ktm670

Hi Guys. I recently brought my first non Ktm bike from the last 20 years and I like it very much so far ! This is a Tracer 900 Gt that was almost brand new with 3000km (1864mi) I did change the bad Oem Dunlop tire on it for the new Bridgestone Battlax T32 that complete change the bike agility. Last week i did a nice 1000mi trip on 36 hours so I use my GPS. I was choc to see how much off my speedo is. At 130 km/h (80.78 mi/h) on the speedometer I was at 120 km/h ( 74,57)on the gps witch make a 8,33% mismatch speed. That is by far the higher I did see. Of course I did use the same Tire size ( 180/55zr17 and 120/70Zr17) Did anyone know how to correct that ?