I have the original factory tire size on my vx and with the tires at max sidewall pressure ( 51 psi ) my GPS and the odometer are within 1 mile of each other over 500 miles . Hope this helps
Thanks for the reply. I'm planning on getting the correct size tires when mine wear out but at the moment I just want to know if i'm getting more or less mpg with the 175/70/13 tires. I just want to know if my odometer is reading 100 miles, am i'm getting more or less mpg than the 100 miles. According to some of the replys here, it seems that with the 175/70/13 tires i'm actually getting more mpg than what my odometer is reading. So in this case if I get like 44 mpg than maybe in reality i should be getting like 45 mpg LOL. Well thanks for the reply.
Very helpful post since in my area as well is in another state 165 tires are no longer sold as 175 is smallest tire sold. Mileage traveled x0.025 + add difference to total mileage divide by mpgs burned/filled up at pump = total correct MPGs adjusted for tire size difference.