BMW M3: "The optimal speed for fuel economy in this car seems to be around 80mph"

[obioban]

Sorry for the weird edits, the forum won't let me use links, pics, or emoticons till I'm at 5 posts :P

[AeroModder]

I've been interested in mapping the speed vs. fuel economy in my car for a while now, but I don't have the proper instrumentation. Whenever I drive on the freeway, my tank MPG seems higher than usual.

I'd be interested in seeing you test the MPG from 50+ in both 5th and 6th gears.

[bgd73]

interesting thread, can't recall spotting this one.

My old sube is bizarre with highway too...
3600=92mph, and it is in absolute tippy toe on the throttle heaven...bouncing around 30s mpg with a sucking hole in the top of the tank (it used to be in the 40s there). I am from 87-92mph with a sucking hole... it is mythologically hilarious.

the m3 is no surprise with a deep overdive on a power to weight ratio that is quite high.

I like the route of faster and hyper mile. That is the ultimate is it not?

A giant lesson is deciphering a tractor trailer...they are the same all the time, weight and speed. If the engine is content at spoeed, lean games can play and not hurt.

[KJSatz]

It would be neat to see it redone including lower speeds. Would 6th gear be too high for 50mph? I think you could at least try that as well.

[MetroMPG]

Hi obioban -

I'd love to see controlled as possible testing at lower constant speeds. I'd bet a dollar fuel economy will improve as speed drops, right down to just above lugging RPM.

(Feel free to post a couple of "filler" posts to get full forum permissions. It's there so we can spot spammers and obviously you're not one.)

---

Since posting this thread originally, I had a chance to take a 6-speed, 505 hp Corvette Z06 out to collect info for a speed vs. MPG chart:

Tested: speed vs. MPG, 2008 Corvette Z06 (505 hp)

In a nutshell, the slower, the better.

[numbthumbs]

I have achieved (over a full tank of gas) 32mpg when setting the cruise at 50mph on my trip to work and back which is ideal for gas mileage (Lancaster, CA to Edwards AFB). It is a flat stretch with no turns or stops. My tires have more drag than stock because of the size 315s in the rear and 275s up front and I am only running 35psi in them because when I jack them up to 50psi they wear in the center. Pretty remarkable because 6th gear is not really an overdrive in this car (0.85) with a 3.62 final. At 50mph I think I am taching 1750rpm. I will try 5mph increments to see what the best that I can achieve is. I can confirm the numbers at 80mph also. I get around 28mpg which is not bad at all for 333hp normally aspirated 3400lb car. I would like to note that I get some crazy looks when cruising at 50mph in an M3 when the speed limit is 70mph