[Palf70Step]

That tire size is around 1.5" shorter that stock, so you will be off by about 5MPH (faster than speedo says). Considering other factors of how far off they can be originally,plus did someone change the rear end gears or tranny will aslo add to the inaccuracy of the reading. To get it closer as uncle watts mentioned, you can change the gear on the speedo cable, but whoever does the calculations, to do it correct will need the color or gear on the tranny shaft, as well as what your rear end gear ratio is.