sat nav speed -v- speedometer

patrickc

theres always posts here about the inaccuracies of speedometers, so which would be more accurate, sat nav or my speedometer

when i'm doing 70mph according to the cars clock, the sat nav says i'm doing 66mph, and so on.

Mental Mickey

patrickc wrote: »

theres always posts here about the inaccuracies of speedometers, so which would be more accurate, sat nav or my speedometer

when i'm doing 70mph according to the cars clock, the sat nav says i'm doing 66mph, and so on.

Erm.............I would guess the speedometer in the car would be more accurate??

patrickc

Mental Mickey wrote: »

Erm.............I would guess the speedometer in the car would be more accurate??

i dont know, i know people here always say your car's speedo can be out by as much as 10%

Niall1234

Yep.

Cars speedometers constantly over read. Different manufacturers cars over read by more or less.

I hear FIAT are the worst at 10%. The reason is that they rather to err on the side of caution incase anyone thinks of suing them over getting speeding fines etc.

-Chris-

Speedometers aren't accurate. They're nearly all overestimating the speed. The varience is greatest at low or high speeds.

AFAIK speedos must be calibrated so that they don't underestimate the speed and never overestimate the speed by more than 10%.
Edit: Beaten to it (twice!!)

As for Sat Nav, it would probably depend on a lot of conditions - from where you are to the quality of the Nav system you're using to what the weather conditions and cloud cover are like... Anyone else know more?

Oilrig

SatNav will measure your speed between two points on a flat map. In other words it doesn't know whether you're traveling up or down a hill thus covering more distance.

Bottom line, unless you're driving along a perfectly flat road, your sat nav speed will be inaccurate.

patrickc

Oilrig wrote: »

SatNav will measure your speed between two points on a flat map. In other words it doesn't know whether you're traveling up or down a hill thus covering more distance.

Bottom line, unless you're driving along a perfectly flat road, your sat nav speed will be inaccurate.

well when i checked both speeds, i was on the motorway, so was pretty flat..

Eoin

My speedo and GPS are usually within 2MPH or so of each other.

E92

Satnav speed is the actual speed if you're on the flat. Satnav doesn't know what hills are though.

Speed cameras actually allow a 10% discrepancy, as speedos have to be accurate + or - 10%. So if the limit is 100 km/h, you can actually do 110.

In any event, if you're actually travelling at 100 km/h, your speedo will probably display between 105 and 110. They're always set to overread the speed you're travelling at.

Senna

my toyota reads 114kmph when the sat nav say 100kmph. I've checked the speed quite a few times (always) on the flat and it's constantly out by 14% at 100KMPH.
When i bought the car first there was a speed converter in it (changing the clocks from KMPH to MPH) it was out by about 25%:eek: I ripped that straight out.

unkel

We've done that one a few times before. See this. Any speedometer can legally only indicate anything between the real speed and the real speed + 10% of the real speed + 4km/h. Example: a real speed of 100km/h must be anything between 100km/h and 114km/h indicated on the speedo

Read the linky for more info. Provided the original circumference of tyre is used, there is a slight difference between brand new tyres and almost illegally worn tyres (about 2-4% if I remember my calculations correctly) and yes it presumes driving on a more or less horizontal (flat) road, although unless driving in a particulary mountainous area, this also makes very little difference

patrickc

unkel wrote: »

We've done that one a few times before. See this. Any speedometer can legally only indicate anything between the real speed and the real speed + 10% of the real speed + 4km/h. Example: a real speed of 100km/h must be anything between 100km/h and 114km/h indicated on the speedo

Read the linky for more info. Provided the original circumference of tyre is used, there is a slight difference between brand new tyres and almost illegally worn tyres (about 2-4% if I remember my calculations correctly) and yes it presumes driving on a more or less horizontal (flat) road, although unless driving in a particulary mountainous area, this also makes very little difference

sorry unkel, didnt realise it had been done then, lock away if ya like

always knew my speedo was out just wondered which was more accurate, but so many factors i know

Stephen

A decent sat nav will be able to read your altitude too. It can work this out if it can see 4 or more satellites.

unkel

No need to apologise! GPS wins over speedo any time

patrickc

unkel wrote: »

No need to apologise! GPS wins over speedo any time

i just find the boards search engine tedious, and hadnt noticed a thread specifically on it recently..

great more speed for me haha well imaginary speed..

unkel

patrickc wrote: »

great more speed for me haha well imaginary speed..

LOL

The fastest (imaginary) I've ever been driven in was a mini doing 120km/h really. Oh the excitement (nearly sh!tting myself) :rolleyes:

Twice that in my current car feels relaxed, safe and reasonable

patrickc

unkel wrote: »

LOL

The fastest (imaginary) I've ever been driven in was a mini doing 120km/h really. Oh the excitement (nearly sh!tting myself) :rolleyes:

Twice that in my current car feels relaxed, safe and reasonable

such excitement is right

whats your current car? i know youve many