[peter47]

Has anyone else noticed that it appears they have an inbuilt over-read in the speed indication. Here in Aus they seem to have been programmed to over-read by 4kph, no matter what the speed, so it's not simply a percentage error. This has been confirmed by a 'Wheels' magazine road test as well. That is at 100kph you are actually, by GPS, doing only 96. Same 4kph difference right through the speed range..? I suspect it is to make sure there can be no chance of inadvertent speed excess of limit by speedo error, but it does seem a bit of an over-kill. Mazdas appear to have a 2kph over-read as standard, by same 'Wheels' test. Worth knowing and checking if your car is the same, so you can adjust the cruise appropriately to not annoy folk behind you. One possible plus is that it might allow one, at tyre renewal stage, to slightly increase the sidewall depth for slightly wider footprint and softer ride..? Just a thought...

 

[Speedtek22]

Has anyone else noticed that it appears they have an inbuilt over-read in the speed indication. Here in Aus they seem to have been programmed to over-read by 4kph, no matter what the speed, so it's not simply a percentage error. This has been confirmed by a 'Wheels' magazine road test as well. That is at 100kph you are actually, by GPS, doing only 96. Same 4kph difference right through the speed range..? I suspect it is to make sure there can be no chance of inadvertent speed excess of limit by speedo error, but it does seem a bit of an over-kill. Mazdas appear to have a 2kph over-read as standard, by same 'Wheels' test. Worth knowing and checking if your car is the same, so you can adjust the cruise appropriately to not annoy folk behind you. One possible plus is that it might allow one, at tyre renewal stage, to slightly increase the sidewall depth for slightly wider footprint and softer ride..? Just a thought...

My 245/45R18 upgrade puts the speedo pretty much bang on from what I’ve observed. Almost 2.5 km/h difference at 100km/h over stock size so fairly close to what you’ve indicated

 

[SHCS]

I compared to GPS speedometer yesterday and it fluctuated between 1.5 and 2.5 out between 40 and 80 kph. That being said, I am running the smallest of the recommended tire sizes at 3% smaller than factory.

Will be interesting to see how I'm effected when putting factory wheels back on in spring.

 

[peter47]

This is interesting. From a similar forum here in Aus...
"All cars fell within the parameters of an Australian Design Rule that 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 of more than 10 per cent plus 4km/h"
Obtained from this link here... How accurate is your speedo?
So, here at least, someone could be happily cruising along at about 84kph, thinking they are doing their legal 100kph, (and the speedo accuracy would be within the legal requirement), but blithely ignorant as to why they are often being tail-gated or horn-blasted, causing road rage even. It would appear it is wise indeed to check one's vehicle speedo accuracy, and make the necessary speedo/cruise adjustment if the above is to be avoided.

 

[Speedtek22]

This is interesting. From a similar forum here in Aus...
"All cars fell within the parameters of an Australian Design Rule that 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 of more than 10 per cent plus 4km/h"
Obtained from this link here... How accurate is your speedo?
So, here at least, someone could be happily cruising along at about 84kph, thinking they are doing their legal 100kph, (and the speedo accuracy would be within the legal requirement), but blithely ignorant as to why they are often being tail-gated or horn-blasted, causing road rage even. It would appear it is wise indeed to check one's vehicle speedo accuracy, and make the necessary speedo/cruise adjustment if the above is to be avoided.

I always cruise 10 over on the highway anyways…

 

[peter47]

I always cruise 10 over on the highway anyways…

Then you're not the Messiah, but a very naughty boy..!