hey guys,
I recently did some work on my 2000 max (fed). I installed the WS y-pipe, magnaflow cat, and aftermarket custom cat back. I also replaced the two front 02 sensors since i was getting the SES ( and i had already replaced the rear one prior. i figure i'd make everything new again). And i got g35 18 inch wheels, not sure if that would efffect anything..Anyway, i noticed my my mpg is pretty ****ty. Before, when i fill the tank up all the way, it would take about 50+ miles for the meter to reach the FULL mark, but now after 34 miles, it's a little past that mark. I use premium fuel, and at times when i come to a complete stop, i can smell a slight rubber burning smell..not sure if that accounts for anything, but i thought i'd include that in case...I notice that my rear 02 sensor is not "in all the way" as pointed out by the meineke guy, could that effect anything? So i have almost no freaking idea whats going on. Any help would be sooooo greatly appreciated!

-khanh

 

That will affect it to a certain point. Since you have a GXE, you had 16's, and you went to 18's, so yes, that may be some cause of it.

But I wouldn't make assumptions until I have actual MPG #'s.

 

Definitely., wait out the whole tank and take it from there. There are times when same thing happens to me. But towards the end of the tank everything evens out and I am at normal mpg. Between 20-23mpg.

 

hey thanks for the replies guys.
can 18's be such a gr8 impact? because i'm not a really aggrssive driver, i usually shift at 3k rpm or a little over. what should i check for in this case? i was thinking it'll be the 02 sensor thats not in all the way, and is prolbably not "Sensing" all the flow and in turn would make the car thinkthat its running too lean. that in effect would make it pump more fuel?
or maybe its somethign else. one more thing, lately i can hear the clutch attaching itself to the engine at low gears... but yea ill wait it out and see what happens.

 

I usually get 17-18 in the city if that helps you at all. I would deffintly check the o2 sensor though that can affect mpg.

 

i say its probably the wheels.. i put 20's on my i30, now my gas mileage sucks... it looks good though

 

what was the old and new tire size? If it is a large difference the circumferential length of the tire may account for the apparent difference. Also, the computer needs to readjust itself to the new O2 sensors. like others said, wait until you have full results. FOr some reason lately my gauge seems to be falling faster, but at the pump its all good, the light is just coming on earlier.

 

the rim size wont make a difference. its the tire size itself that will.

Ex. 16 in rim tire is 225/50/16
18 in rim tire is 235/40/18

This would show a difference.

But :
Ex 16 in rim 225/50/16
18 in rim 225/50/18

tire diam is the same so no diff at all.

http://www.tirerack.com/tires/tirete....jsp?techid=46

 

You smell burning rubber? Are the tires rubbing causing both the smell and contributing to lower mpg maybe?

 

very good point skier. Khanh, what was the tire size of the original tires and what do you have on there now?

 

The lack of knowledge in this post hurts my head

 

yea my tires are def different from the old ones. i cant remeber exactly, but the front ones are either 235 or 245. the rear ones are the same but they are wider.

 

i just had an allignment, and its not as persistent much as it were before. On a rainy day/wet road the smell its not even there at all.

 

thanks everyone for your input. i'd have to check the tires, im not completely sure.
-khanh

 

Sorry other .org members don't measure up NmexMAX. Here is a place you may feel more at home...

http://www.mensa.org/

 

nmexmax,
Take a leap. Your 26 and prob have never even seen the inside of an engine or have even broke down the rubber off a rim. The rim size will NOT make a difference in tire RPM if the tire size is exactly the same. so lets see a:
Cylinder with an OD of 4 inches and inside diam of 3.5 vs.
a cylinder with a OD of 4 inches and inside diam od 3in

They both have the same OD so they will both roll at the same revolutions per minute at a given speed. The only variable is the weight the 4x3 has which may make it roll slightly quicker.

