Quote:
Originally Posted by rich8566
Sorry, but I disagree with your statement that this is a mandate by the Feds.
I currently have two Hondas that have dead on accurate speedos. All of our prior Hondas had dead on accurate speedos. My 2000 SL5O0 has a dead on accurate speedo. Our Audi A4 has a dead on accurate speedo. Our 2014 Ford Escape has a dead on accurate speedo. Every BMW I've had (5 since 2007) were inaccurate to the tune of 3-5%, or 2-3 mph at normal road and highway speeds. .
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You're just flat wrong. Honda in particular has had a reputation for decades for providing readings that are higher than the actual speed.
I don't know how old you are, but I was alive in the 1970s and 1980s when this was an actual issue discussed not only in government but in Car and Driver and Road & Track, if my memory serves me correctly (I subscribed to both as early as 1980). Back then, many speedos were mechanical -- driven by a cable -- and could not be calibrated electronically in any way. You had to change physical gearing to change the calibration. To allow for the factors I mentioned earlier, manufacturers were compelled -- again, unofficially -- to calibrate speedos to read higher than the actual speed. Among gearheads and auto enthusiasts, this was an accepted thing.
Also consider that the average passenger car tire loses 1/2" in diameter as its tread wears. This converts to roughly 2 percent of its rolling circumference -- and with tires with deeper tread such as trucks, the difference is greater. Presto!: your speedometer is reading 2 percent faster with worn tires. This is a physical fact that no electronic calibration can correct, either.