I have a 2002 accord 4cyl. About 4 mos ago I put new tires on P205 (one size bigger) my mpg's dropped and I discovered they only put 28psi in so I aired to 34 and my mpg went back to normal 27.5. Then the weather changed and all of a sudden my mpg has dropped to 23--yikes! I checked and changed my air filter, tire pressure at 34, recent tune-up and timing belt changed. Could the change in tire size and winter fuel mixtures make that kind of difference in mgp?

 

I'm on the same situation here.... lol

I don't have that much time with my 98 accord ex 2.3 L I got it just before the winter started. I live in chicago IL and its pretty cold out here;I always get about 260 miles per tank!!! This sucks big time... I'm just waiting for the summer season to see how many MPG I really get. It is mostly street driving.

My original tire size is 195-65-15 but instead I bought some 205-60-15.

 

yeah your gonna lose some mpg. remember the diameter of the wheel is a bit smaller now, nothing significant though but, with the winter weather both play a factor on your gas.

 

winter = colder air = denser air = ecu sends more fuel to compensate for extra air = lower mpg

 

Exactly. Theoretically less of the gasoline ignites as well which means more added into the combustion chamber to produce the same amount of power. Just chemistry really. I've dropped from 34-35 to 30-31mpg in the last few months. Average temps been about 20F. Happens every year.

 

Thanks everyone for your replies. Just went on a 220 mile trip. The temps are moderating (48 degrees) and I hit 29.5 mpg. I guess it is just the cold weather and ethanol that has reduced my mpg's.

 

Two more things influence it...

Winter-blend gasoline (if they use it where you live) has less energy.

Your new tires are bigger (right?) so your car actually travels FARTHER than your odometer says.

 

Does ethanol really decrease MPG?

 

Of course it does, it has less energy content per unit volume.

 

wider and smaller in diameter