ok my truck has p225/75r15 tires on it.i have a set of rims and tires,p 225/60r16,and i get better mileage with these,than the factory size.anybody have any ideas,why?shorter tires,and rides better too.

 

did you work in the percent of tire height decrease into your mpg calculation? If not, you should because your speedometer and odometer aren't going to be as accurate as they were with stock tires.

 

x2
Your speedometer and everything will be off with a different size.
With your new tires, which are about an inch and a half shorter, needs about 45 more revs per mile than the others.
Also, with the smaller tires, your Speedo will read 60 when you're actually doing a little over 56.

 

Smaller Tires weigh less as well

Yes, when odometer says you have gone 60 miles you have actually gone 56 miles

Say you put in 16gal of gas and odometer said you have traveled 288 miles
288 / 16 = 18mpg

But you have actually only traveled 270 miles
270 / 16 = 16.8MPG

So MPG hasn't really changed