Best speed for best milage?

I have not done this on a Forrester but most consumer cars and trucks get the best at a much lower speed...55-65MPG. Let us know what you find if it doesn't bore you to death doing the experiment. TG

It's hard for me to find out, since 75 mph is well over the speed limit here in NZ, but FWIW when I travel between Wellington and Auckland I have a choice of doing 80 - 105 km/h in heavy traffic on the wide and fairly straight SH1, or finding a hillier, more twisting, narrow tertiary road and taking a lot of corners at 80 km/h and doing 120+ km/h on the straights.

I seem to get about the same MPG either way, or maybe even slightly better on the back roads.

It's *very* noticable that hills that require a bootfull of gas in top gear (or even a downchange) at 100 km/h can be taken with only the lightest of pressure at 120+, so I can well imagine that 120+ might be more economical as well.

Unfortunatly, with only a 4 speed auto, forcing it into 3rd all the time isn't really an answer, since you end up at 4000 RPM, not 3000, and that doesn't feel very economical at all (it would be 160 km/h in 4th).

-- Bruce

Best mileage would be zero. ;-)

According to the cartalk guys, the speed you're going right after you've shifted into the highest gear is the most fuel efficient. Typically around 45mph. If you could conceivably drive that speed in that gear for the majority of the time, you would be getting the best mileage.

No, that would be the worst possible, assuming that the engine is actually running.

Sometimes I shift into top gear at 50 km/h, and sometimes at 150 km/h. Which should I pick?

I probably shift into top gear most often at 109 km/h, that being the highest speed consistent with not getting a speeding ticket in a 100 km/h zone. If not for that constraint, I'd probably shift at 120 km/h, in line with the previous poster's posited 75 mph.

-- Bruce

I've heard that the best economy on a four stroke internal combustion engine is when the engine is being lugged at low RPM. Lots of throttle, low RPM. This is the best efficiency for the ENGINE to make power, and has nothing to do with wind resistance. In theory, lugging the engine at low RPM in top gearing would produce the best MPG. The engine is producing the most power for the least gas, and running that power through the highest gear in the transmission.

Unfortunately, lugging an engine at low RPM with full throttle is also supposed to be one of the hardest things you can do to the engine, so your real economy may vary.

What that means is the fastest the wheels can go with the least amount of RPMs, which would typically be the slowest speed in the top gear.

YMMV

Here's an EPA (U.S.) guide on fuel economy:

There's a graph in that document that indicates the best mpg will be achieved at a speed of 45 to 55 mph. That's probably the standard government line, though, not taking all the variables into account. You can also get the standard EPA mpg figures for U.S. cars of various makes, models, and years at that site:

C. Brunner

By experience in my 2000 Subaru Outback, with the 4-cylinder boxer engine, my best gas mileage occurs when I'm driving between 45 and 70 MPH. Over 70 and it drops off noticeably. Under 45, and I'm usually in stop-and-go traffic, which gives so-so gas mileage. I just changed jobs, and my commute went from 22 miles down to 8 miles, one way. My miles-per-gallon also went down, from 25 to 20, cause the old commute was on Interstate highway and the new commute is in town.

If you are rear-ended doing 50mph in a 70mph zone, you will learn that you haven't considered 'all' cost factors when computing the most economical speed. :-)

I really dislike being pushed through unfamiliar cities when traveling and try to avoid being in such situations at peak travel hours. I find it's best to try to stay out of everyone's way and not impede those who 'know' where they are going, concern myself with staying alive, and worry about fuel economy when I'm back on the open road.

I would hope most drivers would agree with this and be tolerant of those who are 'unable' to face this fear factor due to age, experience etc.

BoB