Consumer Reports tests speed vs MPG & comes to false conclusion about Honda Insight 2

[tjts1]

The comments on the autoblog article are surprisingly intelligent. Seem like most people have a concept of gallons per mile much more so than the editor.

[bwilson4web]

Thanks to friends, I've finally gotten some Jetta (maybe Golf) TDI, mph vs MPG data and updated this graph:

I'll attach my spreadsheet so folks will have the data but here is how I see it.

MPG at 75 mph is the key data point. Cars that get better than 40 MPG at 75 mph will do well in the EPA, Euro and automotive press. But if their highway mileage is under 40 MPG, they will be reported as 'dogs.' Notice that my NHW11 fits in that category but the reason for my lifetime 52+ MPG is extensive used of 65 mph as my highway speed limit. But the EPA thinks it is a 41 MPG highway car. Knowing where the 'knee in the curve is,' allows an informed driver to trade off: good, fast and cheap.

Bob Wilson

[some_other_dave]

Originally Posted by bwilson4web

You'll notice that:

70 mph -> 25 hp
75 mph -> 30 hp

That is still a low throttle setting to my way of thinking. I really don't think I understand what you are saying...

-soD

[bwilson4web]

Originally Posted by some_other_dave

That is still a low throttle setting to my way of thinking. I really don't think I understand what you are saying...

What happens is the 25-30 hp point is on a steep part of the power required curve. Any slight rise or additional drag requires the engine to run up that curve into higher consumption and even more inefficient power settings:


The areas of peak engine efficiency are marked by the small, red dots. You'll notice the 25-30 hp curve fall right under the last of them. Any higher power demands push the engine into inefficient, lower BSFC regions.

So it is a combination of two effects:

• steep power slope - so any local variance in power demand will rapidly go into much higher power regions
• upper limit of high efficiency - anything over 30 hp is going to have lower BSFC than the 25-30 hp region.

I've thought about making a cruise control device that limits the peak HP setting, just using the ICE rpm of say 2,600 rpm AND a maximum speed. The car would slow down going up a hill but it would stay in a fuel efficient mode. But it in an actual design, I would allow excursions up to 3,400 rpm to handle hills. If any more is needed, the accelerator would be used.

Bob Wilson

[MetroMPG]

This time at cars.com:

At Highway Speeds, Mileage Drops More for Fuel-Efficient Models - link to article
As with the AutoBlog piece, a few commenters immediately point out the flaw in the analysis. And then they're countered by people who insist on things like:

I've found just the opposite on my 95 Neon. During my latest trip ... I went between 75-80 the entire way and got on average 42mpg. Whereas going slower I generally only get between 35-37mpg.

...and...

I also get better mpg the faster I drive. I used to have a 91 Civic 5-spd and I always got the best mileage out of it if I drove above 80 mph. I'm beginning to notice the same with my 04 Mazda3.

Sheesh.

[Luxbg]

Originally Posted by MetroMPG

This time at cars.com:

At Highway Speeds, Mileage Drops More for Fuel-Efficient Models - link to article
As with the AutoBlog piece, a few commenters immediately point out the flaw in the analysis. And then they're countered by people who insist on things like:

...and...

Sheesh.

It is quite funny, but I had a similar experience. Before I got my Lancer I used to drive a Neon and averaged about 200 miles per tank (back then I didn't use to pay too much attention to milage so this is as exact as I can get). One summer however I undertook a road trip to Canada and was in a bit of a rush getting home where I did 80 - 85 mph the whole way home with very few brakes on the 800 mile trip. Surprisingly, I got almost 280 miles out of my last tank on that trip. Considering how fast I was going this surprised me back then, compared to my usual highway speed of 65.

In retrospect I realize that there were a few favorable factors that helped with the big mileage jump: first it was exclusively highway driving, my regular tanks always included about 30-40% city driving and as I now know, without proper driving technique city really kills gas mileage. Second, for about 3/4 of the tank I was following a Jeep Wrangler that seemed to be in as much a hurry as me. I was following behind at a reasonable difference but at that speed, even that probably had an impact on my mileage. Lastly, going from Pittsburgh to Baltimore has a net negative elevation change of more than 1000 feet so that probably wasn't detrimental to my mileage either.

I guess what I'm trying to say is that a lot of people who are not very informed on the subject, may pull generalizations from similar personal experiences, not realizing that they're missing vital parts of the puzzle.

[MadisonMPG]

The comments on Consumer Report are getting worse and worse.

[bwilson4web]

I posted a pointer to this chart at the Consumer Reports comments:


Personally, if this has 'struck a chord' with various vehicle advocates, it will be a good thing. Maybe they'll get busy and start measuring actual vehicle performance.

Bob Wilson

[gone-ot]

paraphrasing a VERY old quotation: "...you can lead an idjiot to data, but you can't make him/her believe it."

...perceptions are an 'individuals' information filters...they only let 'in' what that individual wants to hear or see.

[Jammer]

Gang:

We just can not trust Consumer reports as a sole source to base our car purchases on. I have read their mag off and on through the years and I don't think I even once agreed with them on products that I knew something about. It's a cool idea to have a service that does not supposed to except advertising, but that just opens the doors to kick-backs, just like we have in politics. I am NOT accusing Consumer reports of such practices, but I often scratch my head in wonder as to why and how they conclude their winners from their losers. Sometimes things are good because they are heavy and sturdy, then something is good because it is lightweight and flexible.... I just want to scream when I read their review of products that I already know the details of. I can not think of a single time I agreed with them.