Recalibration speedo
 

I am increasing tire size and would like to know if I buy a sct x4 with custom tunes will they have to include my tire revs in the custom tunes or do I change it myself with the sct? Last tune I had was a chip on my 2002 powerstroke which was idiot proof. Thanks for any info.

You can tell them to program a certain tire size for you and you can go in and adjust the tire size yourself at anytime.