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      11-05-2012, 05:16 PM   #1
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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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      11-05-2012, 06:15 PM   #2
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Perhaps the AA tune is a bit better. Since you've had both, can you comment on if the AA stage 2 is better than the EC tune?
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      11-05-2012, 06:16 PM   #3
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Perhaps the AA tune is a bit better. Since you've had both, can you comment on if the AA stage 2 is better than the EC tune?
I really don't want to get into that in this thread. I will report back with wheel weights by tonight.
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      11-05-2012, 07:28 PM   #4
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I know the stock wheels are heavy also, but I gained 3-5mpg when I was on my stock 161s for a few weeks. When I put my v710s back on it shot back down.
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      11-05-2012, 07:36 PM   #5
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Are you obtaining your mpg by trusting the car's computer or by actually verifying miles traveled and gallons of fuel used?
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      11-05-2012, 08:48 PM   #6
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      11-05-2012, 09:15 PM   #7
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not sure it's wheel weight. i averaged 23.0 mpg with ~32lb wheels and now get 23.2 mpg with ~21lb wheels. same tires. feels a lot more nimble though...
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      11-05-2012, 09:54 PM   #8
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those 265 summer tire vs 225 all season alone could kill your mpg already
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      11-05-2012, 09:54 PM   #9
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Quote:
Originally Posted by Johnny D View Post
I know the stock wheels are heavy also, but I gained 3-5mpg when I was on my stock 161s for a few weeks. When I put my v710s back on it shot back down.
Quote:
Originally Posted by CombatNinja View Post
Are you obtaining your mpg by trusting the car's computer or by actually verifying miles traveled and gallons of fuel used?
I am calculating it.

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Originally Posted by Gunners_Mate View Post
It's a conspiracy, man!!!


Quote:
Originally Posted by plokij View Post
not sure it's wheel weight. i averaged 23.0 mpg with ~32lb wheels and now get 23.2 mpg with ~21lb wheels. same tires. feels a lot more nimble though...
The 157 + DWS weighs ~46 pounds. I am going to weigh the ADV1's soon.
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      11-05-2012, 10:00 PM   #10
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those 265 summer tire vs 225 all season alone could kill your mpg already
yes, that is my suspicion! Weighing them soon.
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      11-05-2012, 10:48 PM   #11
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Updated with wheel weights... Results are surprising. how can 5 pounds affect my mpg so much?
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      11-05-2012, 10:57 PM   #12
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Are you obtaining your mpg by trusting the car's computer or by actually verifying miles traveled and gallons of fuel used?
this
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      11-06-2012, 12:55 AM   #13
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could also be a difference in overall tire diameter between the 19s and the 17s.
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      11-06-2012, 03:24 PM   #14
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could also be a difference in overall tire diameter between the 19s and the 17s.
that. you've got more rotating mass per corner with 19's + tires VS your 17s + tires. and you can't just look at one corner. you have to add up the weights in all four corners. also, your car is lower with 17s VS 19s so it could reduce drag.

and although the mpg calculator in our cars are nice, just keep track of how many miles you run on a full tank (or whenever you fill up). that'll give you a more accurate calculation.
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      11-06-2012, 03:32 PM   #15
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Exactly. The width of the tire alone creates more resistance since the contact patch is so much larger.
Another major factor is the chemical compounds in the rubber. "Eco" tires may sound like their production might have a smaller carbon footprint or something, but they're called that because their rolling resistance is reduced because of the chemicals in the tire. Porsche and BFG engineered a sort of eco tire that still grips like hell for that new hybrid 918 or whatever it's called. I'm curious to see what a set would run for.
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      11-06-2012, 04:16 PM   #16
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FWIW, I recently switched out the heavy RFTs on my e91 328 for very light Conti DWs. I think the weight were around 27F, 29R for the RFTs and around 21F, 24R--getting close to 25 pounds of rotating weight as far from the hub as possible. My mpg went up by anywhere from 0.5mpg to 1.2mpg per tank. Nothing like what you are seeing. Of course mine were stock sport pack sizes...
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      11-06-2012, 04:30 PM   #17
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Quote:
Originally Posted by just4kickz View Post
this
Quote:
Originally Posted by J-Spec Dan View Post
that. you've got more rotating mass per corner with 19's + tires VS your 17s + tires. and you can't just look at one corner. you have to add up the weights in all four corners. also, your car is lower with 17s VS 19s so it could reduce drag.

