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Can I use GPS unit instead of the car’s speedometer?

By grdem 7 November 2011 57

Hello, just throwing this out here if anyone knows the answer:

I’m on ACT L’s at the moment and about to take the driving test in a few months. The problem is that my automatic car’s speedometer is busted and too expensive to replace – have to get the part from overseas. The car used to belong to my partner, and he taught me to judge the speed by using the tachometer and listening to the engine.

I’d rather not hire/borrow an unfamiliar car for the driving test, so my question is: can I take the driving test in my car, if I install one of those little GPS units that show the speed as well? Or in fact, can I take the driving test with my smartphone mounted on the dashboard with a speedometer app?

Thanks in advance if anyone can help with this!

What’s Your opinion?


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57 Responses to
Can I use GPS unit instead of the car’s speedometer?
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jayskette 7:30 pm 08 Nov 11

Go ahead and do your test in your car in that state. I promise you sooner or later someone will pass… seeing all sorts of driver behaviour in this fine city, not having a speedo would be the least of your worries!

mopsymannie 2:05 pm 08 Nov 11

You should take your broken car with the GPS. Let us know how it goes. I need a good laugh.

Catty 10:43 am 08 Nov 11

I’d rather try that then give someone the option of cancelling a test because you’ve admitted that your car isn’t fully functional.

Your comment does not make sense – you’d try it, but then give them the option? Oh, you mean “than”
not “then”. Well, that does make sense. “Than” is for comparison, “then” refers to time. It’s not that hard. Grammar does matter!

watto23 9:58 am 08 Nov 11

Henry82 said :

Solidarity said :

Are you sure? I would have thought that being the judge of road-worthiness is not something the intructor would be too keen about, considering it’s not thier job. They’re an instructor, not a roadworthy inspector.

They need to be safe in the car, i wouldn’t want to get into a car i know is unroadworthy. Particularly with someone who hasn’t actually passed their driving test yet. It doesn’t take a mechanic to look at a car, and realise its unroadworthy. Sure theres stuff under the bonet, but anyone can do a basic pre-inspection and be 95% sure the vehicle is in a roadworthy condition.

I can say I failed a driving test due to roadworthyness of the car. The instructor deemed the tyres were not roadworthy and thus the test would not start. This was in my mums suzuki swift 3 cylinder 1.0 litre engine beast of a car. It was red. It was also a while ago now 🙂

p1 9:32 am 08 Nov 11

wildturkeycanoe said :

The inspector will be checking the speed over your shoulder, to make sure you don’t go over the limit. How else are they going to figure it out, ask you what 3000rpm in third means?

What do they do in a car where the speedo is not visible from the passengers seat?

wildturkeycanoe 6:05 am 08 Nov 11

Definitely NOT going to get your license in that car. The inspector will be checking the speed over your shoulder, to make sure you don’t go over the limit. How else are they going to figure it out, ask you what 3000rpm in third means?
Thought for the day – “When a car turns on an empty road, does anyone see it indicate?”

Henry82 11:45 pm 07 Nov 11

p1 said :

I enjoyed driving more. I think banning speedos from all cars would actually make roads safer.

I understand your argument of “focusing on the road”, however plenty of drivers would find other distractions. Anyway, It isn’t that difficult to estimate the speed as you’re driving along. I can get my estimations to within 5km/hr of the speedo. Once you sit on the speed limit, just by listening to the engine noise you can keep at a constant speed (in flat canberra anyway)

I-filed 11:17 pm 07 Nov 11

This can’t be serious – OP is having a lend of you all!

p1 10:48 pm 07 Nov 11

Henry82 said :

Grrrr said :

I’m not convinced that a GPS fails that criteria. Would be interested to hear if anyone’s gotten away with it!

I just looked up the ADR (ADR 1803 for your reference). It says speedometers must have an approval marking. Which is an ‘E’ with a circle around it, then a bunch of numbers following. I don’t think i’ve ever seen this on the back of a GPS.

I imagine a GPS with such a mark would be some sort of specialty instrument and doubtless cost a lot more then a replacement cable or speedo from a wrecker…

Henry82 10:26 pm 07 Nov 11

Grrrr said :

I’m not convinced that a GPS fails that criteria. Would be interested to hear if anyone’s gotten away with it!

I just looked up the ADR (ADR 1803 for your reference). It says speedometers must have an approval marking. Which is an ‘E’ with a circle around it, then a bunch of numbers following. I don’t think i’ve ever seen this on the back of a GPS.

p1 10:14 pm 07 Nov 11

When I broke my speedo cable earlier in the year I drove around without one for ages. While I used a gps a few times out of curiosity and nerdish curiosity, I think I mostly just went with the traffic flow and erred on the slow side to be safe. It took a few days to get used to not having the speedo to look at, but when I did (get used to it) I enjoyed driving more. I think banning speedos from all cars would actually make roads safer.

As for that ridiculous anchor example….. Obvoiusly you would need two. On each side for turning corners and both together in order to stop.

