What device/s can u use in/on your car to record your vehicle speed accurately?

[r4ndll Avid PP Poster! Find all posts View Profile Close r4ndll]

Gents.....

Looking for ideas here as to whether there is any devices out there that can accurately record (& store) your vehicle speed during your travels? It has to have some sort of certificate that indicates it's been calibrated and Tested, and be legal to have installed in your vehicle....

Before anyone suggests the most common device - "GPS", that's not a certified &/or tested for accuracy device, etc. There is also the issue of driving up/down hills that can give u a false reading.....

Just some thoughts -

- As already said - digital camera/dashcam with visible timestamp. If pinged, you'd have to go back and find two fixed points on the road (e.g. signpost and tree) where you were pinged, measure them and then use equation Speed=Distance/Time to get your speed

- Fit an additional calibrated speedometer. Or have your existing speedo calibrated by a NATA accredited, ISO 9001/17025 compliant independent testing laboratory

- Purchase a LiDAR system - Google's driverless car's LiDAR system costs about $70,000

- In theory a Doppler radar (its what planes use) but doubt it could be

[rob_macca67 Avid PP Poster! Find all posts View Profile Close rob_macca67]

True..... Also, your Speedo and Odometer can read differently. I know on one of my cars, the speedo is 5% out where as the Odometer is some 9-10% out due to the tyre size I'm running...

It's a good idea of yours but accuracy is the thing as your speed can vary between those 2 points where u are working out the average speed the 2 points and not the MAX speed between the 2 points....

rob

Folks, I don't think we are going to get what rob_macca67 set out to achieve. Despite what symo tells us about GPS accuracy, there is no way Police will accept it. If symo is correct, at 60kmph the GPS COULD be out by 6kmph. More than enough for police to distrust your GPS.
I suggest an alternative. If you have a dash cam that shows the time accurately on its recording, and you can accurately record the time it takes to travel between 2 points, then you can accurately determine the speed you were doing. I recon you would need to have relatively high definition in order to pin point distance traveled in order for a court to accept it.
Aside from that, it's probably good practice to know exactly what you odo and speedo is reading. Does your odo accurately record how far you've gone? At a given speed on your speedo, how long does it take to travel a km? Don't rely on the GPS. It's possibly out by 100m. You can't argue with time and distance.

[B.Col Lurker Find all posts View Profile Close B.Col]

True..... Also, your Speedo and Odometer can read differently. I know on one of my cars, the speedo is 5% out where as the Odometer is some 9-10% out due to the tyre size I'm running...

It's a good idea of yours but accuracy is the thing as your speed can vary between those 2 points where u are working out the average speed the 2 points and not the MAX speed between the 2 points....

rob

And there is the beginning of another thread on fixed v point to point speed detection.

[Just*Managing Member Find all posts View Profile Close Just*Managing]

its all well and good to tell us their machines are all properly calibrated but all we commoners have to work on is the car speedo (i have 4 cars and a motorbike and only 1 of them matches the gps spot on), and of course a GPS. If you have evidence that to the best of your knowledge you were travelling at xx speed, that should be taken in to account. ( I know it won't, just sayin thats all).

[peter_mcc Senior Member Find all posts View Profile Close peter_mcc]

...Despite what symo tells us about GPS accuracy, there is no way Police will accept it. If symo is correct, at 60kmph the GPS COULD be out by 6kmph. More than enough for police to distrust your GPS.

If the GPS has good satellite receiption then the error would be nowhere near that big. Part of the problem using a GPS would be proving that it had enough satellites to give an accurate result.

I suggest an alternative. If you have a dash cam that shows the time accurately on its recording, and you can accurately record the time it takes to travel between 2 points, then you can accurately determine the speed you were doing. I recon you would need to have relatively high definition in order to pin point distance traveled in order for a court to accept it.

I think they'd argue that the timebase on the video wasn't calibrated so you couldn't rely on it to calculate the speed.

Aside from that, it's probably good practice to know exactly what you odo and speedo is reading. Does your odo accurately record how far you've gone? At a given speed on your speedo, how long does it take to travel a km?

Interestingly, my Scangauge shows a different speed to my speedo. The Scangauge matches the GPS speed while the speedo reads under by ~5km/h at 110. It's like the car knows how fast I'm really going but doesn't want to tell me!

Don't rely on the GPS. It's possibly out by 100m.

Not convinced the GPS is likely to be that inaccurate in most situations.

You can't argue with time and distance.

Unless you're the Police... in which case they will argue with anything that might cause them problems enforcing speeding fines :-)

I thought the GPS can only read a horizontal speed and therefore when heading up/down hills, then the speed travelling is not that accurate... ?

Unless you are going up/down a really really steep hill the difference is likely to be very very small. And you're not likely to be going fast enough up/down a hill that steep for it to matter. Looking at the maths, if you're on a 1 in 10 slope the distance travelled down the road is sqrt(1*1 + 0.1*0.1) = sqrt(1.01) = 1.005 - ie you travel 0.5% further on a 1 in 10 slope.


Ultimately the real issue is the lengths the Police will go to so that you can't sucessfully challenge a speeding fine.

The only thing I can see that might help would be one of the monitoring systems used in heavy vehicles - from memory some of them can be used to penalise companies if their trucks are speeding so I'm guessing you could use it the other way too. For most people I imagine the cost/hassle would not be worth the potential return/savings.

[Bushbasher Out of control poster! Find all posts View Profile Close Bushbasher]

my Scangauge shows a different speed to my speedo. The Scangauge matches the GPS speed while the speedo reads under by ~5km/h at 110.

Manufacturer's are not permitted to sell you a car with a speedo that shows a lower speed than your true speed. That's why many speedo's run 4-6km/hr faster than your true speed. That's in the ADRs. Therefor, if you trust your GPS then you are in trouble. I calibrated my scanguage with a mobile radar unit accurate to +_ 2km/hr. With new 70 series BFGs the speedo now matches the scanguage and radar.

[AJ120 Out of control poster! Find all posts View Profile Close AJ120]

I finally remembered to ask about our tracking system at work. They use the Navman fleet tracking and it runs off the mobile phone system apparently, which means it looses tracking once out of mobile range, which may not be useful for a 4wd. As to whether the data collected is of any use in disputing a speeding ticket I couldn't say, but hopefully it gives you an avenue to investigate.

http://navmanwireless.com.au

Cheers Andrew

[Nik83 Member Find all posts View Profile Close Nik83]

GPS has a few limitations. A device with gyro can take into account elevation angles and speed and work out your real speed based on some reasonably simple (and complex, if desired) trigonometry calculations.

That said, when on an angle, your gps signal can be interfered with due to signals lost, gained and incorrect referencing. Think of it like having five spotlights pointing down on you on a reasonably level field, angling in different directions can alter the light painted on the target. The differences when you're charging along at speed can be negligible, but I've seen some interesting results. Take into account also 5-10m accuracy.

There's a lot that comes into it, and good software should accomodate anomalies, but the only true way of getting a good irrefutable readout imho is something with pinpoint and instant accuracy with a static target ... Calibrated Lasers. On board.

You could argue till the cows come home and a court could/might not disregard your device, but the courts do use commercially available devices on board to prosecute... So I guess it's up to the judge on the day. Traffic courts would likely just go for the fine though.