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      11-05-2012, 05:16 PM   #1
Hooy
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Drives: 2008 328i Coupe
Join Date: Sep 2009
Location: Houston, TX


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2008 E92 328  [2.50]
Epic MPG increase?

I am unsure of what's going on, but my MPG is possibly getting very good compared to before. I reflashed my car with AA's stage 2 as well as put on 17x8" wheels with all season tires a week ago. Here is an INCOMPLETE breakdown of my setup and results.

My first gas tank:
~60 miles of breaking the tune in in the city (WOT, lots of stop-go)
~175 miles of highway cruising (no cruise control because mine is broken)
~80 miles of mixed driving. This includes 20 minutes of WOT road course where I overheated my car and held revs at 5000+ RPM for 10 minutes at a time. Also includes 4mph stop-go traffic.
14.5 gallons used
21.8 calculated MPG

My 2nd tank (IN PROGRESS):
~55 miles of city driving. LOT of stop and go, very short distances, oil almost never fully warmed
~175 miles of highway @ 80+mph with windows/sunroof down.

The progress SO FAR:


Before:
19x8.5, 19x10.5" ADV.10 TrakFunction (51 pounds, rear, with TPMS) (unknown front weight)
235/35, 265/30 Nitto INVO summer tires, 34/36psi
Eurocharged custom dyno tune
315 miles per tank w/ city driving
370 miles per tank with 340 of those miles being 100% highway

After:
17x8" square OEM Style 157 (46 pounds combined, no TPMS)
225/45/17 Continental DWS all-season tires, 40psi
12mm H&R spacers (unknown weight)
Active Autowerke updated canned tune (stage 2)

I will be weighing the ADV.1 + Nitto combo tonight, as well as the 157+DWS+12mm spacer combo. If the weight is dramatically different, that could explain things.

UPDATE 1:
I weighed the 17's and rear 19's. The weight difference is surprisingly small... 19x10.5+265 tire = 51 pounds, 17x8+225 tire=46 pounds. How much can 5 pounds of unsprung weight decrease MPG?? I do realize that most fuel is burned getting off the line and can see how 5 pounds can affect it, but this seems a bit much.

Also, I drove 8 miles and my estimated range went from 300 to 234.

UPDATE 2:
I completed the tank. Aside from 175 miles of cruising, the other 200 were almost entirely stop & go city driving. 379.6 miles to 15.1 gallons - 25.14mpg. That is BETTER than 350 miles of cruise control on my ADV's.

UPDATE 3:
I've completed a couple of tanks and they are all within 22-26mpg with a lot of gridlock traffic driving mixed in with 150-170 miles of cruising. My last tank was 22.8mpg with 170 miles of going 85-90mph + 45 minutes of road course.
My current tank is showing massive gains.
The 6AT loves 60mph. This is ~140 miles of nothing but 60-65 with no cruise control or braking.

Tires set to 38/40 cold psi.



CONCLUSION:
Smaller contact patch, less aggressive compound (all season), and less overall weight have DRAMATICALLY increased my mpg.
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Last edited by Hooy; 11-20-2012 at 03:19 AM.