Fuel Economy

[enkid]

More things I've noticed using the SGII and different driving styles and road conditions:

After coasting down the same hills in neutral hundreds of times over different weather conditions, I can state with confidence, that the temperature's effect on the rolling resistance of the tires significantly impacts fuel economy.

While it's common knowledge that cold weather is bad for FE, I've come to the conclusion its mostly due to: 1. Increased warm up time, especially when the temp is below freezing; proportion of warm-up time as part of trip time is larger. 2. Rolling resistance is the greatest of all temperature FE effects after the motor is fully warm.

Where to go from here:

Research tire rolling resistance?
I've never seen it listed as a parameter, but I suspect
1. High performance tires are "stickier", and therefore worse for FE.
2. Narrower tires and tires with a smaller contact surface (perhaps even snow tires) are better for FE.
3. Are southern/tropical region OEM tires different from temperate or arctic region OEM tires? If so, is it due to a need for different temperature ranges? If so, does this include rolling resistance performance? Do ratings standards organizations mandate that the OEM state which tires are going to be used in different markets/regions, etc?
4. Research optimum tire pressure for temperature & FE. Cruising with under inflated tires is definitely worse, but what is optimum? Cold air decreases air pressure and stiffens rubber, rolling resistance creates heat, heat increases air pressure, higher pressure decreases rolling resistance, etc

Possible mods - My first thought was to redirect the air intake to pull air from inside the cabin, but lowering the cabin pressure might create a carbon monoxide hazard. An alternative might be to cut a hole in the air intake duct between the inlet and the filter so it gets more air from behind the radiator & duct-tape the hole in Summer. I suspect this won't decrease the warm-up time by much (if at all) because hot water doesn't flow through the radiator till the motor is warm. Probably the best thing for cold weather FE would be a block heater to decrease warm up time...and perhaps narrower tires.

Scangauge Calibration

Speed & Miles driven - My SG registers about 1/6 of a percent longer distance traveled per tank than the ODO. Adjustment unnecessary.
Fill tank - correction adjustment ranges from -3% to -6%.

Fairly aggressive hypermiling, but without shutting the engine off while moving, coasting at idle instead of DFCO tends to make the SG say the FE is better than actual, and a -6% fill adjustment corrects it to within a percent.

Less aggressive hypermile, and increased use of DFCO, SG still says FE is better than actual, but less so, and -3% fill adjustment corrects it to within a percent. This is my usual mode.

Driving aggressively in commuter traffic, idling at stops, hundred mile trips in the rain, etc, and SG fill adjustment will want to be around zero.

Last winter, the SG fill adjustment was consistently around -7 percent, and my FE was around 40-43 MPG depending on how cold it was. Since then the SG fill adjustment has drifted to around -3%. I don't know if the difference is because of temperature, motor break-in or both.

32560 Miles, 693 gallons, one year (4 seasons) average FE 46.98 MPG, 90% highway, manual sedan, no mods, Goodyear Eagle GT OEM tires, Rhode Island (sea level).

[voodoo22]

Originally Posted by enkid

While it's common knowledge that cold weather is bad for FE

I know what you mean. With a lot of early morning driving in weather which is about 15 degrees colder than it's been, seems like I'm taking at least a 5% hit.

[Ferret_san]

Bahhh.... Drive it like you stole it.