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Thread: Winter Fuel Econcomy Reply to Thread
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Topic Review (Newest First)
01-23-2013 09:01 AM
Pinion Dominion Today I drove my usual 4.1km to work. The temperature outside was -19 degrees Celsius.

When I started my car the distance to empty was 401km. When I got to work the distance to empty was 380km! (When I fill up to max, distance to empty is 540km)

Now I always found the distance to empty was a pretty accurate number as it seemed to be tailored for city driving. For example, when I drive 120km (90% highway) to visit family, the distance to empty goes down at max 80km.

Is there any tips you guys have to improve winter fuel economy?
12-07-2012 11:17 AM
gkirk
Quote:
Originally Posted by jsr72 View Post
To produce an identical level of aerodynamic form drag, if the air density is increased then the velocity must correspondingly decrease.

In highly idealized situation if the air pressure happens to be the same at two different temperatures, then the new velocity is simply the original velocity times the square root of the new temperature divided by the square root of the original temperature. (Use absolute temperatures in the calculation)

For instance, if a vehicle is traveling 70 mph at 70F, then it experiences the same amount of form drag at 67.3 mph at 30F.
I think the ideal case is pretty good - without putting the car in a wind tunnel and checking it.

:)
12-06-2012 06:23 AM
MelloYelloTi Last 2 tanks have averaged to about 27 to 28 mpg overall. Down about 4 mpg from about a month ago. Still not to bad as my Sable was getting 16 to 17 mpg overall in the same temps..
12-03-2012 10:17 PM
jsr72
Quote:
Originally Posted by GoShockers View Post
Also, how much of an impact on fuel mileage does cold air cause? Let's take away the fuel aspect and perhaps even the warm-up period. Does the colder, denser, "heavier" air cause enough problems aerodynamically to make a difference?
To produce an identical level of aerodynamic form drag, if the air density is increased then the velocity must correspondingly decrease.

In highly idealized situation if the air pressure happens to be the same at two different temperatures, then the new velocity is simply the original velocity times the square root of the new temperature divided by the square root of the original temperature. (Use absolute temperatures in the calculation)

For instance, if a vehicle is traveling 70 mph at 70F, then it experiences the same amount of form drag at 67.3 mph at 30F.
12-03-2012 07:48 PM
SydneyRoo
Quote:
Originally Posted by jdetzel View Post
According to here:
http://1010tires.com/tiresizecalcula...?action=submit
There would be about a 6% increase with the smaller tires.

In other words if you traveled 100 miles your odometer would actually show 106 miles.

It actually says 5.833%, which @ 30mpg would show as a 1.7mpg increase.

That is just what that site says, I do not actually know how to do any of the tire size calculations.
Oops I goofed. The factory Michelin PS3s are 235/40/18.
I reran the calc and it said the 16s would now read 2.1% fast. That's pretty negligible IMO (ie, actual speed is 100 km/h but speedo reads 102).

The 18s are way too fat for this car, but they are awesome. My fuel eco definitely is better with the skinnier winter tires on (while it's still not actually winter yet, most days are above freezing still). Maybe when the 18s wear out I might pick up some factory 17s, just to have a hope at actually getting 40 mpg for once :p
12-03-2012 12:58 PM
gkirk Don't forget that tire pressure will drop a bit with temperature too. Not sure exactly how much it will drop, but I found a reference that it is about 1psi / 10 degrees F.

So if you inflated them at 70F, they will be 3-4 psi lower at 32F. That can cause a noticeable drop to gas mileage.
12-03-2012 12:05 PM
PDQEagle I've gone thru 7 winters in massachusetts, and drive the same commute each day, with little weekend travel. My commute is not highway, but I can go 45-50 most of the time, with few stops and slowdowns. Summer I get a consistant 30-31 mpg, winter consistant 27-28, like clockwork.
The cold effects in several ways. All fluids (oil and grease) are thicker so offer resistance. Tire pressure goes down, if you haven't checked it. My previous Eclipse with awd, in summer backing up out of the drive, clutch in, it would coast. In winter, definitely stop coasting much quicker.
Gas gets vaporized poorer so less efficient burn (regardless of electronics), engine warm up even if you start off rightaway, traffic slowdowns.
The change from summer to winter gas is mostly to ease vaporization, and I can't believe the little power difference would make much difference
12-03-2012 10:18 AM
jdetzel
Quote:
Originally Posted by SydneyRoo View Post
I've checked it out, the rotations ratio is negligibly close. Factory 18s are 235/45/18 and my winters are 205/55/16
According to here:
http://1010tires.com/tiresizecalcula...?action=submit
There would be about a 6% increase with the smaller tires.

In other words if you traveled 100 miles your odometer would actually show 106 miles.

It actually says 5.833%, which @ 30mpg would show as a 1.7mpg increase.

That is just what that site says, I do not actually know how to do any of the tire size calculations.
12-03-2012 09:57 AM
SydneyRoo
Quote:
Originally Posted by ransil View Post
Are the tire rotations per mile the same for both sets of tires? Could be a calculation issue.

Sent from my Galaxy Nexus using FF Mobile
I've checked it out, the rotations ratio is negligibly close. Factory 18s are 235/45/18 and my winters are 205/55/16
12-03-2012 09:41 AM
ransil
Quote:
Originally Posted by SydneyRoo View Post
My fuel economy has gone up by 2 mpg ever since I took my summer 18s off and put my winter 16s on. Man those 18s kill my fuel mileage..
Are the tire rotations per mile the same for both sets of tires? Could be a calculation issue.

Sent from my Galaxy Nexus using FF Mobile
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