Interesting MPG experiment

[Sheldon]

I have installed a trip computer on my 2001 Forester 2.5 AT.
See measured gas mileage driving highway with constant speed for at
least 15 miles:
MPH MPG
37 39
50 34
62 28
68 26
81 21

Nice test. Sounds like we're talking drag here. So, what about a car like
a Ferrari that isn't shaped like a shoebox? Would the best mileage be at
"relatively" higher speeds? And yes, I do realize nobody buys a Ferrari to
save money on gas.

 

[Clifford Heath]

Nice test.
Agree.

Sounds like we're talking drag here. So, what about a car like
a Ferrari that isn't shaped like a shoebox? Would the best mileage be at
"relatively" higher speeds? And yes, I do realize nobody buys a Ferrari to
save money on gas.

Actually, aerodynamics isn't a visual art. IOW, some remarkably
unappealing lines can have quite low drag. For example, the Giulia
Super is boxy, yet has a CD around 0.3 - much lower than you'd
expect from looking at it. They reckon it has a lot to do with
small details like the fillet at the base of the windscreen, etc.
So don't assume that the shoebox is necessarily all that bad.

The CD gets multiplied by the frontal area - go bigger/higher, you
get more drag for the same CD... obviously.

 

[clare at snyder dot ontario dot canada]

Actually, aerodynamics isn't a visual art. IOW, some remarkably
unappealing lines can have quite low drag. For example, the Giulia
Super is boxy, yet has a CD around 0.3 - much lower than you'd
expect from looking at it. They reckon it has a lot to do with
small details like the fillet at the base of the windscreen, etc.
So don't assume that the shoebox is necessarily all that bad.

The CD gets multiplied by the frontal area - go bigger/higher, you
get more drag for the same CD... obviously.

OK - just back from 17 day road trip with 2.4 liter PT Cruiser - 4
adulta and luggage (approx 1000 lbs total load)
6231km. 626.23 liters total. Average fuel economy 29MPG (imperial)
Best tank 34MPG - on 2 tanks. 29, 29.5 and 30 on 3 other tanks. 28 on
5 tanks, 25 and 26 on 5 more.
Interestingly, the 28mpg tanks were the lowest speed steady driving
sections of the trip - running 100kph +/- 10 on generally level to
gently rolling roads. The 25 and 26 mpg tanks were in slow driving
areas, generally with fair to severe hills. The 34MPG tanks were on
high speed sections - long runs of 117 - 123 KPH including some very
hilly country (like between Calais Maine and Stowe Vermont and between
Hartland and Shediac New Brunswick), and the 29-30mpg sections were
in the hills with manual downshifting .

ALL of the high MPG runs were with the engine running over 2800RPM -
some significantly so (4000 RPM up hills at half throttle or less)
while the low mileage sections were generally under 2500 RPM - only
downshifting when fairly heavy throttle caused the engine to downshift
- otherwize "lugging along) at 2200-2400 RPM.
Interestingly, if I manually downshifted going up a hill with my foot
into it but not hard enough to automatically downshift, barely
maintaining speed, I had to get my foot WAY out of it to avoid gaining
significant speed, even on 6-10% grades. At 3400 RPM in third the
throttle was almost closed, compared to almost wide open at 2600 in
overdrive.
This is the way I drove in the hilly areas where I got the best
mileage.
Anything under 2800 RPM, or better yet 3000+, power output (torque) is
so low the engine is lugging and hard on fuel. The increase in engine
efficiency at higher speeds more than made up for the extra drag from
speed on the less than perfect, arodynamically, PT Cruiser.

The best mileage I have gotten on this car previously, driving at a
steady 100kph (62MPH) on the VERY level drive between Waterloo and
Windsor Ontario on the 401 was 28mpg (with 4 adults). Paying a little
less attention to smooth starts, and passing a few cars, between
Waterloo and Barrie ontario, I got 26 (alone in the car, with no
load). Around town I get 24 (roughly 50/50 town streets and
"expressway", but trips of 15K or less each)

I suspect with 1/4 the load I could acheive in the neighbourhood of
42MPG with this car at 117-120KPH on a trip- and it is not nearly as
aerodynamic as the 1975 Celica GT. Narrower 15 inch tires instead of
the low profile "fatties" supplied from the factory would add another
couple MPG at 40PSI.

 

[JD]

in message

OK - just back from 17 day road trip with 2.4 liter PT Cruiser - 4
adulta and luggage (approx 1000 lbs total load)
6231km. 626.23 liters total. Average fuel economy 29MPG (imperial)
Best tank 34MPG - on 2 tanks. 29, 29.5 and 30 on 3 other tanks. 28 on
5 tanks, 25 and 26 on 5 more.
Interestingly, the 28mpg tanks were the lowest speed steady driving
sections of the trip - running 100kph +/- 10 on generally level to
gently rolling roads. The 25 and 26 mpg tanks were in slow driving
areas, generally with fair to severe hills. The 34MPG tanks were on
high speed sections - long runs of 117 - 123 KPH including some very
hilly country (like between Calais Maine and Stowe Vermont and between
Hartland and Shediac New Brunswick), and the 29-30mpg sections were
in the hills with manual downshifting .

