Anytime! I always love a good debate or a good opportunity to learn something new.
I read that article but there’s three things that stood out to me.
1.) speedometer inaccuracy by law. Generally in the us your speedometer will read 2mph higher than your actual speed. That’s fairly universal. I’ll concede that tire inflation, size, and wear have some impact but I’d argue not to the extent they imply. You won’t suddenly have a 10mph difference from your true speed. Maybe 4-5 tops baring unusual circumstances including but not limited to failure of the sensors that pass data to the speedometer.
2.) gps inaccuracies. They do a great job pointing out more complex details such as satellite positions, number of satellites, and their poor understanding of turns. However I believe that can be compensated for with software assuming we have a fairly accurate measurement of distance driven and time it took as well as an accurate position thru the whole processes.
3.) they’re selling a product. I’m always skeptical of companies trying to down a tried and true method and push something new that is directly tied into their product.
All that being said, I’d still argue that gps is not a suitable replacement for the day to day speedometer readings.
1) speedometers are generally quite accurate. Like you said, the vendors have them set high (WTF!), but only typically by 1-2 miles max. I have routinely and repeatedly tested my speedometers on multiple vehicles (Volvo and GMC) for decades, and they have
always been quite close, absolutely close enough for driving speed limit issues.
2) GPS accuracy I have also tested. iPhone 13 Pro, iPhone 14 Pro, Apple Watch 7, Apple Watch Ultra. Accuracy is spectacular, to within a few feet on a 1/4 mile track even;
except when it is not. I walk the identical couple of miles every night and usually the distance repeats to within a few meters, but
sometimes it will be off by a lot, 50-500 feet.
No vehicle speedometer has ever done that in my testing, not once. If a speedometer is inaccurate it is by a consistent small repeatable amount.
Bottom line is we agree:
gps is not a suitable replacement for the day to day speedometer readings.
Edit: This is 2023 and CarPlay-type devices are now ubiquitous. As much as I hate adding laws to a world already overloaded with laws,
states and localities should be required to electronically promulgate geographically accurate speed limit info for Apple/Waze/Google whomever to access and link to their apps. If they fail to do so then they should not be allowed to generate revenue ticketing speed limit violations.
It ain't rocket science. This is old tech now and far overdue. We just have lazy law enforcement, happy to keep consumers confused and unintentionally stumbling into speed violations.