Big mileage drop

[Shane1]

Hey all I have an 09 Camry LE 4 cylinder with 52k mile on it. I normaly average around 28mpg. In the last month I've seen the mileage gradualy drop to around 19 - 20mpg. The only parameter that has changed is a new set of tires up front, but the mileage didnt drop instantly after the tires were installed its slowly declined. I'm going to get a new air filter today just to eliminate that as the problem but the current filter only has about 20k on it. I know there are alot of things that can affect mileage but this thing has gotten 28 average since i brought it home a couple years ago.
Any help would be appreciated.
TIA

[molson.david]

check your calipers.
mayby one of them locked?
another thing-temperature:
I'm getting 23-25MPG city all year around. when summer hits TX, my MPG goes south to 20-21...

[Yuko]

How's the tire pressure? That can affect mpg if it's low.

[heartdisease]

Do you have any codes? Do you have a smartphone? Get the "Torque" app you can check all kinds of stuff- o2 sensor temps fuel signals, really neat stuff. I have an 09 with the i-4 also. My mileage is fairly consistent if my driving style is. Did you change your route? 20k on a filter is really quite a few even without any dust imho. I clean my K & N at about 10-15k myself. I agree the temps can really affect things, It has been hotter than blazes around here for at least a month straight.