Temperature Effects

[Superturnier]

This is a very funny coincidence, since I was doing my own graph two days ago and searched this site if anyone would have published their data, but did not find anything. But a day later this topic appears...

I have been collecting my commuting data over a year and now I wanted to see if my new winter tyres will make any difference.
My trip to work is total 13,7km and I take 3 readings during each trip.
-First after 3,6km of town roads
-Second after a 6,5km highway period @ 80-100km/h
-The last after arriving to my work (3,6km @80 km/h road + town roads)

Also I make notes about the temp, wind, snow, traffic, speed, preheating etc.
I think I can make a thousand graphs with all these variables

This graph I made is from the highway part only.
I was very surprised to see how much the temperature affects to the MPG



Although there's yet only 2 datapoints, it was nice to see that my new winter tyres (Nokian hakkapeliitta 7) are on the better side than the old retreaded "wintercontact allweather" tyres.
I was afraid to inflate the old tyres over 2,5bar, I thought they would explode. There wasn't even any mention about the max pressure.
The Nokians have now 2,7 bar and the really roll much better.

[PaleMelanesian]

Originally Posted by slowmover

Yeah, Corpus Christi to Texarkana via Dallas is almost 600-miles. But you're close to Pittsburg and some nasty [great] hot links. Are you old enough to remember Big Al (at Lone Star Steel)?

And you're outside of an EPA Attainment area, so no "summer gas" either. Prior to reading this site I'd have thought that, say, past 90F that mpg would taper off, maybe even decline.

I'm only 15 miles from Lone Star. I've only been here 10 years, so no I don't know Big Al. Originally from Aggieland.

We actually are in an EPA Attainment area, but it's from industry not from cars. Those coal plants (Martin Lake, Pirkey, Monticello) do the dirty work and they leave our cars alone.

[mcrews]

pale,

Gig'em class of 79

[Diesel_Dave]

I can't see Pale's plot, but it looks like Super's plot is pretty close to 1% per 1 deg C (just a litle less than that).

[gone-ot]

Originally Posted by PaleMelanesian

Pale, I recall you posting this chart earlier (back in 2009?), and I believe that you gave the linear regression equation for the "black"-line too, correct?

[PaleMelanesian]

try this if you couldn't see the other.


It's R^2 about .93. The actual data is much uglier than this (R^2 ~0.25), thanks to real-world things like wind and rain and long or short trips. (and my own driving errors) I averaged all the mpg data points at each temperature to get this chart.

[slowmover]

Aggies, hmmm. I've noticed since being down here (South and South East Texas) that a an Aggie alum sticker and poor driving habits are too often related. Cut's back in front of me too soon on the highway . . Can't park between lines because only knows how to follow front wheels around (no awareness of vehicle starboard and no clue of vehicle pivot point off rear axle) . . likeliest to cut an intersection corner (out-of-lane during turn; enters oncoming lane during turn), etc. . No, not the worst group, but it's especially consistent when it's a pickup. I wait for a basic driving flaw and it's there every time. Conjecture: Ever since the first Aggie doctorate was awarded in recognition of proof that ice is formed of water success must have gone to the heads of even the C students. Or business students (is there a difference?)

Dave, is there a point along the temp chart where changes are made in how the truck is operated? I got you about frost and daylight, and want to be sure I get it about any other changes (since I wind up trying what you've tried, but have no "elbow rest" of daily commutes to back my considerations). The close relationship of temp and mpg, gas or diesel, is really impressive

.

[mort]

Originally Posted by Diesel_Dave

...
40 deg F change results in about a 20% change in mileage. So mileage changes 1% for every 2 deg change. That's pretty significant.

Or like you said 1% per Deg C.
Andd Superturnier's graph,
and PaleMelanesian's graph, which looks a little less steep. Great work!
Although all these seem to be for what I consider short commutes. 10 miles and 14 km. My commute is closer to 20 mi, but my graph would look similar, if...



My question is why? Does anybody vote for higher aero-drag because of denser air? It's a pretty big change, about 15% denser from 40 C to 0 C.
Or do the tires lose pressure, (same density issue)? Or does the engine lose efficiency just from having to start with colder intake air? That's also a surprisingly large effect. Lubricants are stiffer? Some kind of engine warm-up that burns fuel? Is there anything, besides moving, that helps?

-mort

[PaleMelanesian]

From what I've researched (no references right now, sorry), it's mainly air drag and tire friction. From 100F to freezing, air drag increases 10% and tire rolling resistance doubles. Using the calculator, for the average car that means ~30% lower mpg at 35 mph and ~20% lower at 70 mph. You can add on top of that any extra warmup, lube friction, lower tire pressure if you don't keep up with it, etc.

[Diesel_Dave]

Originally Posted by slowmover

Dave, is there a point along the temp chart where changes are made in how the truck is operated? I got you about frost and daylight, and want to be sure I get it about any other changes (since I wind up trying what you've tried, but have no "elbow rest" of daily commutes to back my considerations). The close relationship of temp and mpg, gas or diesel, is really impressive
.

I made a few small changes (full radiator block & oil pan heaters 10 days in, slight route change after day 20, & lower grille block at day 40). It's always hard to tell exactly what impact those mods had, but my opinion is that the temperature change was the most significant thing. Of course, there's always differences in traffic, how I catch red lights, rain, snow, etc. as well.