Mpg vs. Outside temp

mac.mogul · Mar 24, 2014

Lets apply that to real life.

If you're at sea-level and it's 30 degrees F outside, the difference in drag from 30 degrees and 80 degrees is negligible and has little to no effect on your car's performance.

We're not driving cars at 450mph at 35,000 feet when it's 60 degrees below 0F.

There's a good chance that driving a dirty car will affect drag more than temperature difference will.

bshin352 · Mar 24, 2014

Are there wind tunnel pics of the focus?

Tigeo · Mar 24, 2014

Here is some good info that most have covered here..but hey...this is from the governemnet so you knows its true [clap]

http://www.fueleconomy.gov/feg/coldweather.shtml

bshin352 · Mar 24, 2014

Tigeo said:
Here is some good info that most have covered here..but hey...this is from the governemnet so you knows its true [clap]

http://www.fueleconomy.gov/feg/coldweather.shtml

I never thought I'd see good info, government and true in the same sentence.

Is this real life?

goingtoscotland · Mar 24, 2014

mac.mogul said:
Lets apply that to real life.

If you're at sea-level and it's 30 degrees F outside, the difference in drag from 30 degrees and 80 degrees is negligible and has little to no effect on your car's performance.

We're not driving cars at 450mph at 35,000 feet when it's 60 degrees below 0F.

There's a good chance that driving a dirty car will affect drag more than temperature difference will.

it is definitely not a negligible difference

mac.mogul · Mar 24, 2014

Enough drag to destroy your fuel mileage? Hardly.

goingtoscotland · Mar 24, 2014

Enough to affect it by a couple mpg at least depending on speed. When coupled with the rest of factors it really doesn't help.

Drag increases exponentially the faster you go, which means you need an exponential increase in power to overcome that drag. The same goes for an increase in drag due to air density. I can't say exactly how much power is needed to maintain 70mph in a Focus on a standard day at sea level on level ground, because I don't know the coefficient of drag for the Focus. If you add 12-15% or more to the amount of drag encountered it's going to make a sizable dent in your mpgs.

BetaDnB · Mar 24, 2014

goingtoscotland said:
I don't know the coefficient of drag for the Focus.

The sedan is .297. [grinking]

jsr72 · Mar 25, 2014

goingtoscotland said:
Enough to affect it by a couple mpg at least depending on speed. When coupled with the rest of factors it really doesn't help.

A back-of-the-envelope calculation gives a rough estimate of a 1 mpg change per 30 deg F at 70mph due to air density effects.

thenorm · Mar 25, 2014

goingtoscotland said:
Enough to affect it by a couple mpg at least depending on speed. When coupled with the rest of factors it really doesn't help.

If you add 12-15% or more to the amount of drag encountered it's going to make a sizable dent in your mpgs.

rule of thumb is that a 2% change in aero drag at hwy speed has a 1% change in MPG

thenorm · Mar 25, 2014

jsr72 said:
A back-of-the-envelope calculation gives a rough estimate of a 1 mpg change per 30 deg F at 70mph due to air density effects.

i get the exact same number.
air density changes by about 5% every 30F. therefore aero drag changes by 5%.
by my rule of thumb that gets 2.5% change in MPG on the hwy. which is 1mpg on a 40mpg hwy car.

Mpg vs. Outside temp

mac.mogul

bshin352

Tigeo

bshin352

goingtoscotland

mac.mogul

goingtoscotland

BetaDnB

jsr72

thenorm

thenorm

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