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

[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!

[GasSavers_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]

Originally Posted by Jack

showed them the graph. He finally got it then.

worth 1000 words, isn't it! :P

[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.

[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.

[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.

[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.