Is it standard practice for car manufacturers to deliberately have the speedo reading (of your stock standard vehicle) at 10% less than the actual speed of the car? My last 3 vehicles plus others I have driven have all had the same lower than actual speed. Having checked against numerous GPS readings I have found it to be a fairly consistent situation (unless of course the GPS is out each time??? 
I haven't been fined for driving at the "correct" GPS speed and it seems this is the same as the general flow of traffic.
No, that is not normal. I think the Aus standard was meant to be that the speedo was allowed to read higher than the actual speed, by up to 10%, but never lower than the actual speed at all.
I don't think I have ever had a car that read lower than actual. My current one shows the speed to be just about the same as GPS speed, which I thought was unusual as I have become used to them showing a higher speed.
I've gps'ed my cars and they all read slower than the actual. Checked with portable gps, phone gps and those installed roadside radars the govt puts in near school zones.
Audi 2k slower than 60k
Daihatsu 2k slower
80series 4K slower
Crown 5k slower
These figures obviously increase with speed so 110 in the Crown is only 100.
All on standard tyres and rims.
I've never driven a car that was accurate . It explains why some people sit in the 100 zone right lane doing 90 thinking they're doing the speed limit and won't keep left.
I think you guys maybe mixing up your statements?
"reading slower" means actual speed faster.
believe formula nova is correct, which is also what your experiencing?
Select to expand quoteDunkO said..
I think you guys maybe mixing up your statements?
"reading slower" means actual speed faster.
believe formula nova is correct, which is also what your experiencing?
Y I see what you mean. So my reading is 60/Kph but what I believe is the correct speed by GPS in the Crown is only 55/mph!
I believe (except polies) the federal gov brought this std ruling in many years ago.that all vehicle manufacturers had to have a speedo reading faster than the car is moving. So that no one who got pinged for speeding could take the manufacturer to court for ?? whatever.
I also know a idiot with FG ute who knew his ute inside out and all the speed intricacies that it produced, he them put oversize tyres on and screamed like a virgin when got booked for speeding.
I know all the time what speed my ute is doing, so on the open road SA speed is 110, I set cruise control at 115, this gives me correct speed plus a little extra 
that still falls below radar detection.
As I usually cover 800-1000K a week and mostly open road Ive passed enough patrol cars to know my limits....mind you some other drivers really get ranky about speeding idiots 
In my car it's a feature, there is a setting in the car configuration file, +kph, +2%.
Unfortunately the setting is locked..
Select to expand quotekk said..
In my car it's a feature, there is a setting in the car configuration file, +kph, +2%.
Unfortunately the setting is locked..
That's interesting , so what car is it?
I drive past a camera every day with the cruise control on 86 in an 80 zone and I don't get pinged
Select to expand quoteAUS1111 said..
I drive past a camera every day with the cruise control on 86 in an 80 zone and I don't get pinged
yeah correct...................86
minus -------- 3
actual speed = 83 radar will only pick up 5K over LEGAL SPEED limit not what your speedo reads
Just as an aside, I use the Metroview GPS app on my phone most of the time because it shows the GPS speed and the speedzone, and it uses downloadable maps so it doesn't need data when its running.
I suspect that more and more people are using GPS speeds in their cars or speedos are getting set more accurately as I have noticed in the last few years that people seem to be more closer to the speed limit than I noticed before, except in WA where they are 10 to 20kms less in the right lane and exactly the same in the left lane when being overtaken.
My commodore surf wagon reads high by about 2% the mazda 2 reads high by about 8%. From memory the allowable margins are, never under, between 0 and 8% over, but I could be wrong, it may be 10%
Select to expand quoteslammin said..kk said..
In my car it's a feature, there is a setting in the car configuration file, +kph, +2%.
Unfortunately the setting is locked..
That's interesting , so what car is it?
It's a Land Rover Discovery, the CCF (Car Configuration File) is a carry over from the days of Ford owning Land Rover/ Jag. Most of the settings can be changed with an appropriate tool, but not that one. Most people who care, not me, change the tyre size in the CCF.
Yes, I think most modern cars will be around that 8% high. You can tell by the speed of the slow lane, if I sit the mazda on a 100 that's what every body else is doing. If I sit the commodore on a 100 I'm passing them.
Select to expand quoteTonz said..AUS1111 said..
I drive past a camera every day with the cruise control on 86 in an 80 zone and I don't get pinged
yeah correct...................86
minus -------- 3
actual speed = 83 radar will only pick up 5K over LEGAL SPEED limit not what your speedo reads
Yep that was roughly my calculation - the problem is that cruise controls like being set on numbers ending in zero, so it can be tricky getting it onto 86.
OK, so I got the wrong end of this thread. Thought it was confessing to the times you've jumped in your car in speedo's for a quick dip at the beach only to have to dash into the servo for fuel......
There you go www.legislation.gov.au/Details/F2006L01392/Html/Text Section 5.3 has the formula used.
or this autoexpert.com.au/posts/how-accurate-is-my-cars-speedo
Select to expand quoteAUS1111 said..Tonz said..AUS1111 said..
