Gas Performance of AC vs Drag - Camaro5 Chevy Camaro Forum / Camaro ZL1, SS and V6 Forums

Jonster · 07-01-2013, 02:27 PM

I brought up in one of the gas mpg threads "Does running the AC affect my mpg?" and I decided to do some research. Of course the answer is yes, but what about windows down vs AC?

In today's world, the average (modern) car is fairly aerodynamic and getting better at gas usage. When it comes to deciding to roll the windows down or run the AC, it seems physics solves the issue (sort of). The general rule I found was that 52mph is the average speed where having the windows down will lower gas efficiency due to drag. Anything under 52mph with windows down allowed the car to utilize the gas more efficiently.

Now that was a GENERAL AVERAGE amongst standard cars. I know that our cars are probably more aerodynamic than most, but has anyone really had firsthand experience with this in the community?

I haven't had the luxury of a LONG ride yet, but I would love to see REAL LIFE inputs on performance difference.

Other interesting questions:
How does a convertible affect the aerodynamics of the car/gas efficiency (down and up)?
How does the convertible 2nd set of back windows (top up) affect the aerodynamics of the car/gas efficiency?

TLDR: Ride with your windows up and AC off and your car will be at max performance

Vroom_vroom · 07-01-2013, 02:42 PM

interesting. seems at 70+ i get a lot of air turbulence in side the car with them down. now you have me wondering.

fcatch76 · 07-01-2013, 02:56 PM

you will definately get better gas mileage with windows up and AC on over having windows down.

serialmike · 07-01-2013, 03:57 PM

Just drove mine from delaware to florida. 1600 miles on it to start, 2500 now. 1ls, ran as high as 30.1 ac off some traffic caused me to end with 29. When it got to hot went to ac and ran 28-28.5mpg. Range of speed was 60-77 ran 5 to 7 mph over speed limit all the way.

Jonster · 07-01-2013, 04:12 PM

Quote:

Originally Posted by serialmike

Just drove mine from delaware to florida. 1600 miles on it to start, 2500 now. 1ls, ran as high as 30.1 ac off some traffic caused me to end with 29. When it got to hot went to ac and ran 28-28.5mpg. Range of speed was 60-77 ran 5 to 7 mph over speed limit all the way.

when you say "ac off" were your windows down or up? It seems you were driving with the windows up the whole time, but if not maybe our cars are more aerodynamic than I thought with the windows down.

The Stig · 07-01-2013, 04:20 PM

Myth busters did an episode on this. I'm sure it's on the YouTube somewhere.

And windows down will increase the drag coefficient as air is being sucked into the cabin.

Beaver Creek · 07-01-2013, 04:23 PM

This will be interesting...

Our cars are narrower across the rear of the window opening, than across the front. That would lead me to believe that the windows down would not make much of a difference than up. On the Camaro anyway.

Hmm...

Lee

911medic · 07-01-2013, 04:30 PM

Quote:

Originally Posted by Jonster

TLDR: Ride with your windows up and AC off and your car will be at max performance

Ummm... Isn't this just common knowledge?

CWI · 07-01-2013, 04:44 PM

I thought modern AC and ventilation systems work in such a way that the compressor cycles on and off whether we are using AC or not. Even in the winter while we use the heat. Don't they cycle on/ off year around to keep them lubricated?

In which case, the drag on the engine would be the same either way.

jd10013 · 07-01-2013, 05:18 PM

Quote:

Originally Posted by The Stig

Myth busters did an episode on this. I'm sure it's on the YouTube somewhere.

And windows down will increase the drag coefficient as air is being sucked into the cabin.

yes, but that was only at speeds over 50. the first time they did it they kept the speed low, like 25 or something, so the tires wouldn't wear as bad. and that result showed no change in MPG. the second time they did it (because a lot of people wrote in making note of the speed) they ratcheted the speed up and it did in fact show a decrease in MPG with the windows down.

patternpilot · 07-01-2013, 05:54 PM

Back in the day when AC compressors were piston type you could really tell the difference in drag and mileage. Turn one of those baby's on and the car slowed down. With the new style rotary AC compressors they have much less drag. No mater how much it costs, I am keeping my AC on while I drive the car. I want to be comfortable. There's more to life than gas mileage.

