I was driving my BIL’s VW Golf, which has a GPS Speedo as well as the regular one. There’s a ~4 Kph difference between the two, with the GPS one being the lowest. My BIL, very knowledgeable in car stuff, says the GPS one is the most accurate. Is he right or should I be using the car one as reference? (It could be the difference between a speeding fine and not 😜)
Divine Angel said:
I was driving my BIL’s VW Golf, which has a GPS Speedo as well as the regular one. There’s a ~4 Kph difference between the two, with the GPS one being the lowest. My BIL, very knowledgeable in car stuff, says the GPS one is the most accurate. Is he right or should I be using the car one as reference? (It could be the difference between a speeding fine and not 😜)
GPS is the more accurate, the speedo becomes less accurate, on the high side, the faster you go.
The speedo measures the rotational speed of the wheels, and uses the presumed wheel size to calculate the car’s speed. GPS measures the rate the car’s position on the earth is changing, so is more accurate.
You can check it against a tachymetre if you’ve got accurate markers along a freeway.
Timed against a 1km course:
33s = 110km/hr
36s = 100km/hr
40s = 90km/hr
Speedos allow for great accuracy.
Divine Angel said:
I was driving my BIL’s VW Golf, which has a GPS Speedo as well as the regular one. There’s a ~4 Kph difference between the two, with the GPS one being the lowest. My BIL, very knowledgeable in car stuff, says the GPS one is the most accurate. Is he right or should I be using the car one as reference? (It could be the difference between a speeding fine and not 😜)
This is correct. Car speedos are abysmal. Rely on the GPS one.
My main car reads out by 9 km/hr at 110 km/hr. So long as it’s out by less than 10% on the high side it’s legal. Car manufacturers deliberately set their speedometers wrong in order to fake their acceleration and top speed figures. I strongly suspect that the fakery continues into odometer figures, resulting in extra income from unnecessarily early maintenance and resulting in falsely low car resale value.
Speedo inaccuracy is a major cause of frustration on high speed roads. I think we all need to campaign for accurate speedometers, +-1 km/hr max error at recommended tyre pressures.
Since the last time this thread appeared on the forum I’ve been timing the time lag of GPS speed during rapid accelleration and braking. The time lag averages out to about 3 seconds, which is too fast to create any significant error during cornering.
mollwollfumble said:
Speedo inaccuracy is a major cause of frustration on high speed roads. I think we all need to campaign for accurate speedometers, +-1 km/hr max error at recommended tyre pressures.Since the last time this thread appeared on the forum I’ve been timing the time lag of GPS speed during rapid accelleration and braking. The time lag averages out to about 3 seconds, which is too fast to create any significant error during cornering.
I think rolling circumference changes too much as tyres wear, and I’m concerned that trilateration accuracy drops on hills, when the vehicle is moving up (toward) or down (away from) the satellites.
(those two being the reasons I prefer the time-over-distance method of the tachymetre.)
Rule 303 said:
mollwollfumble said:
Speedo inaccuracy is a major cause of frustration on high speed roads. I think we all need to campaign for accurate speedometers, +-1 km/hr max error at recommended tyre pressures.Since the last time this thread appeared on the forum I’ve been timing the time lag of GPS speed during rapid accelleration and braking. The time lag averages out to about 3 seconds, which is too fast to create any significant error during cornering.
I think rolling circumference changes too much as tyres wear, and I’m concerned that trilateration accuracy drops on hills, when the vehicle is moving up (toward) or down (away from) the satellites.
Not by more than 2%. In either case.
Australian Speedo accuracy standards
Australian Design Rule 18 sets out the accuracy standards for vehicle speedos.
Until July 2006 this rule specified an accuracy of +/- 10 percent of the vehicle’s true speed when the vehicle was travelling above 40km/h.
That is, at a true vehicle speed of 100km/h the speedo could indicate between 90km/h and 110km/h.
An odometer accuracy of +/- 4 percent was also a requirement.
From July 1 2006 a new standard began its phase in and by 1 July 2007 all new vehicles had to comply. The new standard requires that:
The speedo must not indicate a speed less than the vehicle’s true speed or a speed greater than the vehicle’s true speed by an amount more than 10 percent plus 4 km/h.
Odometer accuracy is no longer defined.
What this means:
For a vehicle travelling at a true speed of 100km/h, the speedo must read between 100km/h and 114km/h. The effect of this is that many drivers will find that at 100km/h they are driving up to 14km/h below the speed limit if they rely on the vehicle’s speedo.
The speedo must always read ‘safe’, meaning the vehicle must not travel faster than the speed indicated by the speedo.
This change was made to align Australian vehicle rules with those already in place in Europe. It applies to all Australian motor vehicles except mopeds.
