Gas mileage vs. speed

Gizm0 · 08-07-2013, 12:25 PM

Does anyone know if and where I can find such a curve for our cars? Especially interested in the e92 335i 6MT... Some cars are more fuel efficient going 40mph, others get better gas mileage going 65mph, and I just want to know where the "sweet spot" is on our cars.

See below an example I did quickly to show what I'm after.

wwc310 · 08-07-2013, 12:35 PM

im curious as well. I was under the impression that RPMs and gas mileage would show a better comparison

Gizm0 · 08-07-2013, 12:39 PM

Quote:

Originally Posted by wwc310

im curious as well. I was under the impression that RPMs and gas mileage would show a better comparison

Cruising at 2500rpm in 1st gear and 2500rpm in 6th gear won't give you the same gas mileage... It's speed related, assuming you are cruising using the most fuel efficient gear at all speeds.

Gizm0 · 08-07-2013, 12:50 PM

It would be a really simple exercise to do. Just find a flat road, cruise at different speeds, use the instant MPG on the dash and record a bunch of data points and then make a curve with Excel. I'd do it if I could, unfortunately there are no flat roads where I live... But if someone in here who lives in the flat lands feels bored...

I did however notice on a road trip down to GA that my car seems to achieve better gas mileage around 70mph than 60mph...

24601 · 08-07-2013, 01:03 PM

I'd like to see this too! Good question Gizm0.

Oddly it seems I do best at 80.

wwc310 · 08-07-2013, 01:39 PM

Quote:

Originally Posted by Gizm0

Cruising at 2500rpm in 1st gear and 2500rpm in 6th gear won't give you the same gas mileage... It's speed related, assuming you are cruising using the most fuel efficient gear at all speeds.

sorry forgot to add that part about gear selection.

bhmax16 · 08-07-2013, 01:59 PM

Too many other factors come into play. You may be able to get in the ballpark, but windows up vs. windows down, AC on vs. off, the outside ambient temperature, etc... will all affect the final result for the user.

NemesisX · 08-07-2013, 01:59 PM

Quote:

Originally Posted by MY13E92M3

I'd like to see this too! Good question Gizm0.

Oddly it seems I do best at 80.

In my experience the sweet spot for most cars is around 55-65 MPH.

joelk01 · 08-07-2013, 02:22 PM

Quote:

Originally Posted by NemesisX

In my experience the sweet spot for most cars is around 55-65 MPH.

Downhill

Gizm0 · 08-07-2013, 02:25 PM

Quote:

Originally Posted by bhmax16

Too many other factors come into play. You may be able to get in the ballpark, but windows up vs. windows down, AC on vs. off, the outside ambient temperature, etc... will all affect the final result for the user.

I agree that there are many factors that will affect the results, but they won't affect them by THAT much... I doubt the two same cars running in two different conditions will lead one to be fuel efficient at 45mph and the other at 70mph... they may be off by a few MPH at the most...

Snow King · 08-07-2013, 02:41 PM

I would think that the earliest speed you can shift into the last gear (with low RPMs) will get the best MPG. Unless you have an M3, the final drive is calibrated for high MPG (overdrive) rather than performance.

Gizm0 · 08-07-2013, 02:43 PM

Quote:

Originally Posted by Snow King

I would think that the earliest speed you can shift into the last gear (with low RPMs) will get the best MPG. Unless you have an M3, the final drive is calibrated for high MPG (overdrive) rather than performance.

Yeah, I know that, and I often skip gears to save fuel too... I often do 1-2-3-4-6 or 1-2-3-6, but here I'm trying to determine the best efficiency spot of the car at constant speed, not during acceleration.

yarviinn · 08-07-2013, 02:43 PM

Quote:

Originally Posted by MY13E92M3

I'd like to see this too! Good question Gizm0.

Oddly it seems I do best at 80.