I got that good with an STi on a round trip from Halifax to Toronto and back
driving at 110-115 (2800-3000 RPM)

ALL of the high MPG runs were with the engine running over 2800RPM -
some significantly so (4000 RPM up hills at half throttle or less)
while the low mileage sections were generally under 2500 RPM - only
downshifting when fairly heavy throttle caused the engine to downshift
- otherwize "lugging along) at 2200-2400 RPM.
Interestingly, if I manually downshifted going up a hill with my foot
into it but not hard enough to automatically downshift, barely
maintaining speed, I had to get my foot WAY out of it to avoid gaining
significant speed, even on 6-10% grades. At 3400 RPM in third the
throttle was almost closed, compared to almost wide open at 2600 in
overdrive.
This is the way I drove in the hilly areas where I got the best
mileage.
Anything under 2800 RPM, or better yet 3000+, power output (torque) is
so low the engine is lugging and hard on fuel. The increase in engine
efficiency at higher speeds more than made up for the extra drag from
speed on the less than perfect, arodynamically, PT Cruiser.

That's really weird. I get in the 8.8/100 (34 MPG) with the Forester at 90
KPH. It drops to 10/100 (30 MPG) at 110.

The best mileage I have gotten on this car previously, driving at a
steady 100kph (62MPH) on the VERY level drive between Waterloo and
Windsor Ontario on the 401 was 28mpg (with 4 adults). Paying a little
less attention to smooth starts, and passing a few cars, between
Waterloo and Barrie ontario, I got 26 (alone in the car, with no
load). Around town I get 24 (roughly 50/50 town streets and
"expressway", but trips of 15K or less each)

I suspect with 1/4 the load I could acheive in the neighbourhood of
42MPG with this car at 117-120KPH on a trip- and it is not nearly as
aerodynamic as the 1975 Celica GT. Narrower 15 inch tires instead of
the low profile "fatties" supplied from the factory would add another
couple MPG at 40PSI.

I seriously doubt you could. The best I can get with the Forester (2.5L) is
around 2000 RPM (75 KPH) at around 8.2/100 (36 MPG) on flat ground. Did it
on the prairies for nearly 400 km.

 

[AlFire]

I seriously doubt you could. The best I can get with the Forester
(2.5L) is around 2000 RPM (75 KPH) at around 8.2/100 (36 MPG) on flat
ground. Did it on the prairies for nearly 400 km.

FWIW: I have recently drove from Chicago to Phoenix - 1800 miles - and
my MPG was varying from 19 closet to Chicago to 21 in NM and AZ. And I
was ridding very steady 55MPH on cruise control and towing medium U Haul
trailer loaded really well by MB E320T 4Matic also packed up to the roof.

I do know if that 2MPG difference is coming from the different gas
(ethanol?) which or the altitude.


Here is a nice tool http://www.tdiclub.com/misc/conversions.html:

19 MPG = 12.3 l/100km = 22.9 impMPG

21 MPG = 11.2 l/100km = 25 impMPG

Andy

 

[k thoggee]

Hi,

Yeah, of course they are! Learn to drive and I'll bet you find yourself
in far fewer of these "situations." People "root for crashes" at NASCAR
races... on the road, it ain't no race.

I know how to drive. I've been doing it in nasty Canadian weather for 20
years.

But anyway that's not the point: why are they rooting for crashes to begin
with? Why do they try to foment them? And why don't you consider that to be
attempted homicide? Are you telling me you're *for* someone who tries to
kill, but only sometimes?

God forbid you ever drive a car, as I do, that "looks fast" with the
hoodscoop and the tailfin. Then they'll be doing it to you too.

Maybe someday you'll understand, as I do, that the only way to *escape* the
oppression of the other drivers on the road is to drive a car that is so
crushingly powerful, so well-tuned, so agile, that it is no longer possible
for them to try to kill you with *nearly* so high a probability of success.
You can finally escape their bullying, antisocial behaviour.

Until then, tail lights wave bye-bye.

I see quite a few "wannabe racers" (sadly for the marque, more than a
few are driving WRXes and STis) on the road, and generally give them
plenty of room. Why? Experience and observation tells me their drivers
are far more likely to try to use their right foot instead of their
brain to manuever thru tricky situations. The only "tragedy" when such
drivers crash is that innocent people may be hurt. Otherwise, it's just
Darwin having his jollies.

The only people who race around like a jackass in an STi are ones who think
the people they're pissing off will never see them again. I happen to live
in an area small enough and with few enough STis that my distinctive car is
instantly recognizable around town. Not only do I refuse to drive like an
insane "wannabe" rally racer but if I ever did, I doubt my car would last
the month.

In fact, I don't even allow my passengers to flip the bird, shout, or
otherwise carry on disrespectfully while the drivers around me busily try
to kill each other.

I can only imagine your statement was directed at someone else.. however,
it was originally directed at me, and thus I take exception to your snap
judgements.

They're typical, but honestly.. speed doesn't kill. Driving recklessly does.

Or, to quote a local traffic helicopter pilot, "I see a LOT of crashes
every day. I DON'T see many 'accidents.'"

....from hundreds of feet up, he can see enough detail to make that
determination can he? 'Cause.. you know.. being in a helicopter all day
makes him an expert witness of street-level details. heh

clare at snyder dot ontario dot canada wrote

And most of them would not last very long in the "real world" of
rallying, either.
Posers and wannabees.
AKA aggressive drivers, AKA idiots.

Too many people have bought into municipal anti-"speeder" propaganda. I
never said anything about reckless driving. What too many people seem to be
confused about is the difference between *reckless* driving and just plain
speeding. That is, some people don't think there's a difference between
them, or they think one is a subset of the other.

It *is* possible to do 150/180kph safely, if the road is made for it and
there's plenty of visibility. Heck, some stretches of the Alaska highway
(really amazing stretch of road for STi/WRX by the by.. really a lot of
fun to drive,) are so huge, so wide, so open, and so perfect you can do
265kph and the only thing that happens is the bugs carpet your rad like a
nasty multi-legged mushy.. carpet.

Anyway, take it easy, and try to empathise with your fellow humans a little
more. Cause.. dude.. other people empathising you is the only thing that's
keeping you alive.