car question

[sheelinside]

i have recently bought a GPS for the car, and i notice as i drive that it is consistenly reading about 6 or 7km per hour lower than the speedometer.
anyone else notice something like this?
which one would you go by?

[Gaaman]

i have recently bought a GPS for the car, and i notice as i drive that it is consistenly reading about 6 or 7km per hour lower than the speedometer.
anyone else notice something like this?
which one would you go by?

Is this an actual serious question?

[sheelinside]

actually yes.
it does seem like a silly question- first let me explain.
unless i am sitting about 5km over the speed limit everyone is flying passed me
also the GPS is 100% accurate with distances, and it changes in line with the car mileage clock

[mylestheslasher]

I think there is a logical explanation for this. The GPS is giving your actual speed. The Car manufacturers normally tune your speedometer on the safe side to allow for calibration and instrument tolerance issues. So basically, the car speedometer has a factor of safety built in.

[Bud Wiser]

I suggest you read all of this on the link below and come back to us in about a years time when you have it all condensed. It depends on whether the unit was made in america using their mile measurements or Irish Miles. Basicly I think you need to transfer your speed on the GPS into inches and then divide by .99990 inches and add it to the original speed but do not try it while smoking a cigarette, being on your mobile and driving at the same time.  When you find out will you tell them assholes with the new GPS speed traps that are issuing summonses for people being 4Km over the 50km limit that they need to get a big calculator and throw it in the back of their unnmarked vans as well.

http://en.wikipedia.org/wiki/Mile

[Maiden1]

The speedometer in your car is only an approximation.  It is using the circumference of your tyre and the no of revolutions of the wheel to work out your speed.  If your tyres are a bit softer or the thread is slightly more worn than average then the distance the car travels in 1 revolution will be slightly less.  You can't use your speedometer as an accurate assessment of your speed which is why the police are supposed to allow 10% (allegedly) when using the speed traps.