I drive past a camera every day with the cruise control on 86 in an 80 zone and I don't get pinged
yeah correct...................86
minus -------- 3
actual speed = 83 radar will only pick up 5K over LEGAL SPEED limit not what your speedo reads
Yep that was roughly my calculation - the problem is that cruise controls like being set on numbers ending in zero, so it can be tricky getting it onto 86.
Really? I know on commodores I have owned in the past, each increment seemed to be 1.6kms, obviously based on something from the USA, but other cars I have noticed that they had increments of 2kms.
A cruise control that is set only on multiples of ten? Can't you just get to the target speed and then set it?
My Camry displays a speed lower than actual by about 3%. (ie. when my speedo says 100, my GPS says 103).
Since most new cars display about 5% more than actual, it explains why I am always passing people on the freeway.
The current Australian Design Rules (ADR) prohibits any under-reading:
"5.3. The speed indicated shall not be less than the true speed of the vehicle. At the test speeds specified in paragraph 5.2.5. above, there shall be the following relationship between the speed displayed (V1 ) and the true speed (V2).0 less than or equal to (V1 - V2) less than or equal to 0.1 V2 + 4 km/h."
I'm waiting for the day when they book you based on what the speedo in your car reads and say that is the speed they go on, as real speed is no longer valid.
The cops would know that if you're in a modern car sitting on 110 in a 110 zone, that your car tells you it's too fast, so then they have to decide if they want to try and bluff you, your word against theirs. Good luck!
Just have a GPS logger running, then you have proof of your speed. Just make sure you stay below the speed limit.
Select to expand quoteFormulaNova said..AUS1111 said..Tonz said..AUS1111 said..
I drive past a camera every day with the cruise control on 86 in an 80 zone and I don't get pinged
yeah correct...................86
minus -------- 3
actual speed = 83 radar will only pick up 5K over LEGAL SPEED limit not what your speedo reads
Yep that was roughly my calculation - the problem is that cruise controls like being set on numbers ending in zero, so it can be tricky getting it onto 86.
Really? I know on commodores I have owned in the past, each increment seemed to be 1.6kms, obviously based on something from the USA, but other cars I have noticed that they had increments of 2kms.
A cruise control that is set only on multiples of ten? Can't you just get to the target speed and then set it?
I should clarify (this is on a VW) you can set it on whatever speed you like, but if you change speed zones and want to nudge it up or down to the next level, it only goes in 10kmh increments, so you have to kind of fiddle around to find 66/76/86 etc. In WA the speed limit changes every couple of hundred metres so this is quite distracting.
Is there anywhere else in the world that has 40/50/60/70/80/90/100/110kmh limits??? Combine that with a speedo that reads 4kmh over, and exits / entries on both the left and the right side of the freeway, and it all gets a bit distracting, especially if you've had a few 
My Subaru uses a quick nudge for 5kph increments, slow nudges for 1kph increments, or press and hold to scroll up or down in 1kph increments.
Select to expand quoteHarrow said..
My Camry displays a speed lower than actual by about 3%. (ie. when my speedo says 100, my GPS says 103).
Since most new cars display about 5% more than actual, it explains why I am always passing people on the freeway.
Are you running the correct tyre/wheel combination or the same effective size? This would be the most likely reason.
Select to expand quoteAUS1111 said..FormulaNova said..AUS1111 said..Tonz said..AUS1111 said..
I drive past a camera every day with the cruise control on 86 in an 80 zone and I don't get pinged
yeah correct...................86
minus -------- 3
actual speed = 83 radar will only pick up 5K over LEGAL SPEED limit not what your speedo reads
Yep that was roughly my calculation - the problem is that cruise controls like being set on numbers ending in zero, so it can be tricky getting it onto 86.
Really? I know on commodores I have owned in the past, each increment seemed to be 1.6kms, obviously based on something from the USA, but other cars I have noticed that they had increments of 2kms.
A cruise control that is set only on multiples of ten? Can't you just get to the target speed and then set it?
I should clarify (this is on a VW) you can set it on whatever speed you like, but if you change speed zones and want to nudge it up or down to the next level, it only goes in 10kmh increments, so you have to kind of fiddle around to find 66/76/86 etc. In WA the speed limit changes every couple of hundred metres so this is quite distracting.
Is there anywhere else in the world that has 40/50/60/70/80/90/100/110kmh limits??? Combine that with a speedo that reads 4kmh over, and exits / entries on both the left and the right side of the freeway, and it all gets a bit distracting, especially if you've had a few
Ahh, okay, that makes sense. I have never had a car with that clever sort of cruise control so I didn't know you could do that. As a comparison my current car just has a single button for set and reset and doesn't even have a resume feature. Mind you, the factory cruise control has radar tracking, and I have just got an aftermarket one.
Sydney has the same thing with the speed limits all over the place, but thankfully the right hand exits are not that common. They are not a good idea unless you are trying to get the mindless drivers to exit the freeway.
On top of the ADRs for the speedo having the 10% tolerance, erring on the side of caution, your odometer will probably be close to spot on so you don't get an extra 10% worth of kilometres on your warranty mileage for free.
Yep so this deliberate inaccuracy, combined with speed cameras, is what results in 3 cars side by side on the freeway doing 92 in the 100 zone, clogging up the road. Morons.
