Hey all,
I was wondering if anyone has used the Xcal II to calibrate their speedos for use with 20" wheels. There is a function that allows one to calibrate but you have to know the ratio of rotations????

Any help would be appreciated. I have 285/30s in the rears

Jesse

 

26.7" diameter vs. stock of 27.25"

IDK about your tuner, but I'll part with that bit of info that I DO know.

 

I wonder if I even need to adjust it then?

 

your speedometer will read 75, actual speed 74

 

Rgr, so it will rack up miles faster as well right?

 

Find out the revs/mile on your rear tires from the manufacturer. Then add that number on your tuner under the corresponding setting.

 

http://www.discounttire.com/dtcs/infoTireMath.dos

778.15 revs per mile

 

Try this out you can fill it in w/ stock info (235/55-17 ) and cross ref it with any size.

http://www.miata.net/garage/tirecalc.html