Right. If 0.5 mph is so valuable (which I believe), how do we explain the slow trucks? How do we fix the slow trucks?

IIRC, the difference in radius between fresh tires and those worn down to just before they need replacing, changes the actual speed at any given speedometer reading by about 2%.

C=πD and all that.

	▲	schiffern 2 hours ago \| parent [-]
		Makes sense. Nowadays you could apply a long-term trim using the GPS speed, including correcting for variations due to steering inputs and elevation. Mandatory for new trucks and grandfather old ones, like how most new vehicle standards are adopted.