There are several radar based speed displays around me that I've used to check my speedometer. Every one of them says I'm going around 7% slower than what my car is saying. (between 37 and 38mph when I'm reading 40mph)

I'm wondering a few things. Several people here have reported their hand calculations of mpg to be somewhat lower than the what was reported by the car. Could this be the culprit? Also would adjusting the speedometer be covered under my warranty?

 

Toyota, for various legal reasons in many countries makes sure their speedometers are calibrated to read about 3 miles per hour higher than the real speed at 60 MPH. If their speedometers were wrong in the other direction, they could be subject to huge fines.

The government nannies want to make drivers think they are going faster than they really are in order to keep people within speed limits. So they passed regulations severely penalizing any car makers whose speedometers made drivers think they were going slower than they really were. That is, if a speedometer said you were going 60MPH, but you were really going 63MPH, that car maker could be heavily fined.

So, all car makers err on the side of caution and overcompensate in the other direction so that they don't get fined by the big bad governments.

Here is a link from last year that spent 3 pages discussing the erroneous speedometers: https://www.greenhybrid.com/discuss/...o-error-10105/

P.S. Toyota will NOT adjust the speedometer if within that margin of error.

 

As you'll see from the attached pages ME-39to42.pdf from the TCH Repair Manual, the US speedometer's calibration, as has been mentioned, is deliberately designed so as not to under-read. As you'll see, the metric speedometer's calibration is significantly more accurate — mine reads within ~1% of my GPS. This is not something that is adjustable, since the speedometer is a digital ("stepper-motor") gauge, and merely displays the digital information sent to it by the ECU. [The fuel and temperature gauges are also digital. Only the FE meter is an analog instrument.]

Stan