Low rolling resistance tires ?

Its possible, but I bet other factors are also helping.

Steer tires are responsible for ~15% (12/80) of RR when loaded and ~30% (12/40) of RR when empty.

To go from 7 to 7.2mpg is a ~3% improvement in mpg which would require a ~6% improvement in RR. If you are loaded 67% of the time and empty 33% of the time, your steers account for 20% of RR on average so to improve overall RR by 6% your new steers would have to be 30% better.

G399s have a 117RR which means your old tires would have to have a RR of 152+ which is possible, but awfully high for steers.

 

Man, that's a lot of math. LOL

 

Lol...that's what I thought to

 

I third that thought on math, dude most of been an enginneer in another life.

 

I'm not so good at math anymore. I don't even have to add up the 3 lines in my logbook anymore. Computer does that for me lol.

 

New tires are usually higher RR than worn out ones. A tire with 4/32nds tread is 6% better RR than a new one. That is if they are the same tire brand and model.