I have an sct Bama tuner and I need to correct my speedo because of my increase in rim and tire size, the only problem is I don't know how to or way to change it to, my rim size is 20 and my tire size is 245/35zr20 95w, thanks guys

 

You can go to SCT Tuner website and view owners manuals for instructions. http://www.sctflash.com/PDF/sf3_quickstart_web.pdf I believe "adjust options" is where you need to set your wheel and axle parameters.

 

You set the rev's per mile, which is 20168 / wheel diameter. You can calculate the diameter based on aspect ratio, but that's not very accurate since the values vary by the manufacturer, it can be off by 3 or 4 mph. I lay a ruler on the top of the wheel and measure the true diameter and use that.