Accurate

Best MPG @ 80 lol

wesyee · 08-07-2013, 02:55 PM

Estimates based on cruise control readings:
55-60 MPH - 40 MPG
65-70 MPH - 32 MPG
75-80 MPH - 29 MPG

cuiter23 · 08-07-2013, 02:57 PM

coasting in neutral downhill

iBoost · 08-07-2013, 02:58 PM

If i cared about mpg, i would be in a Prius.

jk interesting topic

Gizm0 · 08-07-2013, 03:12 PM

Quote:

Originally Posted by cuiter23

coasting in neutral downhill

Actually you'd consume more gas in neutral than if you were in gear...

Gizm0 · 08-07-2013, 03:12 PM

Quote:

Originally Posted by wesyee

Estimates based on cruise control readings:
55-60 MPH - 40 MPG
65-70 MPH - 32 MPG
75-80 MPH - 29 MPG

Thanks man! These are your actual readings? 6MT or AT?

cuiter23 · 08-07-2013, 03:14 PM

Quote:

Originally Posted by Gizm0

Actually you'd consume more gas in neutral than if you were in gear...

Really? How does that work?

Gizm0 · 08-07-2013, 03:17 PM

Quote:

Originally Posted by cuiter23

Really? How does that work?

If you're in neutral, your engine still needs just a little bit of gas to make the motor turn at idle speed. If you're in gear and foot off the gas, the fuel injectors will not spray any fuel at all in the cylinder since the kinetic energy resulting from the car going downhill is what is making your engine turn through the drive train...

FormerRotor · 08-07-2013, 03:20 PM

For the us 335diesel, the optimum seems to be at just about 74-76mph, but obviously its a diff engine with a diff Trans and diff final drive.

I sometimes allow the car to gain momentum downhill and loose a bit toward to top of the uphills (as a semi driver would); this delivers crazy results. I can get around 47mpg on long highway drives like this if its clear sailing and I don't get distracted by my heavy foot.

Gizm0 · 08-07-2013, 03:23 PM

Quote:

Originally Posted by FormerRotor

For the us 335diesel (...) I can get around 45+mpg on long highway drives

Jealous

08-07-2013, 12:25 PM	#1
Gizm0 Colonel 426 Rep 2,136 Posts Drives: 08 e92 335i 6mt Join Date: Jan 2013 Location: Virginia iTrader: (1)	Gas mileage vs. speed Does anyone know if and where I can find such a curve for our cars? Especially interested in the e92 335i 6MT... Some cars are more fuel efficient going 40mph, others get better gas mileage going 65mph, and I just want to know where the "sweet spot" is on our cars. See below an example I did quickly to show what I'm after. __________________ JB4 G5 w/ Backend flash - Walbro 450lpfp - VRSF DPs - VRSF 5" stepped IC - DCI - ER CP w/ Tial BOV - 335is clutch
	Appreciate 0 Tweet Quote

08-07-2013, 12:35 PM	#2
wwc310 First Lieutenant 52 Rep 393 Posts Drives: e92 LCI 335i Join Date: Nov 2012 Location: Miami iTrader: (1)	im curious as well. I was under the impression that RPMs and gas mileage would show a better comparison __________________ 2011 335i e92 JB4 Stage 2, VRSF chargepipe, VRSF downpipe, Hankook Ventus V12 evo2s
	Appreciate 0 Quote

08-07-2013, 12:50 PM	#4
Gizm0 Colonel 426 Rep 2,136 Posts Drives: 08 e92 335i 6mt Join Date: Jan 2013 Location: Virginia iTrader: (1)	It would be a really simple exercise to do. Just find a flat road, cruise at different speeds, use the instant MPG on the dash and record a bunch of data points and then make a curve with Excel. I'd do it if I could, unfortunately there are no flat roads where I live... But if someone in here who lives in the flat lands feels bored... I did however notice on a road trip down to GA that my car seems to achieve better gas mileage around 70mph than 60mph... Last edited by Gizm0; 08-07-2013 at 01:10 PM..
	Appreciate 0 Quote

