I recently installed Stillen exhaust and upgraded to 20" rims. I noticed that my MPG gauge is a LOT lower than normal of my daily driving. I used to get around 20-21mpg now I'm avg 15mpg. I haven't actually calculated it myself but just going on the gauge that came with the car.

Is that gauge not accurate anymore b/c of the increase in wheel size or is my MPG really that bad b/c of the exhaust/rims now?

 

There is no wai your getting that low. I say the gauge is wrong. Does your gas go down like its 15mpg

 

When you increased the size of the rim the tire sidewall should have gone down so the overall size of your wheels didn't change.

Most likely what is happening is the new wheels are heavier than the OEM ones. How many miles have you driven to get the gauge to show that?

There are so many factors that play into MPG. could be a different gas station, different driving habits, or even if you are doing several very short trips, that will really kill your MPG

 

Off topic but Highspeed...I just got back from SC...since when did all SC gas stations start posting up one gas price but at the pump they're all a few cents HIGHER! Isn't that false advertising?

 

Hmmm I haven't noticed that. I will look next time i fill up...

But about your original post, I have noticed that different stations will result in different MPG's, I think because they use different additives.

 

Hmmm... so how is the sound at WOT? Hearing it more nowadays?
A small price to pay.

 

Figure your mileage the old fashioned way, divide actual miles traveled by actual gallons used. That is the only certain way to know your exact mileage, the computer is a little off for a variety of reasons. Mostly because it doesn't use an accurate amount of fuel in the calculation. That's why the gas gauge and distance to empty isn't really completely correct.

Fill up your tank. All the way. Reset your trip odometer. Drive until your next fill up. Fill up all the way again so you know you have a completely full tank. Note exactly how many gallons this takes. Divide the number of miles you've traveled by how many gallons of fuel it took to refill your tank completely. This is your accurate MPG number.

 

Yeah...haven't gone a full tank yet since the additions so I havne't had a chance to calculate...just wanted to know if anyone else had this issue.

 

I've been getting horrible mileage lately. Around 18 mpg. It has been 70% city driving 30% highway miles. I am thinking it is because it has been really hot and the engine isn't making as much power. I get on it once in awhile but I don't feel like i'm driving the car particularly hard.

 

Rims and exhaust shouldn't cause a 5mpg drop unless there have been drastic changes in your driving habits. Go with what BB said and see what results you get.

 

I thought about that too...but I honestly change gears around 3K rpms...

 

i have 20 inch rims intakes and full exhaust with high flow cars i am doing between 13-15 mpg. if i drive normal i might get 16-18

 

Just went on a road trip and reset the MPG gauge...got 26mpg...back to normal again...score!