How to read your speedo correctly

[vnv8driver]

This is based on a vn-vp commodore, either v6 or v8 but results would be similar if not the same for most commodores.

Ever wondered why people are 'speeding' past you on the highway when your sitting on what your dash says 100km/h? Its because your not actually doing 100km/h, Thats right at 100km/h your most likely sitting on 95-96km/h!

First off you need a gps or phone with a gps to give you an approximate reading of how fast your going. You then set the cruise control and tap the button until your around 5% over the speed limit.

In my car for example, which has stock standard 15 inch wheels and 65 series tyres, i can be doing a real time speed of 105km/h in a 100km/h zone on the gps but my needle reads 110km/h.


A good little tip that not alot of people know about to get you from point A to point B legally just that little bit quicker, which can be handy at times.

[Ozzie]

theres a speed test on the western freeway that I use to test my speed

sometimes its acurate, other times i wonder.

when i had the stock 15's on @ 110kmph it read 110kmph
when I put the 17"s on it @ 110kmph it reads 113kmph

but ofcourse not everyone is able to drive through a speedtest so nice thread

[vnv8driver]

Since you put the larger wheels on, even though you have the right size duration tyre the speedo will still be out by a few km's

[Rhino Racing]

I am not sure about anywhere else.... but in Qld they have taken on the zero tolerance approach at the beginning of the year and there is no 10% safety margin in there anymore.
That is why you hear of people being done for like 65kph in a 60 zone and 105kph in a 100kph zone.
The people that i have heard that got done like this both have big mouths on them.... and i would say that if they acted civilly to the police they no doubt would have copped a warning only. I would say some of it would come to police discretion.
So dont assume you have 10% in my eyes.

[vnv8driver]

ill look into it, i cant see how they can change a commonly known rule just like that without giving any warning, sounds like id have a field day if that ever happened to me.

[TheyDontWantMusic]

ill look into it, i cant see how they can change a commonly known rule just like that without giving any warning, sounds like id have a field day if that ever happened to me.

it was never a commonly known rule, they've never stated that the law was 10%, people simply assumed that it was, which is very well may have been.

[Benboy]

There is no such thing as a 10% margin for error on speedometers. In some States Speed Cameras are set to record speeds of 2 - 3 km/ph above posted limits. Technically speaking 1 km/ph above a set/prescribed speed limit is an offence. It makes no difference what reading you have recorded on your speedo. If it was incorrect, that's you're bad luck.

[vnv8driver]

^thats right but when the photos go to get processed, the ones only a few km/h dont get sent out, i used to work with a tow truck company and talked to a few coppers, there was/is a 10% margin for error. Im looking into it now to see if it still applies or not.

[Rhino Racing]

^thats right but when the photos go to get processed, the ones only a few km/h dont get sent out, i used to work with a tow truck company and talked to a few coppers, there was/is a 10% margin for error. Im looking into it now to see if it still applies or not.

I think you will find that as a general rule of thumb, that may have been applied in the past. But it is not law! Afaik.
With more accurate, modern devices (radars and cameras) that are calibrated frequently the error in the radar is more than likely negligible.
So they have not changed any law as such. They just do not need to have such a high "margin of acceptable tolerance" as before.
I have found that when checking with a GPS most car manufacturers have their speedos reading 1-5kph lower than actual, i have not found one that reads over the limit with standard tyres and rims fitted.
I believe that in general cops will give you the benefit of the doubt..... unless you act like a tool! In which case people get what they deserve.

[vnv8driver]

that sounds fesible, but its still a good note for people wanting to take advantage of the recalibrated speedo, ill change it now until i know more i might give qld trans a phone tomorrow to find out what the go is.

[Ozzie]

just curious...

This is a dumb question but here I go...

Is there any difference in speed for say a car with bald tyres and a car with brand new tread. Both cars have 15"s standard?

Tread on most standard tyres is like 5mm.. Would it nock the speedo out by much if any at all?

[VrWagz1]

not by much,but yes it will, if your circumfrence becomes smaller then they will travel less distance with each revolution, so you will go slower than your speedo shows. But not by much at all.

