So I have been told by one or two Taiwanese colleagues that the scooter manufacturers (and maybe it extends to all automobiles) design the speedometer to make you think that you’re going faster than you actually are. For example: my speedometer measures 60 km/h but in fact I’m really only going 55. I just asked another coworker (difference city and office) and she told me that “everyone says that but no one is quite sure.” So I was wondering if anyone on this forum has definitive proof or at least anecdotal proof one way or another on this issue. Any insight is much appreciated!
A quick google will lead to many sources. It’s pretty standard for all auto manufacturers.
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If there’s some straight, relatively quiet road you take regularly, it should be trivial to estimate your actual speed (to within ±10%, say) based on the measured distance (e.g., Google Maps) and time taken.
I think some GPS systems can calculate it too, no?
Or revs and tire circumference (though the rev counter may not be accurate enough either).
Says that here too (for Australia):
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Actually there are some Apps that can help you check the speed , and you can enable the speedometer in Google Maps
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I have an app that helps me to see my speed by displaying it on my phone which is positioned higher than the bike speedo. The app also happens to warn about speeding cameras, but I only use it to make sure I am always under the legal limit.
The app speed is consistently above the bike, but not more than 5km/h.
Of course, the bike, the app, and the speed cameras each use a different method to establish speed. I’m not sure which is the most accurate
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Yeah, this is the app I use. Gives the same speed as Google Maps, probably because it is calculated the same way (or, possibly, taken from the exact same source)
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GPS will be the most accurate overall, as the mechanical methods are subject to physical variance in the moving parts (tires etc) and the speed cameras are out in all kinds of weather and don’t get recalibrated very often, (if ever).
Another option would be for the speed cameras to simply log your travel time between camera locations, but according to somebody from that dept I happened to chat with one day, they are not (yet) that sophisticated.
Phones don’t use real satellite GPS, it’s triangulation based on cell tower data. Might be affected by network connection and traffic, and the algorithm, no?
There are speed zones that do this in Taiwan
Don’t they have those places where it displays what speed you are going at based on their radar readings? Maybe drive past one of those and note the difference.
Remember these are mast produced units so there can be some veriation from manufacture, then there are other things that come into play, have you changed the tyre or over/ under inflated, where and tear on the mechanism over time etc, so manufacturers tend to caution on the safe side a little.
Gps receivers should also be calibrated regally for accuracy, they can also get less accurate in built up areas, cell phone can get less accurate in remoter areas.
I had the speed camera app on my phone, a dedicated GPS unit on my rider camera and the speedo on my motorcycle, I would regally get a 8kph difference doing around 40, speedo and GPS was close normaly around 3kph even at higher speed, phone could be around 5kph behind my speedo.
The phone was least consistent but for some reason I tend to use it the most as it’s easy to see and had the speed camera data and generally keeps me out of trouble.
There are a couple I go through regally but the speed camera app deals with them well, even given you a count down till you have cleared the zone.
We got the average speed cameras in the uk around 2000 I was working as motorcycle courier/delivery driver to pay for my education at that time, and I had to draw big red lines on my A to Z.
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Get your manservant to give it the once over 
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Phones do use real GPS, but one needs signal from at least 5 satellites to be very accurate and that can be difficult in a city.
Enter “enhanced” location service, which does add cell triangulation to the mix, as well as nearby “known” wifi APs.
If you wish to test the quantity and quality of GPS signals at any time you can use the very handy SatStat app:
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Cell phones are not satellite phones
GPS is a satellite-based spatial location system completely unrelated to the communications satellites used by “satellite phones”.
Please read up on how modern phones use GPS, I think you’ll find it enlightening.
(Or just load SatStat and go wander around outside for a few minutes.)
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I double checked before my last post.
Edit, oh, but didn’t use the right search terms. Today i learned
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I thought the more recent star link satellites are being equipped with ability to connect directly to a cell phone, at least for emergencies.
GPS is also just based on a satellite group run by the US. Today there are more providers for satellite based positioning.
GLONASS, BeiDou, Galileo, QZSS, NavIC to name a few.
Several of those predate GPS, actually.