I have been told that, your standard, run of the mill, high street Sat Nav speed indicator reads 10% lower than your actual/realtime speed. Is this true? Or is it 100% correct to the acutal car speed?

On my Navman, it reads approx 10% lower in my 300, my "dirt bag" Citreon, and the wife's Golf.

 

Al.

Satnav is about as accurate as you can get. Most speedometers will read up to 10% out, especially at higher speeds.

 

My shitroen overreads at low-mid speeds and underreads at highspeed

Is it not true that the time taken from the Satnav to the satellite, back to the Satnav to indicate the car speed, accounts for the 10% deflection in speed error? I don't know, maybe i am getting a bit old, and not staying in touch!!!!

 

Al.

SatNavs are passive .... they only receive the GPS Signals which travel at the speed of light (or very close to it) so the only time you are losing is the time to process the data and display it....

Not to sure about the ones for road use, but the one on my boat ,is more acurate as it has know interferance ie buildings and metal /out at sea

So, to sum up, GPS speed ratings are as close to real time speed as you can get. Is that correct? If so, i think i need to adjust my potentiometers on my 300, to get a good dial speed reading.

 

Al.

Would be best to get them calabrated buy an expert !

All speedo's that I have come across read around 10% slower

I can do them myself, 2 little screws under the surround for the guages, and i have put 2 holes so to slip in a small screwdriver and adjust as i drive, with a matey to hold the wheel!!

 

Al.

All speedo's that I have come across read around 10% slower

 

Slower than a Satnav reading?

 

Al.

The sat nav should be as close to your real speed as you can get. If it's different to your speedo, then as everyone has said, your speedo is wrong. It is normal for the speedo to read faster than you are actually travelling.

 

On my ZX the speedo is between 3 and 7 mph out depending on how fast I'm driving. Between 70 and 100 is furthest out; but over 100 (not on the public roads of course) it seems to regain some accuracy.

 

On my SLK the speedo is never more than 3 mph out - even at 155 mph (autobahn of course).

 

On the Rav-4 it is almost 10% out once over 70 mph - ie at true 80 mph the speedo reads 87.

 

There you have it - most car speedos over-read. So when a spotty chav in the pub says his Saxo does 130 mph, chances are he's not actually been over 110;)

 

Richard:smw:

Would be best to get them calabrated buy an expert !

 

why how much are they????

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

sorry mate ime standing in for funky:tongue::tongue:

Dont know , bit cheaper than pionts and a fine though,

Dont know , bit cheaper than pionts and a fine though,

 

:rofl::rofl::rofl:classic

Slower than a Satnav reading?

 

Al.

 

Sorry, faster, I can not multi task !!

 

I think it must be something the car manufacturers do on purpose, not sure on the reason other than a comfort zone, motorbike speedos are just as bad if not worse.

SatNavs are passive .... they only receive the GPS Signals which travel at the speed of light (or very close to it) so the only time you are losing is the time to process the data and display it....

 

So this could be the 10% reduction in speed display?

 

al.

I always follow satnav as accurate speed reading, as in my M3 the speedo is about bang on, about a needles width out at 70mph and not much further out at 100mph, maybe 99 on the satnav at 100 on the clock.

By contrast my van is reading about 110 on the speedo @ 100 on the satnav

So this could be the 10% reduction in speed display?

 

al.

 

There is no 10% reduction. At a constant speed they are extremely accuate, unlike a car speedometer. The innaccuracy your seeing is in the speedo, not the satnav.

Most speedos will show a slightly higher speed than is real but this is exaggerated because most Z's have had larger wheels fitted too which throws the speedo out even further.

My satnav reads faster, 65 on the clock and 70 on the nav. BUT the indicated speed on the satnav means nothing in a court of law.

My speedo has always been spot on since i fitted the 19" alloys on :)

There is no 10% reduction. At a constant speed they are extremely accuate, unlike a car speedometer. The innaccuracy your seeing is in the speedo, not the satnav.

 

So there is no time taken at all for the satnav to pick up a signal, transfer that signal to a satellite, reply that information back to the satnav, then satnav to translate this information into time related distance travelled. I am a bit sceptical matey, even if it would account to milliseconds, it cannot be that accurate.

 

Al.

There is a delay when accelerating and braking, but at a constant speed they are very accurate.

 

GPS manufacurers say 0.1mph accuracy. Speedometers are given a 10% accuracy.

There is a delay when accelerating and braking, but at a constant speed they are very accurate.

 

GPS manufacurers say 0.1mph accuracy. Speedometers are given a 10% accuracy.

 

Spot on....

 

Richard:cool:

the speedo on my jdm on 17" rims and stock suspension read the same as my tomtom, it's the only car I've ever owned that has had an accurate reading from the speedo.

There is a delay when accelerating and braking, but at a constant speed they are very accurate.

 

GPS manufacurers say 0.1mph accuracy. Speedometers are given a 10% accuracy.

 

Sorry matey, 0.1 MPH accuracy for GPS speed indicators!?!?

 

If you have a link that backs this up then i will eat humble pie!!

 

Al.

 

Oh BTW.............

 

THIS MY 1000th POST WWHHOOOO!!!!!