mpg vs. speed

[MetroMPG]

See: http://www.metrompg.com/posts/speed-vs-mpg.htm

km/h - W mpg - E mpg
55 ... 83.1 ... 82.4
60 ... 77.8 ... 76.3
65 ... 74.1 ... 71.7
70 ... 71.2 ... 70.8
75 ... 67.2 ... 62.7
80 ... 63.3 ... 59.3
85 ... 59.4 ... 56.4
90 ... 55.4 ... 53.9
95 ... 51.5 ... 50.3
100 ... 46.6 ... 46.9
105 ... 44.9 ... 44.0

[Matt Timion]

Looks like someone is going to be cruising at 55 km/h for a while :P

[MetroMPG]

i could drive my '89 accord all day at 95 km/h on cruise control and beat its hwy rating by 20-30%.

[MetroMPG]

Originally Posted by Matt Timion

Looks like someone is going to be cruising at 55 km/h for a while :P

you'd think so, eh?

but actually, nope - i really don't like the way the engine sounds & feels down there. my lowest comfortable cruising speed in 5th is 65 km/h.

i only tested the lower speeds because jan asked about it a while ago.

[Matt Timion]

Originally Posted by MetroMPG

one thing this confirms to me is that the blackfly's highway EPA rating is harder to beat compared to other cars i've driven. meaning, the constant speed at which the blackfly attains its EPA rating is slower than other cars.

i could drive my '89 accord all day at 95 km/h on cruise control and beat its hwy rating by 20-30%.

same thing with my mom's car. i borrowed it (1997 camry 2.2 automatic) and ran the same road after doing the blackfly today. its EPA highway speed (30 mpg US) ... 112 km/h / 75 mph! that's nuts.

I actually remember reading that the EPA estimates are obtained at 60mph for highway speeds.

I think the Geos are more difficult to beat becasue they have smaller engines are are more efficient by default. As we know, it's hard to squeeze blood from a highly fuel efficient turnip..

Wait, wrong analogy.

[MetroMPG]

Originally Posted by Matt Timion

As we know, it's hard to squeeze blood from a highly fuel efficient turnip..

yes! exactly what i was going to say

but surely the prius is one of the most efficient turnips out there. yet its graph shows its EPA highway rating (51 mpg) is achieved at around 68 mph - 8 mph higher than the the fireflea's EPA hwy speed.

too bad we don't know what conditions that prius graph was made under for comparison - the site i found it on didn't have any context either.

if any other scangauge equipped people are reading this, do you know what speed gives you your EPA highway rating?

[JanGeo]

First let me say WOW! I didn't expect the slope to be that negative and would have expected a little peak somewhere where system overhead would have been greater than drag for low speeds.

I don't have a level enough road around this area of the country to do testing at various speeds but will give it a try at some point. Maybe if I can find a test loop somewhere - where is a test track when you need one huh! Would love to just drive in a circle on a level track for a few minutes and get some numbers.

[krousdb]

Originally Posted by Matt Timion

I actually remember reading that the EPA estimates are obtained at 60mph for highway speeds.

The highway test loop is done at various speeds where 60MPH is the max and the average speed is 48MPH IIRC. There is more info at fueleconomy.gov but I am too lazy to look it up. Then beginning in 1985 the highway numbers were slashed by 22% and the city numbers were cut by 10% to reflect more real world driving conditions. The 1984 CRX 1.3L was rated 67 MPG highway. The 1985 CRX HF was rated at 54 MPG, about 22% lower.

Now for the next model year they will be slashing the numbers even further to reflect real world driving conditions. Driving conditions in my world are obviously not "real world" conditions.

[krousdb]

Originally Posted by MetroMPG

yes! exactly what i was going to say

but surely the prius is one of the most efficient turnips out there. yet its graph shows its EPA highway rating (51 mpg) is achieved at around 68 mph - 8 mph higher than the the fireflea's EPA hwy speed.

too bad we don't know what conditions that prius graph was made under for comparison - the site i found it on didn't have any context either.

if any other scangauge equipped people are reading this, do you know what speed gives you your EPA highway rating?

