Hi (speedometer accuracy)

[Muffler]

When checking mine with stock 225/45R18’s at new against phone & TomTom satnav, Speedo was overstating GPS recorded speed very marginally. With the Vector 4S 245/45R18’s I’m now running its spot on, including against roadside speed boards and the new Dragy I received for Xmas (haven’t tried any launches yet - conditions are too damp…)

 

[decrep]

Any idea what the difference in circumference is?

Is the ratio between old and new circumference, the same as the ratio between old and new gps accuracy?

This could help in our discussion about the speedo being calibrated by the on board GPS.