Vroom_vroom · 07-01-2013, 06:02 PM

almost fell over when i saw the stig has "fireproof moderator"

Jonster · 07-02-2013, 07:40 AM

So I guess the only people who have knowledge/information about the aerodynamics of the car is GM. I guess we just have to trust that they are thinking of windows down drag.

I am still curious how much drag a convertible produces with the top up and down.

snymat68 · 07-02-2013, 08:45 AM

Quote:

Originally Posted by jd10013

yes, but that was only at speeds over 50. the first time they did it they kept the speed low, like 25 or something, so the tires wouldn't wear as bad. and that result showed no change in MPG. the second time they did it (because a lot of people wrote in making note of the speed) they ratcheted the speed up and it did in fact show a decrease in MPG with the windows down.

I think they concluded that below ~45mph it's better to keep windows down and ac off. Above 45 they said ac on and windows up is more efficient. But I think the results were so negligible it was easily within the statistical error margin, ie do what ever you want.

07-01-2013, 02:27 PM	#1
Jonster Drives: 18 2SS Vert Hotwheels Join Date: Sep 2012 Location: Maiden, NC Posts: 588 View My Garage	Gas Performance of AC vs Drag I brought up in one of the gas mpg threads "Does running the AC affect my mpg?" and I decided to do some research. Of course the answer is yes, but what about windows down vs AC? In today's world, the average (modern) car is fairly aerodynamic and getting better at gas usage. When it comes to deciding to roll the windows down or run the AC, it seems physics solves the issue (sort of). The general rule I found was that 52mph is the average speed where having the windows down will lower gas efficiency due to drag. Anything under 52mph with windows down allowed the car to utilize the gas more efficiently. Now that was a GENERAL AVERAGE amongst standard cars. I know that our cars are probably more aerodynamic than most, but has anyone really had firsthand experience with this in the community? I haven't had the luxury of a LONG ride yet, but I would love to see REAL LIFE inputs on performance difference. Other interesting questions: How does a convertible affect the aerodynamics of the car/gas efficiency (down and up)? How does the convertible 2nd set of back windows (top up) affect the aerodynamics of the car/gas efficiency? TLDR: Ride with your windows up and AC off and your car will be at max performance __________________ 2018 2SS hot wheels convertible

07-01-2013, 02:42 PM	#2
Vroom_vroom The gritos pollo!!! Drives: Like a idiot Join Date: Jul 2012 Location: Las Vegas Posts: 1,215 View My Garage	interesting. seems at 70+ i get a lot of air turbulence in side the car with them down. now you have me wondering. __________________ ______ If you don't stop how can they give you a ticket?-The Big Tuna___ '12 1Ls Camaro; Slp loud mouth I\|maganflow x-pipe\|Injen long ram intake\|brembo brake upgrade\| russell s.s. lines\|2LT polished 19's\|billet 5mm spacers\|tinted tail lights&markers\|pdmi\|billet c. can\| '13 Avenger R/T '77 T/A 6.6;, draining my wallet.

07-01-2013, 02:56 PM	#3
fcatch76 Drives: 2012 2LT RS Join Date: Mar 2012 Location: United States Posts: 63 View My Garage	you will definately get better gas mileage with windows up and AC on over having windows down. __________________ 2012 2LT/RS AGM- Injen CAI- MRT v2.0- Elite catch can- VMax PTB- ACS T5 splitter,rockers, rear panels and T2/s ports- Strut brace- Oracle side markers- JDP DRL Harness and ACS Eagle T2 leds-5% tint-Decepticon theme

