Hello, I have a 2005 4cyl coupe 5 speed manual ,can someone help with MPG problem u just switched from the factory OEM 16x6.5 inch alloys to enkei falcon 17x7 21lbs wheels .i installed goodyear assurance tripletread 215/50/17 93V as i drive on snow a lot and i just recorded the worst MPG ever 25mpg and a few 27mpg on a 1200 miles trip .the tires are brand new and in comparison with the same goodyear tripletread but H rated on the 16 inch wheels 205/60/16 i did 33-35 mpg .also my winter general arctic on the 16 wheels are again 35mpg .that is almost 20-25% is that normal.

 

Nope, not normal. I'm thinking either your tire pressure is way low with the new tires or something else is an issue. If you still have the 16" setup, you might want to remount the wheels and see if it make a difference (I doubt it will).

 

i check my fuel mpg every time i fuel .with the winter tires on 16 inch wheels it gave me 33-35 on a 400 mile trip they are general arctic 23lbs according to tirerack .then i installed the new ones and did 1200 mile trip and fuel mpg went down to 25-27max.i was thinking to check my air filter but i cleaned it 4000 miles ago it is K&N.

 

forgot about the tire preassure but i do 34 psi and check it every time before trip

 

Even if your air filter was completely clogged it wouldn't reduce your fuel economy; modern engines measure the weight of the intake charge after it passes both the filter and the throttle body (the single largest source of intake restriction), and only then does it calculate how much fuel to add to the intake mixture. Said another way, the air to fuel ratio will remain constant.

The above said, do you have an oiled air filter? If so, then did you per chance over-oil it? This can often happen and the excess oil has a tendence to muck up the sensors which can then misread the weight of the intake charge and add too much fuel.

 

i did oil it in october 2012 .i am thinking may be just the tires are too heavy at 26lbs and with the new size 215(old 205) there is 10mm more surface and that makes for the low mpg.this upgrade should not make a big difference as it is very close to the original diameter and i am keeping almost the same weight but there is huge difference .i will see if it changes after the tires break in.i had between 36 and 40 mpg with the original bridgestone potenza tires which were really bad for wet snow but very good for mpg.
thanks a lot i will check again and see if there is any improvement.

 

The wheel and tire size change will ever so slightly affect the fuel economy to a negative degree for a couple of reasons:

• The wider section width is a very minor issue which probably wouldn't amount to even a quarter of a mile per gallon.
• Regarding the weight, even if the new wheel and tire combo is lighter, it will negatively affect the fuel economy due to the increase in rotational mass (also known as angular kinetic energy) due to the larger diameter of the wheel, specifically the diameter of the physical rim. Once again, even a loss of quarter of a mile per gallon would be a stretch.

Long story short, your fuel economy loss cannot be explained by the tire change.