I wonder what you mean by "accumulates". If I change the tires, the slight difference due to the previous brand and the slight difference due to the new brand d

I wonder what you mean by "accumulates". If I change the tires, the slight difference due to the previous brand and the slight difference due to the new brand do not compound. I only get the last one. And if the older ones were worn, the new ones will have less error, as they are less worn. If the errors really accumulated, once in a while we would need to recalibrate the speed sensor, else we would be doing 90 and showing 10. In fact the error is limited to some reasonable amount.