I was actually thinking about the same thing recently, only I was thinking how much easier it is to exceed EPA in the Del Sol than it is in the Prius. In the Del Sol, I can achieve ~80% over combined EPA on my daily RT commute. In the Prius, I can only get 50% over.

I suspect that since the automakers have knowledge of what the test routine is for EPA, that perhaps they "tune" the engine and transmission of the high FE models to produce the best EPA results, which helps to sell the high FE models. On the run of the mill FE models and sporty models they tune for driver satisfaction, which is what helps sell the non FE models.

I dunno. Just a theory of mine.

[philmcneal]

what we need is good power to weight + areodynamics ratio, and the EPA tests never take areodynamics and weight as a factor. Just the engine, as you can see even using it as a "comparason" factor seems kind of out of place due to the differences in cars.

[MetroMPG]

Originally Posted by krousdb

I suspect that since the automakers have knowledge of what the test routine is for EPA, that perhaps they "tune" the engine and transmission of the high FE models to produce the best EPA results, which helps to sell the high FE models.

sounds like a good theory to me. my last 3 tanks would have me at 29% above combined epa.

let's have a look at basjoos' numbers: he's about 20% above EPA @ lifetime mpg. if you just look at his 3 most recent tanks, roughly 62-ish, he's about 38% above.

and fredvx: 27% over EPA (2 tanks).

nothing outright conclusive, but it's good supporting evidence for your theory about epa & "efficient" cars.

[MetroMPG]

Originally Posted by philmcneal

EPA .... using it as a "comparason" factor seems kind of out of place due to the differences in cars.

maybe, as the EPA sometimes says, never mind absolute accuracy, it's a valid way to compare cars in the same class. (i'm pretty sure i've read that 'defense' of the ratings before.)

e.g. it's valid to compare a metro vs a vx, or a regular civic against a regular corolla, but not the vx against the corolla.

[philmcneal]

i was more concerned over the areodynamics since that wasn't a factor for the old epa testing.

[95metro]

Thanks for that chart metroMPG! Totally explains why my fuel average went UP after I STOPPED highway driving. With our 110 km/h speed limits in Alberta (and having to hit 115 to keep from getting run over) that totally explains why I could barely hit a 40 mpg average. I must have been get about 35 mpg on the highway during the winter! Yuck!

PS: I've heard that the Sprint/Firefly Turbos get WAY better highway mileage than the NA clones. Wouldn't mind testing a turbo setup with 1 or 2 pounds of boost for the city and then adjusting it to the stock 7 pounds for highway.

[MetroMPG]

you're welcome. now that your at gassavers, you get an early look at stuff i eventually clean up and post at metrompg.com

i can get away with 95 km/h on the freeway unless i'm getting closer to ottawa or toronto, so i haven't taken as much of a highway hit as you have.

i hadn't heard that the turbos got better mileage. that's very interesting...

[MetroMPG]

FYI - for those who were interested in this thread, I've (finally) posted a summary, with some new cleaned up images, at MetroMPG.com:

• Speed kills: testing MPH vs. MPG in top gear

[SVOboy]

New transmission graaaaaph!

[Jack]

Thanks for the info and the link to the Graph. I was trying to explain that to someone today at lunch for 20 minutes. Got back and showed them the graph. He finally got it then.

[MetroMPG]

If I did a new one today with the new transmission, you couldn't compare it directly to the original, since it was made when the temps were 58 F.

In fact, I realized last night that my claim of 8.x% improvement with the taller transmission is faulty, because I based it on the colder ambient speed/mpg data. The actual transmission improvement is less.

