5 ms·

Very cool. For fun, I once verified the actual speed of a motorbike in a youtube video. The video was a first person POV which also showed the speedometer clo

by oxplot 7y ago

Very cool. For fun, I once verified the actual speed of a motorbike in a youtube video. The video was a first person POV which also showed the speedometer clocking at 300km/h on a German autobahn. There were various comments on the video claiming it was fake. So I decided to verify it myself. I went on Google satellite imagery and looked at a few autobahns to see how far apart the line markings were. I then measured how many lines the bike passed by going through the video frame by frame. Did the math and it turned out that the bike was actually moving at about 290 km/h. It was either measurement error on my part, measurement error on the bike's part, or that the bike's wheels were slipping at that speed (which was something I didn't know before this). I didn't look into it any further. It was a fun experience.

pintxo 7y ago
For the next time: the line markings "Leitlinie" on the Autobahn are 6m long and spaced 12 meters apart [1]. The poles to the side "Leitpfosten" are spaced 50m apart. And by law [2] all speedometers for ~German~ European cars + and bikes usually shows a too high speed: > The indicated speed must never be less than the actual speed, i.e. it should not be possible to inadvertently speed because of an incorrect speedometer reading. > The indicated speed must not be more than 110 percent of the true speed plus 4 km/h at specified test speeds. For example, at 80 km/h, the indicated speed must be no more than 92 km/h. [1] https://de.wikipedia.org/wiki/Stra%C3%9Fenmarkierung https://de.wikipedia.org/wiki/Stra%C3%9Fenmarkierung [2] https://en.wikipedia.org/wiki/Speedometer#International_agreements https://en.wikipedia.org/wiki/Speedometer#International_agre...
CraigJPerry 7y ago
IIRC there’s a script written in the RC model aircraft community that verifies claimed speed of models by assessing the doppler shift from the video sound track as the plane passes. /me googles https://youtu.be/DZZWtT32ymY https://youtu.be/DZZWtT32ymY
- kthejoker2 7y ago
  But to the point of faking it seems like it'd be even easier to generate a fake audio "shift" of your claimed speed.
Jamwinner 7y ago
Most motorbikes overstate speed for whatever reason. Usually by 2-5%. I would agine your estimate was more accurate. There is a whole industry for correcting motorcycle speedometers.
kart23 7y ago
Its speedo error. Most cars and motorbikes slightly overestimate speed, and the effect is more pronounced at higher speeds. This is just to be on the safe side with regards to speed, as tire tread, tire size, temperature, etc. can all have positive or negative effects on speed. Its usually around 5%. You can test this by driving at a constant speed near those radar speed detectors and observing the speed on the board vs. your speedometer. My speedometer is usually about 4 mph faster at 50 mph.
- akiselev 7y ago
  Note that those road side systems are usually only used as a road sign and the vast majority (at least in California) use a cheaper and less accurate/repeatable sensor than the ones used by police for speed infractions. This is especially pronounced on highways where the same sensor can give you several different readings at 1-10 mph less than actual speed.
  - kart23 7y ago
    Or use the gps speed from google maps. That should be pretty accurate.
EthanHeilman 7y ago
What if the video was just sped up? I guess you could use the speeds of the other vehicles as a reference point assuming they are going around the speed limit. It would be harder to show that the video wasn't sped up if there were no other vehicles on the road.

by oxplot 7y ago

pintxo 7y ago

For the next time: the line markings "Leitlinie" on the Autobahn are 6m long and spaced 12 meters apart [1]. The poles to the side "Leitpfosten" are spaced 50m apart. And by law [2] all speedometers for ~German~ European cars + and bikes usually shows a too high speed: > The indicated speed must never be less than the actual speed, i.e. it should not be possible to inadvertently speed because of an incorrect speedometer reading. > The indicated speed must not be more than 110 percent of the true speed plus 4 km/h at specified test speeds. For example, at 80 km/h, the indicated speed must be no more than 92 km/h. [1] https://de.wikipedia.org/wiki/Stra%C3%9Fenmarkierung https://de.wikipedia.org/wiki/Stra%C3%9Fenmarkierung [2] https://en.wikipedia.org/wiki/Speedometer#International_agreements https://en.wikipedia.org/wiki/Speedometer#International_agre...

CraigJPerry 7y ago

IIRC there’s a script written in the RC model aircraft community that verifies claimed speed of models by assessing the doppler shift from the video sound track as the plane passes. /me googles https://youtu.be/DZZWtT32ymY https://youtu.be/DZZWtT32ymY

kthejoker2 7y ago
But to the point of faking it seems like it'd be even easier to generate a fake audio "shift" of your claimed speed.

Jamwinner 7y ago

Most motorbikes overstate speed for whatever reason. Usually by 2-5%. I would agine your estimate was more accurate. There is a whole industry for correcting motorcycle speedometers.

kart23 7y ago

Its speedo error. Most cars and motorbikes slightly overestimate speed, and the effect is more pronounced at higher speeds. This is just to be on the safe side with regards to speed, as tire tread, tire size, temperature, etc. can all have positive or negative effects on speed. Its usually around 5%. You can test this by driving at a constant speed near those radar speed detectors and observing the speed on the board vs. your speedometer. My speedometer is usually about 4 mph faster at 50 mph.

akiselev 7y ago
Note that those road side systems are usually only used as a road sign and the vast majority (at least in California) use a cheaper and less accurate/repeatable sensor than the ones used by police for speed infractions. This is especially pronounced on highways where the same sensor can give you several different readings at 1-10 mph less than actual speed.
- kart23 7y ago
  Or use the gps speed from google maps. That should be pretty accurate.

EthanHeilman 7y ago

What if the video was just sped up? I guess you could use the speeds of the other vehicles as a reference point assuming they are going around the speed limit. It would be harder to show that the video wasn't sped up if there were no other vehicles on the road.