 

yes there is difference your overal diameter will increase about 2 inches, because the hight of the rubber itself will be the same but it will be on 2 inch bigger rims

 

really so was i on seeing things when on my 02 Celica when i had 16 inch rims and got 18s but kept the same tire specs 205/55/16 or 18.

why when they were side by side was ther not even 1/4 in of height difference. They were the same height and width. Except for the rim itself

 

the reason you have to go down aspect ratio when you get bigger wheels is to keep overal diameter relatively the same

 

The rim/wheel size still makes a difference that was my point.

In MPG,and accordance to this thread, yes it will.


Seems to me

 

Hey Jeff, No one is getting on you but you should understand, wait lemme put it in simple terms..

If a Maxima came with 16 inch rims n tires, then went to say 18 or 19 inch.. For the rotational value which I forgot the math computation, but whatever, It takes more power for the car to move, lets break it down Engine->Tranny->Torque Converter or Clutch-> then Tires(rims). So more power needs, more gas.. .02

Remember now you are putting the car out of spec.

 

i had on stock 16s and with 205/65/16. The new Infiniti wheels are 18s,with 235/45/18. Would this impact my mpg?

 

shouldn't, because the overal diameter was kept about the same, but because the tires are wider you may get lover mpg because of more resistance/friction

 

here is one example straight from tirerack


overal diameter changed .9' for 1' bigger rim with the same aspect ratio

 

yes weight, obviously will take more power to move an object. But inside diameter does not affect the mpg. Yes the rim is considered the inside diameter. Im not looking to start a fight. i know what i know. Ive worked on many many cars since i cant even remember. Everyone can believe who and what they beleive and we all have a good day. A head wind will make u use more gas as well as adding a sub box. im sure the temp of the gas in the tank makes a difference. Who knows

 

Take a look at this link and see for yourself.

http://www.miata.net/garage/tirecalc.html

 

i'm pretty sure an 18 inch rim weighs more than a 16 inch rim, and an 18 inch tires weighs more than a 16 inch tire. more weight equals less gas mileage.

 

that burning smell could be your clutch

 

OP: Check your air filter, vaccume leaks, possible leak in fuel tank or somethin? Wheels wont make that big of a difference, i went from 16 to 18 and no mpg change, in fact mpg got better, i got lighter wheels.

 

shogun,
yea i was kinda thinking the smell could be from the transmission area too. the thing is that the smell is only there for a little bit after i drive for a while and then slow down almost to a stop or a complete stop. Then it goes away...although i do see some kind of liquid (not alot) that is hanging around below the transmission. could be transmission fluid leak?

in response to chopstix, i have a berk intake which i installed a month ago with the apexi filter, and it worked fine. fuel tank wasnt leaking as i see no drippage when the car is on or off. as for vacuum leak, i'd haveto check that out.

one thing i forgot to mention, the cat back that i installed was too big and too loud for me so i had midas replace the muffler. I left the car @ the shop and at the end of the day i found out that put this pansy *** muffler on with one tiny outlet exhaust pipe,...like those u see in stock civics. anyway, they are giving me a dual outlet on monday to replace that piece of ****. u guys think that might be held account for my massive mpg loss?

 

im sure i said that. "yes weight, obviously will take more power to move an object. "


"Wheels wont make that big of a difference, i went from 16 to 18 and no mpg change, in fact mpg got better, i got lighter wheels."

all in all Chopstix said the same thing i said just better

 

Weight of tire/wheel > diameter in impacting your MPG.

Blah...blah...blah...on diamater talk.

 

18 inch alloy 225/45/18s > than 205/65/15s steel? just double checked my wheels and this is exactly the transition.

 

So by using this calculator you can see that you added .5 inches overall diameter.

http://www.miata.net/garage/tirecalc.html

 

this calculator proves what I've been saying from the beginning

 

Odd, I went to a slightly taller tire to GAIN milage. Since the engine will be at a slightly lower RPM to maintain a specific speed, you could potentially reduce fuel consumption. But we're talking going from a 225/50 to a 225/55 which is very minor and the rim weight was not a factor. I got 423 miles on my last tank and usually average 390 - 420 per tank. This is with at least 18-20 full throttle rips onto the highway.

I'm also glad to see the aspect ratio / rim size issue cleared up. The bad info being posted gave me a nice laugh...