Dealers will generally not attempt to correct speedo error unless it exceeds the legal requirements.
mollwollfumble said:
Rule 303 said:
mollwollfumble said:
Speedo inaccuracy is a major cause of frustration on high speed roads. I think we all need to campaign for accurate speedometers, +-1 km/hr max error at recommended tyre pressures.Since the last time this thread appeared on the forum I’ve been timing the time lag of GPS speed during rapid accelleration and braking. The time lag averages out to about 3 seconds, which is too fast to create any significant error during cornering.
I think rolling circumference changes too much as tyres wear, and I’m concerned that trilateration accuracy drops on hills, when the vehicle is moving up (toward) or down (away from) the satellites.
Not by more than 2%. In either case.
Where is this figure from?
assuming you’re using a foot on the accelerator, I would think creep and speed trending up before corrections are made to be the bigger problem/risk.
nothing wrong with using the whatever that gives the highest indication of speed, which’ll give a better margin for corrections^
last time I checked too the speed limit wasn’t some objective velocity a driver is meant to get a near possible, though informal aspects of behavioral influences incline it.
> The speedo must always read ‘safe’, meaning the vehicle must not travel faster than the speed indicated by the speedo.
That’s bullshit. That’s not “safe”. That’s like insisting that all wristwatches run fast.
mollwollfumble said:
> The speedo must always read ‘safe’, meaning the vehicle must not travel faster than the speed indicated by the speedo.That’s bullshit. That’s not “safe”. That’s like insisting that all wristwatches run fast.
mollwollfumble said:
> The speedo must always read ‘safe’, meaning the vehicle must not travel faster than the speed indicated by the speedo.That’s bullshit. That’s not “safe”. That’s like insisting that all wristwatches run fast.
probably means “safe” in that you don’t get booked for speeding. maybe why they put quotes around the word.
ChrispenEvan said:
mollwollfumble said:
> The speedo must always read ‘safe’, meaning the vehicle must not travel faster than the speed indicated by the speedo.That’s bullshit. That’s not “safe”. That’s like insisting that all wristwatches run fast.
probably means “safe” in that you don’t get booked for speeding. maybe why they put quotes around the word.
Also you are going slower than you think you are.
ChrispenEvan said:
mollwollfumble said:
> The speedo must always read ‘safe’, meaning the vehicle must not travel faster than the speed indicated by the speedo.That’s bullshit. That’s not “safe”. That’s like insisting that all wristwatches run fast.
probably means “safe” in that you don’t get booked for speeding. maybe why they put quotes around the word.
“Safe” is all vehicles travelling the same speed. Because then there are no collisions.
The wrong speedo scam is to make fines for speeding easier to collect on.
mollwollfumble said:
ChrispenEvan said:
mollwollfumble said:
> The speedo must always read ‘safe’, meaning the vehicle must not travel faster than the speed indicated by the speedo.That’s bullshit. That’s not “safe”. That’s like insisting that all wristwatches run fast.
probably means “safe” in that you don’t get booked for speeding. maybe why they put quotes around the word.
“Safe” is all vehicles travelling the same speed. Because then there are no collisions.
The wrong speedo scam is to make fines for speeding easier to collect on.
LOL, surely as a driver you can judge what speed others are travelling at? It is only when there is a big difference in speed that it becomes dangerous and those speeds would be well outside speedo inaccuracy’s. As to the fines, LOL, speedos over estimate your speed so you will be under posted limits not over.
ChrispenEvan said:
mollwollfumble said:
ChrispenEvan said:probably means “safe” in that you don’t get booked for speeding. maybe why they put quotes around the word.
“Safe” is all vehicles travelling the same speed. Because then there are no collisions.
The wrong speedo scam is to make fines for speeding easier to collect on.
LOL, surely as a driver you can judge what speed others are travelling at? It is only when there is a big difference in speed that it becomes dangerous and those speeds would be well outside speedo inaccuracy’s. As to the fines, LOL, speedos over estimate your speed so you will be under posted limits not over.
Quite right.
also, the more worn your tyres are, the slower your actual speed will be wrt the speedo.
(full tread 16, 60, 195s have a circumference 2.5cm longer than the same tyre worn to the tread markers)
ChrispenEvan said:
]LOL, surely as a driver you can judge what speed others are travelling at?
though seeing how people attempt merging i am not so sure some drivers do.
Stumpy_seahorse said:
also, the more worn your tyres are, the slower your actual speed will be wrt the speedo.(full tread 16, 60, 195s have a circumference 2.5cm longer than the same tyre worn to the tread markers)
Ooh, I got four new tyres last week. So I will be going faster again now! My fuel consumption is always best just before I get new shoes.
Stumpy_seahorse said:
also, the more worn your tyres are, the slower your actual speed will be wrt the speedo.(full tread 16, 60, 195s have a circumference 2.5cm longer than the same tyre worn to the tread markers)
AFAIK speedos are calibrated on half worn standard equipment tyres at manufacturers recommended pressures.
buffy said:
Stumpy_seahorse said:
also, the more worn your tyres are, the slower your actual speed will be wrt the speedo.(full tread 16, 60, 195s have a circumference 2.5cm longer than the same tyre worn to the tread markers)
Ooh, I got four new tyres last week. So I will be going faster again now! My fuel consumption is always best just before I get new shoes.
