gettung horrible mpg
10-01-2009, 08:06 AM
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gettung horrible mpg
The last two days going to work I have been getting the worst mpg I have ever had. I travel about 140 miles round trip and have used 3/4 of a tank both days. I only have intake and exhaust right now, and those have been on a while. The only recent things I've done is put my 18s and lowering springs on. The car seems to be running the same doesn't seem to run any different. Just wondering if anyone has any insight before I take to the dealership?
10-01-2009, 12:36 PM
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My mileage went down when I put my 18's on. I think it might be because the drive axels they put in the 2.2L equipped cobalt's arnt geared to deal with the extra rotational mass when you up-size to 18s.
10-01-2009, 12:56 PM
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I put my cruise on 70mph going to work, the wheels aren't a lot heavier. But that's what I thought too since I happened right after that. Guess I'll have to change wheel sizes. 
just got new tires 2 days ago too.
just got new tires 2 days ago too.
10-01-2009, 01:00 PM
#9
how heavy are the wheels? adding extra rotational mass will no doubt not only make the car slower, but affect mpg's. Auto or manual car? What's your mpg? What is your driving style?
10-01-2009, 01:07 PM
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What pressure are you running in those new tires? What size tires, compared to stock? These factor into rolling resistance, and if you say stepped up from 195/70-R15 to 215/45-R18, there's quite a bit more rubber on the road. Try bumping tire pressures up a couple pounds.
10-01-2009, 04:36 PM
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10-01-2009, 04:46 PM
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I believe they said the wheels weigh 22lb each, my car is an Auto. At 70mph I was averaging 32mpg before wheels, now I am down to about 26-27mpg. I don't drive hard, I have a straight shot to work no lights and one stop sign. Those are some heavy wheels, maybe that is the problem?
10-01-2009, 05:05 PM
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big ass heavy wheels will usually affect mpg. and having an auto doesn't help. trust me i know. but how bad of an mpg are we talking.
i got an average of 26mpg auto.
i got an average of 26mpg auto.
10-01-2009, 05:10 PM
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That's quite likely your issue. As I (and several others) asked earlier...tire pressures?
I'd probably recommend 32-35 psi, 37 tops - measured when they're at their COLDEST (i.e. first thing in the morning).
I'd probably recommend 32-35 psi, 37 tops - measured when they're at their COLDEST (i.e. first thing in the morning).
10-01-2009, 05:40 PM
#18
intake will increase mpg's provided your driving the same.
heavier wheels will decrease mpg's because you're using more energy to move the car.
4 speed auto's will not get as good gas mileage as the 5 speed manuals.
heavier wheels will decrease mpg's because you're using more energy to move the car.
4 speed auto's will not get as good gas mileage as the 5 speed manuals.
10-01-2009, 05:42 PM
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dude w/ my 18' on... (VERY HEAVY... over 20 lbs each...) I still got over 34 mpg on the freeway (before tuning) after tuning I'm getting about (38-40 mpg) and I'm an auto w/ full bolt-on's...
sounds fishy... ONLY 140 miles for 3/4 of a tank... doubt it's just the rims/tires...
sounds fishy... ONLY 140 miles for 3/4 of a tank... doubt it's just the rims/tires...
10-01-2009, 07:51 PM
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My tire pressure is 33psi each wheel. I figured I would lose maybe 1-2 mpg with the wheels not 5-6 mpg Oh well, I might think about dropping down to a 15 or 16 inch wheel with a smaller tire then. Thanks for the input guys.
Oh well, I might think about dropping down to a 15 or 16 inch wheel with a smaller tire then. Thanks for the input guys.
10-01-2009, 11:21 PM
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I have an automatic and have been having my MPG go up ever since I changed my air filter.
I was always looming around 29MPG before then I hit 30MPG last week.
Now I currently hit 31.3MPG today and it keeps going up .1MPG per day, not sure when it will settle out.
It is 60% inner city 40% freeway miles that I am doing.
Tires are stock steely 15s and filled to 30psi.
Mileage 35k...
I too am betting the huge wheels done your mileage in.
Did you reset the computer when you installed the wheels? The transmission might not have optimal shift points right now and is still running a program that your wheels are stock.
I also hear that Chevy can reprogram your computer for 17s, not sure about 18s though.
I was always looming around 29MPG before then I hit 30MPG last week.
Now I currently hit 31.3MPG today and it keeps going up .1MPG per day, not sure when it will settle out.
It is 60% inner city 40% freeway miles that I am doing.
Tires are stock steely 15s and filled to 30psi.
Mileage 35k...
I too am betting the huge wheels done your mileage in.
Did you reset the computer when you installed the wheels? The transmission might not have optimal shift points right now and is still running a program that your wheels are stock.
I also hear that Chevy can reprogram your computer for 17s, not sure about 18s though.
10-02-2009, 12:06 AM
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I was wondering if something with the ECU could be changed to accommodate for the 18s. Maybe GM or when I get tuned? Tomorrow when I get home I am going to switch back to my steelies and see if it goes back to my original mpg. We'll see from there.
10-02-2009, 12:18 AM
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I know the dealership can reprogram the computer to accept larger wheels.
I asked them if I got 16s put on my car if they could accomodate, and they said it is an easy reflash. They went on to say they can do this for 17s.
I did not ask about 18s but I can imagine they can do it.
Resetting the computer is just disconnecting the battery for a few minutes then replugging the battery. You then start the engine, let it idle for 5 minutes without ever touching the gas or putting it into gear. Then shut the engine off and restart.
The ride after this has set the new idle point, and will find the optimal shift points.
This will help, but a reflash is more what you need. Going from 15s to 18s is going to make the computer take a while to sort out. Such parameter changes as larger wheels will never be optimal running the standard program Resetting is quicker, has been so every time for me on every mod I have done one every car I have modded, although I acknowledge that just driving around it will also over time compensate. But again, not as good as the reflash. The dealer charges $110 to do it.
It takes several drives to settle into a program as the computer is doing a lot of averaging and testing to see what the sensors are telling the computer setting wise is optimal.
I asked them if I got 16s put on my car if they could accomodate, and they said it is an easy reflash. They went on to say they can do this for 17s.
I did not ask about 18s but I can imagine they can do it.
Resetting the computer is just disconnecting the battery for a few minutes then replugging the battery. You then start the engine, let it idle for 5 minutes without ever touching the gas or putting it into gear. Then shut the engine off and restart.
The ride after this has set the new idle point, and will find the optimal shift points.
This will help, but a reflash is more what you need. Going from 15s to 18s is going to make the computer take a while to sort out. Such parameter changes as larger wheels will never be optimal running the standard program Resetting is quicker, has been so every time for me on every mod I have done one every car I have modded, although I acknowledge that just driving around it will also over time compensate. But again, not as good as the reflash. The dealer charges $110 to do it.
It takes several drives to settle into a program as the computer is doing a lot of averaging and testing to see what the sensors are telling the computer setting wise is optimal.
10-02-2009, 09:42 AM
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Yeah I am going to go talk to my GM shop today about reflashing. On the drive to work today the rpms and shift points do feel a little different, my rpms are a lot lower in 4th gear then they used to be. I'll get there advice before I do anything. Just a question should I remove my K&N SRI and put the stock airbox back on, or will they trip on it for just doing the reflash?