Jim Haight wrote to All:   
      
    JH> So I was thinking about increasing the diameter of the tires on my   
    JH> 2012 Ford Escape. Stock is 135 x 70 x 16 and in the forums, people   
    JH> are going up to 145 x75x16 for an inch more height along with H&R   
    JH> lifting springs which give another inch.   
      
   The springs will have nothing to do with the tire diameter or your speedo   
   error.   
      
    JH>  In as much as the final drive ratio has changed then the speedometer   
    JH> is off.   
      
   135/70x16 = 23.44" x PI = 73.64" circumference = 860.4 rpm/mile   
   145/75x16 = 24.57" x PI = 77.19" "           " = 820.8 rpm/mile   
      
   Ford is capable of reprogramming your car with their scan tools. All they   
   do is re-enter the new tire diameter and you're all done.   
      
    JH> Someone said that nowadays, you can get software that will   
    JH> recalibrate the speedo as well as reprogram the power curve of the   
    JH> engine to accomodate the change in your tire diameter that would help   
    JH> with the slight decrease in gas mileage.   
      
   Decrease? A taller tire should give you a slight increase in mpg...   
      
    JH>   I have done performance flash before on a VW gti but never thought   
    JH> about how you can recalibrate the speedometer digitally.   
      
   If there is one available for your car. Most of the CPM programmers on the   
   market cater to 'performance' oriented cars. If they make one, you can buy   
   it from HypeTech and plug it into the Ford's underdash port and reprogram   
   some parts of your CPM...you can find them on the internet.   
      
   There is one that I use called HP Tuner. I have it installed on a laptop   
   computer. It has all of the bells and whistles to change the performance   
   aspects of your car (including tire diameters and air/fuel ratios). Dunno   
   if they have one for your Ford. Last I heard, their programmer and   
   software costs over $500...   
      
            R\%/itt   
      
      
   --- GoldED+/W32 1.1.5-31012   
   --- D'Bridge 3.92   
    * Origin: Bow Tie Racers, Been There, Done That! (1:387/22)