View Full Version : Sat nav or car most reliable
Which one's MPH should I trust.
On my way into work this morning in my new car I noticed that when the car odometer read 62 the sat nav read 58.
i would've been happy to accept that sat nav's have superior technology and trust that reading more, however...
crawling along in a queue the car read 3 MPH and the Sat Nav said 0MPH!
Which one do I believe?
I always believe my car they do say there can be a 10% difference in speed reading, i got a gps camera device which shows me doin 2 mph less than what my car says
svdemon
30-03-09, 11:08 AM
I would tend to believe the sat nav more, perhaps it doesn't bother reading under 5/10 mph?
Ceri JC
30-03-09, 11:13 AM
On a straight section of road the GPS will be more accurate, IMO. They don't seem to overread to the same extent as in car ones (if at all).
richie95
30-03-09, 11:16 AM
gps... has a few miles under car... i heard somewhere that the speedo on cars are out as a deterent to speeding, by a percentage, so you think your doing 70 its actually 65... maybe just another motorised myth...
jimmy__riddle
30-03-09, 11:32 AM
gps... has a few miles under car... i heard somewhere that the speedo on cars are out as a deterent to speeding, by a percentage, so you think your doing 70 its actually 65... maybe just another motorised myth...
i dont think its a deterrent to speeding, but more or a liability thing for the manufacturer. it you went past a speed camera at an indicated 30 and got a ticket cos you was doing 32 you would be a little annoyed. they make them over read so that doesnt happen, and they allow for manufacturing tollerances.
As for GPS, do they take vertical change into consideration? i.e. actual distance travelled or distance in X Y only?
punyXpress
30-03-09, 01:28 PM
Ever since my Garmin claimed I was walking at 19 mph I've had my doubts.
I'm so slow I'm into third by then !
Oh I was hoping for some knowledge here.
i have an opinion lol
punyXpress
30-03-09, 08:43 PM
A..B..C.................D..E..F
Satnav has a ( small ) margin of error
To measure B to E above, you would be OK with A to D, B to E, & C To F
BUT A to F would read high & give fast reading & C to D the opposite.
A..B..C.................D..E..F
Satnav has a ( small ) margin of error
To measure B to E above, you would be OK with A to D, B to E, & C To F
BUT A to F would read high & give fast reading & C to D the opposite.
Ow that hurts!
Vehicle manufacturers are required by regulation to have speedometers which "do not under-read", so by definition all vehicle speedos will over-read by a small amount.
There's no hard and fast rule by how much, but somewhere up to 10% is possible, often 10% at low speed (e.g. 33 at a true 30), a bit less at higher speeds (e.g. 75 at a true 70).
There is no regulatory reason for sat-nav to read under or over, they'll be out only by technical limitations.
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