPH test. Is the Focus somehow much less aerodynamic? Is the gearing too short? With a sizeable torque advantage you'd think the Focus could handle high speed low RPM cruising better than the Elantra but apparently not. I'm guessing its not the weight since that didn't seem to hold the Focus back in the other two tests, and at a constant cruise the only relevant energy loss relation to weight is rolling resistance, which if I am not mistaken is dwarfed by the weight-irrelevant aerodynamics.

Yeah. I'm not sure of the answer. Could be a combination of a shorter 6th gear and worse aero characteristics.

[johngenx]

Lots of variables influence highway fuel economy, including gearing (can be too tall too, causing large throttle openings or lots of downshifts), aero qualities, engine management, tires, etc.

Our Corolla has a pretty short fourth (top) gear, but still sees outstanding highway fuel economy. Driving at 110km/h, it's revving fairly high, but has a very small throttle opening to maintain speed and very good engine management (variable valve timing, fuel management, etc) along with a very slippery shape.

Another John might be along any moment to explain that tall gearing is the be all and end all regardless of engine size and power curves, but it is only one factor in what fuel economy a car achieves.  When I first bought my old 1979 Camaro, the final drive was so tall the car ticked over at 1200 rpm at over 100km/h, and yet the old body conspired with the ancient technology 5.7L engine to reward me with dismal fuel economy.

Without some serious engineering investigation, it would be impossible to isolate one variable that accounts for the poorer highway fuel economy of the Ford, and even with mountains of data, one variable might not be the sole reason.

[Jaeger]

That is a huge difference at what is a fairly common highway cruising speed.

Surprising.

Jaeger

[SaskSpecV]

Nice find SirO.  I too am thoroughly surprised that the Focus economy dropped that much at 70 mph.  That's only ~ 110 kph, not real fast by today's standards.  And I thought the "SFE" package had all kinds of active shutters and grilles and whatnot to reduce drag at higher speeds?  Just not effective or what?

[Keh-vin]

The answer to the Focus questions is quite simple really, it goes like this: "Nah...Ford's just suck."  Anything over 55-60 mph and it's like you've opened up the taps to Niagra Falls.  I know, I have 2 (Fords).  F150 at 95-100 kmh, 11-12ish l/100; Fusion around 8l/100.  Go for 110, even 120, and  15-18 for the truck (wind dependent) and 11-12 for the car.  They rev too high.  Everyone else revs at what, 1800 at 110-120?  Mine, 2100+.  So there's your answer.  (See sig - my averages are awful)

[Seafoam]

Lots of variables influence highway fuel economy, including gearing (can be too tall too, causing large throttle openings or lots of downshifts), aero qualities, engine management, tires, etc.

Our Corolla has a pretty short fourth (top) gear, but still sees outstanding highway fuel economy. Driving at 110km/h, it's revving fairly high, but has a very small throttle opening to maintain speed and very good engine management (variable valve timing, fuel management, etc) along with a very slippery shape.

Another John might be along any moment to explain that tall gearing is the be all and end all regardless of engine size and power curves, but it is only one factor in what fuel economy a car achieves.  When I first bought my old 1979 Camaro, the final drive was so tall the car ticked over at 1200 rpm at over 100km/h, and yet the old body conspired with the ancient technology 5.7L engine to reward me with dismal fuel economy.

Without some serious engineering investigation, it would be impossible to isolate one variable that accounts for the poorer highway fuel economy of the Ford, and even with mountains of data, one variable might not be the sole reason.

It's too bad they didn't test more cars such as your corolla and the civic in that class. I bet that even with a worse rating than the elantra and focus,they would be very close.Maybe autos.ca will do challenge like they did a few years ago.
I'm not sold yet on the direct injection that many of these cars possess. I'd wait for 5 years to see if the engines are not full of carbon deposits. 

[johngenx]

I'm not sold yet on the direct injection..

Me neither.  The lack of cleaning for the valvetrain is a real concern.  As I've noted elsewhere, I think Toyota has the best system currently, using both port and direct injection to maximize the benefits of both.  However, it's currently more expensive to install.

The "old think" Corolla (no DI, four speed AT) rewards owners with outstanding fuel economy.  I think the main reason is aerodynamic engineering combined with an engine management system that uses the variable valve timing to minimize consumption.  They seem to have chosen the AT ratios to keep the car is a "sweet spot" at about 100km/h or so, using a very small throttle opening but is deep enough into the torque band to keep the car from downshifting or needing much additional throttle for small grades.

If only the engineers at Toyota that work on fuel economy could find some "exciting" friends that infuse more passion into the products.  Perhaps their new partnership with Subaru and the 86/BRZ is pointing to the future?  Here's hoping...

[mmret]

The answer to the Focus questions is quite simple really, it goes like this: "Nah...Ford's just suck."  Anything over 55-60 mph and it's like you've opened up the taps to Niagra Falls.  I know, I have 2 (Fords).  F150 at 95-100 kmh, 11-12ish l/100; Fusion around 8l/100.  Go for 110, even 120, and  15-18 for the truck (wind dependent) and 11-12 for the car.  They rev too high.  Everyone else revs at what, 1800 at 110-120?  Mine, 2100+.  So there's your answer.  (See sig - my averages are awful)

My TSX revs 2400 at 120. And gets mid 7s. Answer mustbe more complex.

[Sir Osis of Liver]

The bike revs at 5k at 100km/hr, still get 5L/100km.

[rrocket]

The bike revs at 5k at 100km/hr, still get 5L/100km.

Really?  What a buzzbomb! 

[Gamefreak]

Wish my Elantra did 2100rpm at 120, or even 2400...

[Sir Osis of Liver]

The bike revs at 5k at 100km/hr, still get 5L/100km.

Really?  What a buzzbomb! 

Yup 14.5k redline.

[rrocket]

The bike revs at 5k at 100km/hr, still get 5L/100km.

Really?  What a buzzbomb! 

Yup 14.5k redline.

That's it? 

[Sir Osis of Liver]

The bike revs at 5k at 100km/hr, still get 5L/100km.

Really?  What a buzzbomb! 

Yup 14.5k redline.

That's it? 

I'm not exactly running at Donnington.

[quadzilla]

I wonder if they drove the cars at the same time so weather wasn't a factor?

Most of my driving is highway and I usually check to see what kind of mileage I get. I drove to the same location in Hamilton (from Toronto) twice with different conditions.

Run #1
Speed between 100-110kph, tame driving, very strong head winds = 8.7L/100

Run #2
Speed between 120-140kph, always on the throttle, tail winds = 7.4 L/100

With so many variables in play, I never take any of these test as the final answer.

I do like their formula though.

[Juke1]

I would love to test drive a bunch of small cars, let's say a week at a time, but my way.  That's usually left lane driving   That would produce "real life testing" results.

[SaskSpecV]

With so many variables in play, I never take any of these test as the final answer.

I do like their formula though.

That's why the 50L-challenge was so awesome.  Multiple compacts driving down the same road, at the same time, at the same speed.  No other variables.  Cruising like a herd of turtles...  When are we going to see a new one?

Of course, just because vehicle X got better milage than vehicle Y at Z km/h, doesn't mean a graph of delta XY versus different values of Z will have a slope of 0...  Sorry, I was getting into that Pop Mech formula too!

[Jaeger]

I wonder if they drove the cars at the same time so weather wasn't a factor?

That was my impression from reading the article.

Jaeger