08-07-2013, 01:03 PM	#5
24601 Major 95 Rep 1,318 Posts Drives: Toy Join Date: Oct 2009 Location: Oahu, Hawaii iTrader: (5) Garage List 2015 Subaru Outback [0.00] 2015 Toyota Tacoma [0.00] 2013 BMW M3 [10.00]	I'd like to see this too! Good question Gizm0. Oddly it seems I do best at 80. __________________ Sold - 2014 F01 750Li xDrive CBM M-Sport Sold - 2013 E92 M3 SS w/ ZCP l ZPP l 2MK l 6NR l 752 Sold - 2009 E92 335i LMB M-Sport Sold - 2003 E46 M3 LSB SMG
	Appreciate 0 Quote

08-07-2013, 01:59 PM	#7
bhmax16 Lieutenant 164 Rep 401 Posts Drives: '22 M4, '23 CX-50 Join Date: Jul 2011 Location: North Carolina iTrader: (0)	Too many other factors come into play. You may be able to get in the ballpark, but windows up vs. windows down, AC on vs. off, the outside ambient temperature, etc... will all affect the final result for the user.
	Appreciate 0 Quote

08-07-2013, 02:41 PM	#11
Snow King Second Lieutenant 18 Rep 270 Posts Drives: 2007 E93 335i Convertible Join Date: Sep 2010 Location: Los Angeles iTrader: (3)	I would think that the earliest speed you can shift into the last gear (with low RPMs) will get the best MPG. Unless you have an M3, the final drive is calibrated for high MPG (overdrive) rather than performance.
	Appreciate 0 Quote

08-07-2013, 02:55 PM	#14
wesyee New Member 3 Rep 22 Posts Drives: 2009 335i Sedan Join Date: Aug 2012 Location: United States iTrader: (0)	Estimates based on cruise control readings: 55-60 MPH - 40 MPG 65-70 MPH - 32 MPG 75-80 MPH - 29 MPG __________________
	Appreciate 0 Quote

08-07-2013, 02:57 PM	#15
cuiter23 Major 81 Rep 1,094 Posts Drives: 2023 G87 M2 6Spd Join Date: Jul 2012 Location: Canada iTrader: (1) Garage List 2007 BMW 328i [6.00]	coasting in neutral downhill __________________ [SOLD] 2007 E90 328i - Titanium Metallic l 19" VMR V710 l H&R Trak+ Spacers l M-Sport Rear Bumper l Mtech Rear Lip Spoiler l Hamann Front Lip l Eibach Sportline l AA N52 Signature Exhaust l OEM Blacklines l MTEC V3 AE l 6000K HID l Nokya 7000K Fogs l MTEC License Plate LED l Interior LED l 15% Tint l BlackVue DR380G-HD + PMP 2023 G87 M2 6Spd - HEA Package \| OEM M Performance Carbon Wing
	Appreciate 0 Quote

08-07-2013, 02:58 PM	#16
iBoost Retired e90post Member 135 Rep 3,038 Posts Drives: real slow Join Date: Nov 2009 Location: Las Vegas iTrader: (13)	If i cared about mpg, i would be in a Prius. jk interesting topic
	Appreciate 0 Quote

08-07-2013, 03:20 PM	#21
FormerRotor Lieutenant Colonel 96 Rep 1,592 Posts Drives: 2011 335d, M-Sport Join Date: Jan 2012 Location: MD iTrader: (5) Garage List 2011 BMW 335d [0.00] 2017 BMW X5 xdrive35d [0.00]	For the us 335diesel, the optimum seems to be at just about 74-76mph, but obviously its a diff engine with a diff Trans and diff final drive. I sometimes allow the car to gain momentum downhill and loose a bit toward to top of the uphills (as a semi driver would); this delivers crazy results. I can get around 47mpg on long highway drives like this if its clear sailing and I don't get distracted by my heavy foot. __________________ My Picture Threads (Oldest to Newest): 1 2 3 Join BMW CCA! (Use my link and I get credit )
	Appreciate 0 Quote