ericgray1

So I bought a 2009 Honda Civic DX with auto transmission, with 62k on it. I have been driving it for about 2 months now. I changed the oil in it (the old oil showed no signs of issues, basically normal). I changed the spark plugs to the Bosch Platinum 4 (just because I like to know everything is in good shape). Changed the air filter (old air filter was actually clean, but I did change it with FRAM anyways).

Anyhow the engine runs great. No noises. No leaks anywhere. No issues that I can see. Its super clean. The check engine light is not on. It idles like it should.

Now, I drive about 120 miles round trip to work a day. 60 miles in one direction and that is basically all interstate driving and I drive at 70mph with the cruise control set.

A couple of things to note: I pulled the hubcap steelies off of it and put some 17" wheels on it that I had on a previous vehicle with brand new 225/45/17 tires, The 17s felt lighter than the steelies.

Now I am big into monitoring fuel mileage. Right now I am averaging 30-33 mpg and even less with city driving. I am getting about 330 miles out of a tank and it religiously only holds approximately 11 gallons when I fill it up when it gets to empty. I was expecting this thing to get 38+ mpg. What is the deal? My mother in law's v6 accord gets better gas mileage than I do. I had an 04 honda civic that was getting 38+ mpg as well.

GolNat

iTrader: (7)

What kind of tires are the 17's? Are they at the proper PSI?

Also I would get NGK plugs, much better than Bosch.

ericgray1

Its just a generic tire that a local shop had in stock. The tire pressure is right. The pressure indicator is not illuminated. (I had the sensors swapped form the old tires to the wheels). I refuse to think that different name brand tires can cause a 8-10 mpg difference in fuel mileage. The rims are Tenzo R and were definitely lighter than the steel wheels that were originally on it.

ezone

You refuse to think that, why?
You'd be surprised at how much a set of wheels and tires can affect gas mileage.
Round and black does not make all tires the same.

Put the stock steels back on with the hubcaps and see what your mileage does.

I'm on 225/40/18s, I lost 15-20% gas mileage when I switched off the original equipment high efficiency, low rolling resistance Firetires. I even keep the pressures quite high.

Your best gas mileage will probably be in the 50-55 MPH range.

A dirty air filter has zero effect on gas mileage. Read that again if you need to.

Get the correct NGK Iridium plugs, they should last 100,000 miles or more. IZFR6K-11S is the plug type.
Hell, put the originals back in for that matter. Run them another 40k with zero problems.

Throw away the Bosch plugs before they cause you problems. I suppose you will refuse to believe they cause problems too?

I can RAPIDLY install a full set of Bosch spark plugs into the dumpster from 50 paces with one of these:










Check these sites out

http://www.hypermiling.com/

http://ecomodder.com/forum/EM-hyperm...ecodriving.php

GolNat

iTrader: (7)

Mad Skills

ericgray1

I read that the bosch spark plugs can cause performance issues, so thats why I mentioned that I changed to them. I planned on swapping them back out.

As far as wheel and tire. Over all its the same circumference and diameter as my previous steel wheel and tire set up as well as what im sure is lighter weight. The whole reason I got new tires was because the other ones were shot. So I can not put my old steelies back on it because those tires are gone.

Now do I think a tire can affect fuel mileage? Of course. Perhaps when its smaller or larger than factory specifications. Perhaps wider or narrower. Using a larger/heavier wheel tire combination. Wrong PSI. So on and so forth. But when you keep everything within specified range, even considering the generic value of a tire, the percentage in fuel mileage that is lost should be minimal, not 8-10 miles per gallon. That would be saying that a generic tire alone can equate to roughly 25% loss in fuel mileage when a car is rated to get 40mpg. I just can not see that as being the case considering the multitude of vehicles (60+) I have owned over the years and tires that I have gone through. This would be a first for me, even with the 5 honda's i have owned, that running a generic tire caused 25% fuel loss. My VW Jetta TDI that was fetching me 50mpg (with these very wheels, bad tires, and considering the overall measurements were not in spec with factory wheels) only caused me to get 48 mpg. 50 to 48. Thats acceptable.

ericgray1

I had my VW jetta that I sold to my dad because he needed a fuel friendly car. It was 2003. I wanted something newer and I knew honda civics got good fuel mileage and were practical. I bought this 2009 civic just before I had to go to atlanta GA for training for work which is about 450 miles from where I live. This was about a month ago. Anyhow I set the cruise control on the way there and got exactly 30 mpg. On the way back, since it was thanksgiving eve and I wanted to get home to family, i was cruising around 86 mph (sometimes even 90 mph) and believe it or not.. i average 34 mpg??

ezone

High performance tires, and lower quality tires can cause a significant difference in mileage, even if all else is the same. Sticky fat tires are not normally economy friendly. Check out some of the hybrid and hypermiler forums where they hash over tires all the time.

Tires alone may not explain all of your apparent mileage loss, but combine some other factors and they may total up to your loss.


Do you even have any idea what sort of consistent gas mileage your car was getting BEFORE you swapped tires? If not, then you really have no true baseline for comparison.

The big wheels are less aerodynamic, they catch a lot of air.

Low quality fuel can rob you of gas mileage.
Also, it's winter. Oxygenated fuel blended for colder weather kills some of your gas mileage (this is nationwide, no matter what your weather is like).
Ethanol lowers gas mileage, and it's nearly impossible to find 100% gasoline here in my area.
Top Tier Gas is recommended by Honda, and others: http://www.toptiergas.com/retailers.html

Is it cold there? Mileage drop.

Then there are things like the condition of the car itself, your driving habits, etc.



The EPA site says an 09 Civic 1.8 with an automatic trans had a window sticker that said 25/36 MPG (29 combined), and "your actual mileage and costs will vary". (Manual trans- 34 MPG)
You really might not be as far off as you thought.

I know if I run that far above the speed limit here, I'm not gonna do it naked. I'm gonna be in a line of cars where everyone is going that fast, and that gives me a bit of aerodynamic advantage.


My car is EPA rated at 28/39.
With the OE tires, I could exceed those numbers if I drove it JUST right (but I could never reach the rated highway mileage at real highway speeds!)
With the 18s I have on it now, I can't even get close to those mileage figures. Cold weather makes it worse.
If I flog it at all, mileage goes to downright crappy.

ezone

FYI, I just made a trip for Xmas, about 130 miles each way.

At 80 MPH with no wind block, I was showing 31.0 MPG steady on my IMID display.