New tires (same size) Worse gas mileage??

[Raphael]

I just got some new tires: Cavalier Sport King A/T (LT 235/75/15) aprox 29".

Replaceing my old Michellin LTX Mud and snow ( all season) of the same size. They were about 2/3 used.

My gas mileage went from 18.5 mpg to 16 mpg on the highway. This was consistent over 4 full tanks. I immediately felt as if the truck was a little slower to get movin after I installed the new tires. Maybe this was my imagination because they sounded and felt different. The sport kings have a much more agressive tread than the michellins. I did notice that my K&N was filthy and I'm cleaning it right now. Could a new tire cause such a decrease? Could a dirty air filter cause it either?

Thanks.

 

[Saleen_SR71]

tire pressure?

 

[Mbrooks420]

Tires vary in rolling resistance. 2.5 mpg is a bit unreasonable. For that much loss, it'd be worth buying new ones.

 

[aldive]

The more aggressive tread can and will usually cause a mileage drop. How much air are you running in them?

A dirty air intake will definitely reduce your mileage.

Did you change the tires in the winter? The winter gas can also cause a mileage decrease.

 

[Raphael]

Yes I did change them during the winter. When I drove from Saskatchewan to Vancouver, BC it was -3' Celcius. Then I bought the tires in Vancouver and drove back after a month. The temperature was now -28' Celcius. The highway mileage that I posted was from those two trips. One before the tire change and one after. I guess thats a pretty significant temp drop. Why is gas mileage worse in the winter? The PSI is 40 in each tire. The max is 50 psi cold. The tire shop told me to go with 40 all around.

 

[aldive]

Why is gas mileage worse in the winter?

It is due to the winter blend gas.

Take a look at http://slate.msn.com/id/2098672/

 

[spotted dogs]

the gas...

Based on my own experience I would agree about the gas being the main culprit ...once the cold hits the mileage goes noticebly down....the colder the worse off it gets. I was told the cold affects the gas combustion ( colder gas is harder to ignite than warm...kinda makes sense.) Apparently some companies are working on a pre heater for gas to make ignition more efficient, particlularly in cold climes.