According to mfr specs and DOT regs a speedo error range must be +2.5/-0, so all speedos read fast when delivered.
They all read fast but you need to site a source or I'm going to disagree.
https://www.fmcsa.dot.gov/regulations/t ... ion/393.82 says "Each bus, truck, and truck-tractor must be equipped with a speedometer indicating vehicle speed in miles per hour and/or kilometers per hour. The speedometer must be accurate to within plus or minus 8 km/hr (5 mph) at a speed of 80 km/hr (50 mph)." which is +10%/-10%
http://standards.sae.org/j1226_201108/ SAE J1226 "To begin with, manufacturers are afforded the latitude to aim for within plus-or-minus two percent of absolute accuracy or to introduce bias to read high on a sliding scale of from minus-one to plus-three percent at low speeds to zero to plus-four percent above 55 mph. And those percentages are not of actual speed but rather a percentage of the total speed range indicated on the dial. So the four-percent allowable range on an 85-mph speedometer is 3.4 mph, and the acceptable range on a 150-mph speedometer is 6.0 mph."
http://www.unece.org/fileadmin/DAM/tran ... 039r1e.pdf UN ECE Regulation 39 says : "no speedometer can read slower than the actual speed. Ever. On the high side, it’s allowed to read up to 10% above the actual speed plus four or six kilometers per hour, depending on the type of vehicle." So this one can be 0%/+10%.
And since the manufacturers don't like to do much customization per market they often just let them ride in the +3% to +8% zone for so they have plenty of margin for error.
So yeah I'll go with "all speedos read fast when delivered" but I don't agree with your +/-.