07-01-2013, 03:57 PM	#4
serialmike Drives: Camaro 1ls Join Date: Apr 2013 Location: St Augustine FL Posts: 89	Just drove mine from delaware to florida. 1600 miles on it to start, 2500 now. 1ls, ran as high as 30.1 ac off some traffic caused me to end with 29. When it got to hot went to ac and ran 28-28.5mpg. Range of speed was 60-77 ran 5 to 7 mph over speed limit all the way. __________________

07-01-2013, 04:20 PM	#6
The Stig knows 2 facts about ducks Drives: ...and they're both wrong Join Date: Aug 2009 Location: The HMS Invincible Posts: 25,072 View My Garage	Myth busters did an episode on this. I'm sure it's on the YouTube somewhere. And windows down will increase the drag coefficient as air is being sucked into the cabin. __________________

07-01-2013, 04:23 PM	#7
Beaver Creek Drives: 2011 Camaro Synergy II Join Date: May 2013 Location: Madison, NC Posts: 57	This will be interesting... Our cars are narrower across the rear of the window opening, than across the front. That would lead me to believe that the windows down would not make much of a difference than up. On the Camaro anyway. Hmm... Lee

07-01-2013, 04:44 PM	#9
CWI Helping Build America Drives: 2010 2SS/RS,LS3 2013 Duramax 3500HD Join Date: Aug 2008 Location: Freeport LPG Export Posts: 3,839 View My Garage	I thought modern AC and ventilation systems work in such a way that the compressor cycles on and off whether we are using AC or not. Even in the winter while we use the heat. Don't they cycle on/ off year around to keep them lubricated? In which case, the drag on the engine would be the same either way. __________________ Life's journey is not to arrive at the grave safely in a well preserved body, but rather to skid in sideways, totally worn out, shouting "Holy shit, what a ride!"

07-01-2013, 05:54 PM	#11
patternpilot Drives: 2012 2SS/RS Join Date: Aug 2011 Location: Tri-Cities WA. Posts: 928 View My Garage	Back in the day when AC compressors were piston type you could really tell the difference in drag and mileage. Turn one of those baby's on and the car slowed down. With the new style rotary AC compressors they have much less drag. No mater how much it costs, I am keeping my AC on while I drive the car. I want to be comfortable. There's more to life than gas mileage. __________________ There's more to life than gas mileage LS3, Whipple, Custom Comp Cam, springs, pushrods, timing set, CAI intake, Apex cold air scoop, Doug Thorley TRI-Y headers, Billet Custom Products baffled Valve covers, Mighty Mouse Catch can, ADM FPCM, ZL1 fuel pump, MSD boost-a-pump, Hex Vent hood vents, ProSport gauges(fuel pressure, AFR, Boost), Corsa, 100 cell Cats. Jannetty remote tuned, Pfadt trailing arms, all parts user installed. No Dyno yet. Manual trans. 3.45 gears.

07-01-2013, 06:02 PM	#12
Vroom_vroom The gritos pollo!!! Drives: Like a idiot Join Date: Jul 2012 Location: Las Vegas Posts: 1,215 View My Garage	almost fell over when i saw the stig has "fireproof moderator" __________________ ______ If you don't stop how can they give you a ticket?-The Big Tuna___ '12 1Ls Camaro; Slp loud mouth I\|maganflow x-pipe\|Injen long ram intake\|brembo brake upgrade\| russell s.s. lines\|2LT polished 19's\|billet 5mm spacers\|tinted tail lights&markers\|pdmi\|billet c. can\| '13 Avenger R/T '77 T/A 6.6;, draining my wallet.

07-02-2013, 07:40 AM	#13
Jonster Drives: 18 2SS Vert Hotwheels Join Date: Sep 2012 Location: Maiden, NC Posts: 588 View My Garage	So I guess the only people who have knowledge/information about the aerodynamics of the car is GM. I guess we just have to trust that they are thinking of windows down drag. I am still curious how much drag a convertible produces with the top up and down. __________________ 2018 2SS hot wheels convertible