BFG K02 off by 1 MPH?

[KahneFan]

I have an Escort Passport 9500ix radar detector which shows my speed as I drive. It has always been 100% match. However, since I got the BFG K02s, it is off by exactly 1 MPH slower than my dash. My dash says 65, the RD says 64. Lower speeds 35> I can get it to line up sometimes, but higher speeds are always off by 1 MPH. Haven't pushed it past 95 MPH to see if I can get a 2 MPH difference yet

 

[Stangshcky12]

Most speedometers are usually off from the factory. This is why most vehicles dont have digital speedometers (0 calibration)

Your tires must be a little bit smaller (~ 0.5") than the factory tires (even though the theoretical size is the same) which causes the speedometer to be off by a certain percentage. This is why it isnt noticeable at lower speeds. 1 mph is about 2.5% so when your speedo would say 90 your RD will read about 88 mph.