[kd5bjo]

That assumes there's insignificant slippage between the wheel and ground. A reasonable assumption for a rubber tire on a concrete road, with a 20 sq. in. contact patch. Less reasonable for steel on steel with a 2 sq. in. contact patch.

[rphlx]

I certainly agree that there are still errors, wheel slip being a major one. However, that does not cause an accumulating/ever-compounding error in speed nor distance travelled in the way that, say, a one-time error from an IMU's accelerometer does.

The lack-of-integration common in wheeled ground vehicles is highly beneficial to long-term speed & distance accuracy; it's a main reason why odometers were accurate for literally thousands of years prior to anyone knowing how to build an equally-accurate aircraft/spacecraft IMU. (The Romans were able to achieve <0.5% errors over hundreds of miles by the first century AD, something that no aircraft IMU was consistently able to achieve until after WWII).