[colorado723]

Is this accurate for fuel mileage while at highway speed? Or does it account for stopping as well. My cars max HWY mpg should only be 28, I beleive, so why does it sit at high 30's. My tests were 20 mile intervals to account for hills as well.

A/C on drafting



No A/C drafting


No Draft w/ A/C


If I'm completely wrong, at least I can verify that you only gain about 4mpg at most.

[Tom K.]

Have you checked the OBC accuracy by repeatedly comparing actual mpg (miles driven divided by gallons consumed) with the computer readings over a number of fill ups?

The OBC in my '03 Z4 was about 7% optimistic and my '07 E91 reads about 4% high. Highway cruising nets about 28 to 30 true mpg for the MT 328i.

Tom

[Douche]

Lol, it's more economical when the check engine light is on...

[Eddien123]

I can honestly tell you that there's no way you're getting 35 mpg on the highway. The best I've seen was 33 and that didn't last long. Also, the revs you see at 65 are mine around 75, why is that?

[Douche]

Originally Posted by Eddien123

I can honestly tell you that there's no way you're getting 35 mpg on the highway. The best I've seen was 33 and that didn't last long. Also, the revs you see at 65 are mine around 75, why is that?

You drive an automatic transmission.

[drewnel22]

Originally Posted by Tom K.

Have you checked the OBC accuracy by repeatedly comparing actual mpg (miles driven divided by gallons consumed) with the computer readings over a number of fill ups?

The OBC in my '03 Z4 was about 7% optimistic and my '07 E91 reads about 4% high. Highway cruising nets about 28 to 30 true mpg for the MT 328i.

Tom

+1

[colorado723]

I used to do that in my old cars that didn't calculate miles per gallon. I'm bummed out that this one is that inaccurate . Looks like I have more testing to do . It double bums me out that drafting behind trucks doesn't increase your fuel mileage as much as I thought either. Science is being mean to me today .

[Douche]

Originally Posted by colorado723

I used to do that in my old cars that didn't calculate miles per gallon. I'm bummed out that this one is that inaccurate . Looks like I have more testing to do . It double bums me out that drafting behind trucks doesn't increase your fuel mileage as much as I thought either. Science is being mean to me today .

Drafting behind trucks does help.
But if you realize how vortex works, you'll quickly realize that for it to be a draft you have to be before the vortex. Thus, almost touching the trucks bumper. That is too dangerous.

If you follow it close you are just catching the vortex and not drafting. That is WORSE than standing clear of trucks altogether, because now you are getting of the air coming into a "punch" in front of your car.

Drafting is nonsense.

[jt335i]

The MPG numbers don't seem strange at all. A 4 MPH gain while drafting seems about right, but it also depends how fast you’re going.
Non-turbo 325s and 328s, I've noticed, can get over 30MPG on the highway non-drafting. My mom and pop have a 2012 328 vert and the average MPG is between 30-32.
I'm looking at your speed, the reason why you're getting mid to high 30 MPG range (drafting w and without A/C) is because you're traveling at 65 MPH. Of course, the faster you go (non-drafting w A/C) your MPG will go down to closer to 30 MPG. And yes. The average will be affected by how frequently you stop and go because, of course, acceleration and also how much you "gun it" to get up to speed.

I’ve been on several long road trips in my 335i and being that it is a TT, mine averages between 28-29 MPG on the HWY travelling at an average of 70 MPH (non-drafting). When drafting at the same speed, it has gotten 32+ MPG. I’ve travelled at 75 MPH getting between 27+MPG (non drafting) and when drafting it got close to 31 MPG.

[AdamN52]

On my last fill-up I was way out in the country, and on the trip home I saw below 6.5L/100km avg while cruising at ~90km/h on country roads.
(That's about 36mpg going ~60mph, for the Americans)

My car has great economy when cruising... city driving & traffic is whole different story. lol

Also, my OBC is typically quite accurate when I check it using my real volume of gas at the pump over distance driven.

[colorado723]

It seems like the computer making the calculations is somewhat accurate to this model that Mythbusters had tested. I guess 50 feet feels a lot closer when you are at 65mph. Also their tests were at 55mph, which is probably what helped their model. The only part that is significantly off on my car is the actual calculation of mpg, not the gain.

[lichtgelb]

I get high 30's at 70mph with a nice tailwind and while drafting a truck. You know you are in the draft when you barely hear any "buffeting" and you can feel the air smooth out. Unfortunately this spot is usually at a point where you can't see the trucks rear view mirrors. The other problem is trucks are traveling far too slow and can't keep a constant speed up shallow grades. Since I drive a BMW I'll leave drafting to the Prius driving hypermillers.