12-10-2025, 07:42 AM
i'm also trying to match the gps speed to my odo speed. For some reason, my car had a 21inch as default in the computer wehreas the tires under it are 255/40R19. The speed was off by approx.5km/h.
I've adjusted the tire size (255/40R19) and matching circumference (2156) but now it is even more off.
Using your input, i've calculated that the difference between your supposed circumference and the best fitting circumference is approx 6%.
I'm also going to decrease the tire size in the car's computer with 6% (from 2156 to 2028) to see if that makes an improvement.
I've adjusted the tire size (255/40R19) and matching circumference (2156) but now it is even more off.
Using your input, i've calculated that the difference between your supposed circumference and the best fitting circumference is approx 6%.
I'm also going to decrease the tire size in the car's computer with 6% (from 2156 to 2028) to see if that makes an improvement.