[MetroMPG]

Originally Posted by Jack

showed them the graph. He finally got it then.

worth 1000 words, isn't it! :P

[thisisntjared]

i think its interesting that they took the time to show that when you go too slow in the top gear of some cars you lose efficiency. in the '86 gti it clearly shows that your peak efficiency is 40mph but any slower is less efficient. as also sited from fueleconomy.gov, there is an efficiency that peaks around 45-50mph in the top gear. even though their source seems somewhat arbitrary...

now i have heard contrary info from some of you guys.... logic tells me that when the rpms go too low some motors, particularly hondas become inefficient.

[SVOboy]

I think you've seen my graph. It's better the slower you go, though not by much. However, in normal driving where you can't just cruise completely unimpeded 30mph at 1k rpms is not as good as mehbe a bit higher because of the little changes you have to make. However, it's still better than being in 4th gear so there's not much to do about it.

[MetroMPG]

Originally Posted by thisisntjared

i think its interesting that they took the time to show that when you go too slow in the top gear of some cars you lose efficiency. in the '86 gti it clearly shows that your peak efficiency is 40mph but any slower is less efficient.

But... look closer at the GTI graph. The efficiency drop below 40 mph is in 4th gear, not 5th. So its peak efficiency is the lowest tested speed in 5th gear:



Also, the EPA graph doesn't say whether it's all in top gear or not, but I doubt it is - it's too similar to the shape of the GTI graph to be coincidental.

I suspect the peak of the EPA graph is for a car with an automatic transmission, which shifts into overdrive around 50 mph. Conjecture. I've yet to see a graph that shows better fuel efficiency at except in top gear at the lowest possible speed.

[MetroMPG]

Originally Posted by SVOboy

I think you've seen my graph. It's better the slower you go, though not by much.

Actually I forgot about it, but yeah, that's a crazy graph (Speed versus MPG (CRX))

If it's OK with you, I might fix it up a bit and post it on my site with the others. But I want more methodology info: what were the temps, and were the readings averages of bi-directional runs, or one-way? All repeated on the same stretch of road? Other cars around? (I cancel runs where I'm in another car's wake - I don't mean drafting).

(Feel free to reply in your graph thread.)

[thisisntjared]

Originally Posted by MetroMPG

But... look closer at the GTI graph. The efficiency drop below 40 mph is in 4th gear, not 5th. So its peak efficiency is the lowest tested speed in 5th gear:



Also, the EPA graph doesn't say whether it's all in top gear or not, but I doubt it is - it's too similar to the shape of the GTI graph to be coincidental.

I suspect the peak of the EPA graph is for a car with an automatic transmission, which shifts into overdrive around 50 mph. Conjecture. I've yet to see a graph that shows better fuel efficiency at except in top gear at the lowest possible speed.

very good point! i totally didnt notice, however look at the changes in 2nd gear and the changes in 4th gear. there is something to be said for that...

[MetroMPG]

Originally Posted by thisisntjared

look at the changes in 2nd gear and the changes in 4th gear.

Good eye! Hadn't thought about that and can't explain it either. I was really just looking at the 5th gear stuff, since that's what I did in my car.

I wonder if I did a range of constant speed runs in all my gears whether the best mpg for each gear would always be at the lowest practical speed the gear could be driven. My first instinct is "yes", but I'm not certain now.

I could see first gear from 0 mph perhaps showing an oddball result, but I'm surprised 4th is different from 5th.

[SVOboy]

We could always hook my MID up to jared's car and test it out for ourselves,

[MetroMPG]

Don't let me stop you. Go get some data! I'll may go around the block a couple of times later in the Flea just to see what the SG says about it.

[SVOboy]

Well, that's all up to jared. I figure he's busy with marriage or something, I'll just send it to him before I leave for school or something, if he wants, that is.

[thisisntjared]

Originally Posted by SVOboy

We could always hook my MID up to jared's car and test it out for ourselves,

i have a feeling itll be good at lower speeds just because of my awesome 4.25 final drive and .702 5th