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


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