I went through a speed camera in a 70 limit the other day, my speedo said 84 but my sat nav showed 77, which do you think will be correct?
Thanks
2007-03-08 02:17:08 · 16 answers · asked by malc 1 in Cars & Transportation ➔ Safety
Think - you are comparing millions of pounds worth of global satellite technology with a £30 mass produced instrument.
The car speedo is a notoriously inaccurate instrument, even changing tyre/wheel sizes can adversely affect the instrument reading.
My car has factory fitted low profile tyres, and like yours the speedo reads about 5 mph high when compared with satnav at 70 mph - you only have to work out the rolling circumferance of the tyre to see the reason why.
Lower profile tyres will turn at the same rpm for a given indicated road speed but as they cover less actual distance per revolution your true speed will be lower.
The sat nav unit will give a reading of your true ground speed, and if you don't believe me, all you doubters, how do you think the sat nav can calculate a 'time to arrival' so accurately?
2007-03-11 22:36:00 · answer #1 · answered by rookethorne 6 · 0⤊ 0⤋
Most modern cars overclock you actual speed, if you have a trip computer and sat nav you can test both of them for an actual reading.
I have a Mondeo and the computer speed is the same as my sat nav, If I'm doing 80 my sat nav and computer both read 76.
In either case even allowing the mandatory 10 per cent, I would hazard a guess you will be receiving a letter with a fine and 3 points.
Sorry.
2007-03-08 02:23:36 · answer #2 · answered by Tooly 3 · 1⤊ 0⤋
I am sorry but you are all wrong when you say your speedo. A car's speedometer gives an indication of speed which will always be slow unless the speedo is faulty. It is a mechanical device, (even the digital ones), which can be fooled just by your tyres being under or over inflated. A sat nav calculates the speed from a distance/ time calculation from fixed satellites. Even if a sat nav is only accurate to 30', the accuracy of the speed indication is about 99%.
2007-03-08 02:37:06 · answer #3 · answered by Anonymous · 2⤊ 2⤋
I think it depends on how accuratlly your sat nav is working at the time, but I would tend to believe that over the car speedo. I think they read a bit high to impress you with the speed of the car. I recently had a Renault Kangoo 1.4 deisel wound up to 178KPH, according to my GPS, downhill on an autobahn in Germany. The speedo showed around 190KPH a phyical impossiblity of this car., then again, I thought 178 was!
2007-03-08 02:24:30 · answer #4 · answered by Reg Tedious 4 · 0⤊ 0⤋
You car speedo. Non-military grade Sat Nav systems are not as accurate and may be off by over 30 feet.
2007-03-08 02:21:16 · answer #5 · answered by Tom C 3 · 2⤊ 1⤋
your sat -nav ,was being lenient
with that = 7mph =excess of permitted speed limit .
your speedo is the most accurate
you were doing ,=14mph= in excess
of the permitted speed limit
you will be docked points, off your driving licence and possibly a *ban on driving * for some time .
With endorsements on your license,
your insurance company, will raise your premiums
as night follows day . .
Sorry , you will have 'the book thrown at you '.
So Lucky ,you did not kill anybody, or get hurt yourself
Speed KILLS
>^,,^<
2007-03-09 00:15:51 · answer #6 · answered by sweet-cookie 6 · 1⤊ 1⤋
You speedo is going to be more accurate by far.
The electrical and maechanical relationship for your vehicles tires and drivetrain gearing are pretty much an exact calculation. It's also a direct calculation.
Your navigation system is measuring distance from a satelite about 10 miles away. It's going to be close, but it's not going to be exact. You've also go transmission delay times to deal with. When it sends you a speed measurement, it's actually sending you the speed you were moving a few seconds ago, not the speed you are travelling at right now.
Trust your navigation system for directions and location. Don't trust it for speed calculations. Your speedo is going to be much more accurate.
2007-03-08 02:28:30 · answer #7 · answered by Lemar J 6 · 2⤊ 2⤋
it has to be Sat Nav. Speedo speed varies on whether you have new tyres or old tyres on your car.
The speedo counts the revolutions and uses this in a calculation including the circumference of the tyre. This will be longer for new tyres and hence will give a different reading.
2007-03-08 03:00:29 · answer #8 · answered by Mark J 5 · 2⤊ 2⤋
Perhaps cars shouldn't have sat nav or speedos, but be fitted with speed cameras...........
2007-03-08 06:48:34 · answer #9 · answered by ? 3 · 0⤊ 0⤋
If your sat nav is not wired into a vehicle speed signal then its depending on gps to estimate your speed.In this case your vehicle speedo is the more reliable
2007-03-08 02:21:23 · answer #10 · answered by havanadig 6 · 2⤊ 1⤋