Don't trust the calulator. My 255/60r15 is supposed to be nearly 27" inches tall. Okay I calibrate my speed with that info and crap the RPM don't match. WTF?? Take a measuring tape and measure. OHHHHH 26.1" tall? Okay recalibrate speed for the correct tire size and it dead on for RPMs and MPH. The calulator converts the ratio but manufactures actually make tires different sizes. Even the tire manugacturer has the incorrect size on thier website.