[LightningVP]

in Victoria, last I heard it is 3 pts margin, and 10% when over 100. I got caught doing 75km/h in a 60 zone, and was processed as doing 72km/h, but it also depends on the cop some will ask you the same old "did you know you were speeding" and if you are a good lier you can work a warning out of them...not that i am telling people to, lying is wrong

[vnv8driver]

Im with vrwags, i recon it would be out, but not by a great deal.

lightning- im looking into it today (qld) but should be the same aus wide.

[Nevyn]

manufactures have never guaranteed that the speedos were 100% actuate....they are the ones who started the 10% by stating the speedos can be out by up to 10%, that way drivers can't sue them when they get a speeding ticket. With better and more actuate speed cameras & radar guns, at least here in Vic, the tolerance is now down from 10k's to 3k's over.

[Deutscher]

that's kind of gay. I always set my cruise control just slightly over the speed limit (mainly so I don't get abused for going too slow), but if you can get done for 3kms over, THATS GAY!

[kopper69]

I remember reading in the Wheels magazine (I think it was wheels) in late 2006 when the VE had just been released about the speed they were travelling when their instrument cluster said 100km/hr. I assumed the speed was measured on a radar and it said that all of the brand new VE's would only be doing 96km/hr when their speedo read 100km/hr. I have had my GPS in my car and found that my speedo is about 10% under. So when my speedo says 110 Im really only doing 100. The only change I have is 16" rims instead of the 15". When I first started driving I wondered why everyone was always sitting just over the speed limit, then found out that most people did sit right on the speed limit, it was just my speedo was out.

I have checked with the GPS in other cars, VT, VX, ford territory, ford G6E, toyota echo and found that they were almost exactly spot on in every one - as in the GPS matched exactly the speedo reading. Just my VR that has the inaccuracy. For those interested you can have your speedo calibrated too if you would like it fixed up. Dont just assume that your speedo is out though and sit above the speed limit - the excuse wont work on Mr Policeman.

[XeKToReX]

victoria is 3km/h when under 100km/h, 3% when over.. its on my fine here..

[Nevyn]

thats odd...my last speeding ticket was for exceeding 100km/h but under10km/h....nothing about 3%

[XeKToReX]

hmm.. yeah under 10 is the charge, my orig one said it but 2nd notice says alleged is 2km/h under detected

[Philthy]

They always give a k or 2 leeway on camera fines to account for errors, but it is now 'no tolerance' to the limit. (from the few fines I've seen)
Realistically though, no cop is going to ping you, then chase you down and pull you over for doing 2 or 3 over the limit

[ratz26]

not sure if its been mentioned yet...not gunna sit here and read everyone posts..
dont follow ur GPS for speed..ALL gps's are 5 - 10% out so when ur GPS says ur doing 110 ur actually doing 100..this happens due to the "LAG" from the time it takes the signal to get from the satilite to your GPS.

[FXST01]

not sure if its been mentioned yet...not gunna sit here and read everyone posts..
dont follow ur GPS for speed..ALL gps's are 5 - 10% out so when ur GPS says ur doing 110 ur actually doing 100..this happens due to the "LAG" from the time it takes the signal to get from the satilite to your GPS.

The lag would depend on how long you were travelling at that speed for, travel at any speed for a decent period of time and the lag will be irrelevant.

[immortality]

most pathetic thread really. speedo's are calibrated fast to save most people from themselves and prevent that accidental speeding ticket. another goverment conspiracy maybe

[vlv8vic]

not sure if its been mentioned yet...not gunna sit here and read everyone posts..
dont follow ur GPS for speed..ALL gps's are 5 - 10% out so when ur GPS says ur doing 110 ur actually doing 100..this happens due to the "LAG" from the time it takes the signal to get from the satilite to your GPS.

no way! do you actually know how these things work? Apart from digging a pretty OLD and dead thread you are providing misinformation.
I suggest you find out how these things work before you dump another gem of wisdom.

Yes, there will be lag but it doesn't cause your gps to be 'out' in any way. It will read the speed you were doing a second, maybe 10 even (signal, model etc etc). but at a constant speed it is as accurate as you'll ever get.