and although the mpg calculator in our cars are nice, just keep track of how many miles you run on a full tank (or whenever you fill up). that'll give you a more accurate calculation.
Guys, I stated that I calculated these fillups. The trip computer was not used, even though it was only 0.1 mpg off.

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It's not the wheel weight as much as the rolling resistance from having a wider tire, this is why economy cars have very narrow tires
This is the conclusion i've come to as well. It sucks because wide is way, way, way better looking.

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Exactly. The width of the tire alone creates more resistance since the contact patch is so much larger.
Another major factor is the chemical compounds in the rubber. "Eco" tires may sound like their production might have a smaller carbon footprint or something, but they're called that because their rolling resistance is reduced because of the chemicals in the tire. Porsche and BFG engineered a sort of eco tire that still grips like hell for that new hybrid 918 or whatever it's called. I'm curious to see what a set would run for.
I love new tire technology and can't wait for some new stuff to come out, especially the Z2 Star Specs

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FWIW, I recently switched out the heavy RFTs on my e91 328 for very light Conti DWs. I think the weight were around 27F, 29R for the RFTs and around 21F, 24R--getting close to 25 pounds of rotating weight as far from the hub as possible. My mpg went up by anywhere from 0.5mpg to 1.2mpg per tank. Nothing like what you are seeing. Of course mine were stock sport pack sizes...
I don't know why the difference is SO dramatic. I will have to see when I actually finish the tank since it's all speculation right now.
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      11-06-2012, 07:02 PM   #18
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Quote:
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FWIW, I recently switched out the heavy RFTs on my e91 328 for very light Conti DWs. I think the weight were around 27F, 29R for the RFTs and around 21F, 24R--getting close to 25 pounds of rotating weight as far from the hub as possible. My mpg went up by anywhere from 0.5mpg to 1.2mpg per tank. Nothing like what you are seeing. Of course mine were stock sport pack sizes...
how did those non-rft work out for you beside better mpg? is it the purecontact that u got?
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      11-06-2012, 07:30 PM   #19
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Couldn't have been happier after the switch. Better ride, less noise, less tramlining, better acceleration, better fuel economy and better looks all at less than half the cost of a new set of runflats. The only compromise, if you will, is a slight reduction in turn-in response. The rock-hard RFTs seemed to act like a big 20" wheel almost--no sidewall flex at all. The 17" sport pack tires have a beefy sidewall that would flex ever so slightly during aggressive turn-in. More than worth it all in the end. I noticed the upsides 99.9% of the time and experienced the downside for the remaining 0.1% of my time in the car.

I got the Continental ExtremeContact DW, an ultra high performance summer tire. Sized 225/45R17 front and 255/40R17 rear.
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      11-06-2012, 07:39 PM   #20
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Guys, I stated that I calculated these fillups. The trip computer was not used, even though it was only 0.1 mpg off.
hah, my bad man. but yeah, if you've got a greater contact patch, more mass, more rolling resistance, mpg will go down.
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      11-06-2012, 07:57 PM   #21
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alignment could also be a big part of it, especially if you had a lot of negative camber to fit those rear ADV.1's
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      11-06-2012, 08:01 PM   #22
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alignment could also be a big part of it, especially if you had a lot of negative camber to fit those rear ADV.1's
Alignment is at stock specs, the tire wear is totally even after 10 months. I think it's just the 328's lack of torque and the big ass tires.
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