:)
Tamb said:
Stumpy_seahorse said:
also, the more worn your tyres are, the slower your actual speed will be wrt the speedo.(full tread 16, 60, 195s have a circumference 2.5cm longer than the same tyre worn to the tread markers)
AFAIK speedos are calibrated on half worn standard equipment tyres at manufacturers recommended pressures.
Falcons since the E series and commodores from 2nd gen on have been calibrated at 5km below at 100kph as they rolled out of the factory with brand new equipment
mollwollfumble said:
ChrispenEvan said:
mollwollfumble said:
> The speedo must always read ‘safe’, meaning the vehicle must not travel faster than the speed indicated by the speedo.That’s bullshit. That’s not “safe”. That’s like insisting that all wristwatches run fast.
probably means “safe” in that you don’t get booked for speeding. maybe why they put quotes around the word.
>“Safe” is all vehicles travelling the same speed. Because then there are no collisions.
:) yeah, well, that’s partly true, contributes to the conformity of traffic flow, but it also contributes to traffic compression which results in reduced braking distances, meaning breaching safe braking distances is quite the norm, necessity even in practice.
people get their speed perspective (for calibration) very much from vehicles ahead and behind. People think this way also, as you’re perhaps doing, without knowing it, in fact it more generally influences behavior.
so effective are the unconscious aspects of driving on behavior, that the average person hasn’t ever considered in detail the difference between a safe braking distance (or safe trailing distance), as contrasted with establishing it, which aren’t the same thing. The only exception to them being two different things is when approaching another vehicle (from behind for example) and its velocity is unknown, in the case it is in fact not moving or traveling very slow. Paradoxically it requires considering them as distinct things to understand when they are not.
to the question, speed measuring devices always have some error.
the likely error is made to be more likely in the – (minus) parameter of the +/- accuracy (of real ground speed), allowing for tyre wear, parallax, whatever, it’s never perfect, and arguments with the police are going to be fewer. So over-read is like a prophylactic.
but if you push right up the the speed limit, then there are going to be conversations like this.
The wrong speedo scam is to make fines for speeding easier to collect on.
>The wrong speedo scam is to make fines for speeding easier to collect on.
and that above ^ wasn’t meant to be part of my text
which don’t agree with, while i’m at it
NSW uses “CHECK YOUR SPEED” radars. My 16 y.o. Toyota Camry’s speedo reads very close to the radar.
Knowing your exact speed is not a significant factor in road safety imo (as the official holiday road toll in NSW reaches 21 so far)
Are there reliable apps that alert you when you’re over the local speed limit?
dv said:
Are there reliable apps that alert you when you’re over the local speed limit?
Wallopers.com.au
dv said:
Are there reliable apps that alert you when you’re over the local speed limit?
Your GPS machine will BING when you go over the speed limit.
Are you still os sibeen?
dv said:
Are there reliable apps that alert you when you’re over the local speed limit?
Most Sat Navs can tell you, although they don’t account for lowered speed limits such as roadworks.
its the margin or error of the police speed detector thats applicable not the car speedo or GPS. if their unit is out you can claim all you want you were going the speed limit.
speed limits are about catering to the lowest IQ to safely drive
notice australia has been lowering its speed limits whilst germany has open speed limits on the autobahn.
wookiemeister said:
speed limits are about catering to the lowest IQ to safely drive
…./cut….
it’s easy to think that
image though, two lanes, you’re in the left lane, and oncoming traffic in in the right lane, you decide to pass a vehicle, how, I ask, if there is no certainty about the speed of oncoming traffic do you compute the convergence rate.
the convergence (rate) is your time to safely overtake.
there’s more….
imagine you’re the oncoming vehicle, someone pulls out ahead to pass, if you’re both within the speed limit (not over it), then both are in a better position to compute convergence rates, and you might slow rapidly, pull off the road the let the oncoming vehicle overtake, an emergency.
speeding and unknown speeds that way compromise things.
transition said:
wookiemeister said:
speed limits are about catering to the lowest IQ to safely drive
…./cut….
it’s easy to think that
image though, two lanes, you’re in the left lane, and oncoming traffic in in the right lane, you decide to pass a vehicle, how, I ask, if there is no certainty about the speed of oncoming traffic do you compute the convergence rate.
the convergence (rate) is your time to safely overtake.
there’s more….
imagine you’re the oncoming vehicle, someone pulls out ahead to pass, if you’re both within the speed limit (not over it), then both are in a better position to compute convergence rates, and you might slow rapidly, pull off the road the let the oncoming vehicle overtake, an emergency.
speeding and unknown speeds that way compromise things.
Agree.