Trust the ECU, the RPM is detremined by the engine the wheels and tires have nothing to do with it. The error comes in when the signal must be converted to a gauge needle position for the tach display.
There is no accuracy expectation on the stock tach, they are usually within +- 200 RPM. When I spin out to ~8K on the tach datalogs usually show ~7800. so mine reads a little high, but who cares.