LSWCHP 10:04 pm 07 Nov 11

justsomeaussie said :

Contrary to the people guessing on here. You’ll find that GPS will give you a more accurate reading of your speed than your speedometer. Speedometer’s are traditionally calibrated to be 8km under what your actual speed is. It’s to give you the perspection of driving faster than you are. GPS on the other hand can give a much closer approximation of your real speed over enough distance. Also noting that GPS has an error of 6-10m.

I believe everything I read on the internet. Except for this.

POK 9:23 pm 07 Nov 11

You can’t seriously think that assisted gps can beat a mechanical system in terms of accuracy? There are a lot of things that can mess with the signal, as anyone who has ever used a damned smartphone would know. The time to receive, then to calculate the position and render it alone would create a lag. Because the iPhone/smartphones are not designed to be used in lieu of a speedo, their quality of service will differ greatly. For example, in the event of a major disaster, weather event or holiday the tower speed could degrade. The smartphones do not typically make a display of current latency, cell handovers and so forth so the driver would have no idea that they’re being fed bad data.

The OP said something about just following other drivers. My previous car had a very accurate speedo. Canberra drivers do NOT typically drive anywhere near the limit. When I took my test, my instructor made it clear that I was to go at, and sit on, the speed limit. I imagine any competent instructor when told “I cant verify my speed” would just scratch the test right there.
We certainly learn over our lifetimes how our vehicles perform. Do you really think an L plater has driven her auto so much that she not only knows which gear its in, but can accurately figure out her speed via tacho on varying slopes?
If OP is for real, she needs to hire a car or a get a loaner from a friend.

justsomeaussie 8:44 pm 07 Nov 11

Contrary to the people guessing on here. You’ll find that GPS will give you a more accurate reading of your speed than your speedometer. Speedometer’s are traditionally calibrated to be 8km under what your actual speed is. It’s to give you the perspection of driving faster than you are. GPS on the other hand can give a much closer approximation of your real speed over enough distance. Also noting that GPS has an error of 6-10m.

That all said. As said above, you still need a speedo to have a roadworthy car.

Grrrr 5:41 pm 07 Nov 11

Henry82 said :

Jesus, i can’t believe it. Yes its an instant fail. The car must be roadworthy.

As posted by sarahsarah, the following applies:

1.43 Speedometers
(1) A motor vehicle (other than a trailer) built after June 1974 that can be driven faster than 50km/h on a level road must be fitted with a
speedometer.
(2) The speedometer must—
(a) indicate the speed at which the vehicle is being driven in
kilometres per hour; and
(b) indicate, when the vehicle is travelling faster than 40km/h, a speed that is not over 10% less than the actual speed; and
(c) be readily visible to the driver.

I’m not convinced that a GPS fails that criteria. Would be interested to hear if anyone’s gotten away with it!

Henry82 said :

GPS’ are not accurate, if you go through a tunnel, the signal is blocked, you go on curvy roads etc etc you will not get an accurate indication of speed. Oh and its not instantaneous either.

Sounds like you’ve never driven with a GPS.

An analog speedo isn’t instantaneous either! GPSes
– typically update once per second and may be averaged over several seconds, which is sufficient for driving purposes.
– are far more accurate than the average analog speedo
– are unaffected by changes in tyre wear, air pressure, etc.
– accuracy is not affected by curvy roads.
– could make use of accelerometers to update speed when signal is lost (but I couldn’t name a model that does..)

Henry82 said :

grdem said :

Also, if you know which gear the car is in and can read the revs on the tachometer, you can get a pretty good gauge of speed.

Revvs isn’t displayed in km/hr, and it isn’t “accurate”

Just as accurate as an analog speedo. Anyone with a tacho in their manual car will sooner or later have figured out the ratio of each gear, and thus know their speed from the revs. (3000rpm in 4th = 82kmh, etc)

Henry82 5:31 pm 07 Nov 11

Solidarity said :

Are you sure? I would have thought that being the judge of road-worthiness is not something the intructor would be too keen about, considering it’s not thier job. They’re an instructor, not a roadworthy inspector.

They need to be safe in the car, i wouldn’t want to get into a car i know is unroadworthy. Particularly with someone who hasn’t actually passed their driving test yet. It doesn’t take a mechanic to look at a car, and realise its unroadworthy. Sure theres stuff under the bonet, but anyone can do a basic pre-inspection and be 95% sure the vehicle is in a roadworthy condition.

harvyk1 5:23 pm 07 Nov 11

Solidarity said :

Are you sure? I would have thought that being the judge of roadworthiness is not something the intructor would be too keen about, considering it’s not thier job. They’re an instructor, not a roadworthy inspector.

Whilst I’m pretty sure that OH&S guidelines would require a driving instructor to do a quick check over of the car and anything obviously wrong would prevent the instructor from hoping into the car, maybe a driving instructor \ examiner could jump on and advise if checking that a car is in their opinion safe to drive a deal breaker when it comes to getting a license?

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