Decrease in MPG by 1 point... Tires to blame?

Yes it's the tires. I lost .5 to 1 mpg when I went to Yoko's from michillin XDN2.

 

Yes, you could check odometer VS GPS to see if odometer is off. Then just have a simple ecm change.

 

Also the circumference of the tire is different now. Not 12% different.

 

Thanks, Sir. Your input around here does not go unnoticed. Its OK to disagree with me and show me a thing or two as I dont know it all.

Everyone has their own preferences on tire pressures. I have never found an advantage to running tires lower than max spec tho anywhere between vehicle spec and tire max pressure rating is a good rule. I choose not to deflate a tire to enhance ride quality as I feel not worth the risk of any accelerated wear that might occur due to underinflation. Generally speaking I have always gotten longer life out of a hard tire.

 

I chock most of it up to deeper tread depth. You have much better grip now. More grip = more friction.

You'll need to average it out over a much longer duration. A good head or cross wind will wreck your mpg for the week.

A good set of tires with lots of bite is never a bad thing heading into winter.

 

Xdn2 is not the best tire for mpg as far as I know. What model Yoko's? They must be really bad then

 

I’ve never seen CARB or whoever check for tires if there’re compliant.

 

Don't forget that the truck stops are switching to winter blend fuels right now, and it typically reduces fuel economy 1 or 2 mpg.