I'm not a hardcore hypermiler, but just doing little tricks (minimizing throttle/braking, "reading" traffic, maintaining an appropriate speed/distance relative to other cars, etc) makes quite a bit of difference in the commute. I have a small (tiny?) turbocharged car and can get 40-42 mpg on my commute between Denver and Boulder.

In the same sense, I'd like to know how my computer usage is affecting my battery life. Do the extra tabs I have open in chrome matter, or should I bookmark them and close them until I need them? Just because I value one thing over another, doesn't mean the less valued option doesn't come in to play when making a decision.

It doesn't really matter because your gas mileage is likely dominated by things like flooring it down on-ramps.

But 3rd is more efficient in the case you describe.

Those effects are noticeable on my normal commute, where I travel 8 miles and spend most of the time going less than 30 mph, where aerodynamics doesn't matter that much. When I take a road trip (and thus don't have to perform any suicide merges), the difference any of these things makes is quite substantial. My summer tires are each about an inch wider than the tires I have mounted on my old rims, and switching to the narrower tires makes more of a difference in mileage than taking off the roof rack. With the narrow tires and no roof rack, I can get about 36 miles per gallon at 55 mph, and with my winter tires and my roof rack on my car I can't even approach 30 MPG.

For a tech-related example: I prefer to use my phone with the backlight turned all the way up, even though it uses an additional 15% of every full charge, but I uninstalled the Facebook app because it used 3% of every battery just running in the background.

I'm just trying to be efficient in my own way, I'm not competing on efficiency.

A huge part of why my mileage is terrible is because I basically have the worst possible commute for fuel mileage. live in Chicago, which supposedly has the worst traffic congestion in the country. My commute is only about 8-10 miles, but there is a lot of variation in speed. I can go from stopped to 65-75 miles an hour back down to stopped several times on my commute. The commute takes about 30 minutes, and I spend a lot of time idling.

Obviously that is a ridiculously low mileage for a car, even given the conditions. My fuel mileage never dips below 18 mpg for an entire tank, but it rarely goes above 20 mpg unless I leave the city. Looking at similar vehicles on Fuelly, I don't think it's that far out of the norm.

My Impreza is a 2010 OBS, with the 2.5L NA EJ25, and a 4EAT. I think what really kills my mileage is the 4-speed automatic. From what I've read, it's absolutely brutal on fuel efficiency compared to the 5 speed manual. The NA uses a lot more fuel than the turbo when just puttering along as a result of its higher compression (10.0:1 vs. 8.2:1) It's not necessarily a negative - my car is faster off the line than the turbo, especially after sitting in traffic on a hot day.

I know the WRX has a DOHC engine, whereas the 2.5i is SOHC. That probably makes some difference in efficiency, though I don't know how much.

On top of that, I almost always have my roof rack on if I'm driving in the city, and I usually have a bike rack mounted as well. Plus, I have the hatchback, which I've heard also impacts mileage, though I have no idea if that's true.

I've also replaced the somewhat narrow stock-all seasons with wider and softer tires summer tires. I run high sidewall winter tires on steel rims in the winter, which weigh a lot more than the stock alloys/all seasons.

Regardless, the Impreza really sucks at city mileage compared to other cars because of the added weight and drivetrain losses of the AWD. (As you probably know) It's really no surprise the 2.5i and 4EAT have been replaced by a much smaller engine coupled to a CVT.

The hatchback probably doesn't impact your fuel mileage much. I don't think the difference between DOHC and SOHC is going to have any measurable impact on fuel mileage either. Nor would I assume that a compression ratio change does that much. Your final drive ratio is probably the most significant impact. Additionally how much time you spend in "lockup" mode (where the fluid clutch is essentially disengaged and the engine crankshaft is directly connected to the driveline) is a major contributor. The roof rack absolutely impacts fuel mileage as Consumer Reports demonstrated: http://www.consumerreports.org/cro/news/2013/07/tests-show-b...

Anyways, I take the highway to work, and I take a short stint on a highway and then surface streets on my way home. On my way home I run in to something like 40 stop signs. Pretty much every intersection has a four way stop for a few miles of my commute.

I can actually quantify how much the roof rack affects mileage, because I track whether I have it on my car or not in addition to my mileage.

That just screams "hybrid" to me. Wouldn't a hybrid or EV be the perfect vehicle for that scenario?

The "shift up" recommendations to me seem like an attempt to replicate the ideal conditions under which the official efficiency tests are done - and we all know about /those/ figures...

You don't have to measure for yourself at all. The things you can do to save gas are well understood. If you generally just don't trust others' fuel efficiency guidance, I'm not sure why you'd trust someone else's mpg estimate either.

I get the logical appeal of the immediate feedback MPG meter, but I'm not clear how accurate these things are (vs meters on the gas pump, which are regulated to be within a tight spec). I'm also not clear how useful the MPG right now is vs the MPG over the past hour. I've seen only one car that let me reset the MPG meter and measure for an arbitrary period of time that I control, and I still have no idea how accurate it was. (Yes, I'm sure there is more than one car with this feature. I've only seen it once.)

Again, I just generally don't buy that instant (actually averaged over some amount of time that you don't control, with some accuracy that is likely not guaranteed) MPG estimates are all that useful. Are you dedicated enough to efficiency that you'll drive without A/C in the summer to see if it's better but you somehow don't care enough to bother recording actual gas usage? Who are these people willing to drive without A/C to save a MPG but too lazy to confirm that it really works? Or realistically is this one of those things where you turn off the A/C, glance at the MPG estimate and see it went up from 20 to 22, and assume that you've got a definitive answer despite not knowing anything about the margin of error for the MPG estimate?

On one hand, instantaneous mpg is seriously misleading. To me, accelerating efficiently means maximizing the amount of acceleration I get per unit of fuel—doing that does NOT maximize instantaneous mpg, but ideally finds the optimal point on the fuel-consumption-rate*time graph that you actually care about.

On the other hand, real-time feedback is probably better for the not-exactly-scientifically-rigorous way people learn, and it can be useful for noticing unexpected behavior not covered by intentional experiments.

A realtime unit-less fuel efficiency gauge in a U-Haul clued me into non-ideal behavior from the automatic transmission climbing hills. Feedback from this dumb gauge caused me to adjust my driving, which meant only my first tank of gas lasted way less time than expected.

It's also apparently pretty common for hybrid-car drivers to adjust driving patterns to improve mpg, partly because the car gives rapid feedback - gamification in real life! - but there's probably also some selection bias, as people who buy high-mpg vehicles are more likely to be concerned about fuel efficiency.