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UK Caravanning (uk.rec.caravanning) A forum for the discussion of caravanning undertaken by residents of the United Kingdom, whether in the UK or abroad. It encourages the interchange of views on the merits of models of caravan, makes of tow car, accessories, caravan sites, caravan clubs, and other related topics. The term caravan is to include trailer vans, motor caravans and trailer tents.

GPS speed



 
 
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  #1 (permalink)  
Old May 16th 05, 10:29 PM posted to uk.rec.caravanning
Colin Williams
external usenet poster
 
Posts: 8
Default GPS speed

Hi,
All three of my new cars over the years never agree with the GPS speed. They
all read faster than the GPS speed. Which is more accurate, as speed
cameras are also measuring a few MPH if over the top.?
Thanks you

Colin Williams


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  #2 (permalink)  
Old May 17th 05, 05:08 AM posted to uk.rec.caravanning
David
external usenet poster
 
Posts: 1,622
Default GPS speed


"Colin Williams" wrote in message
...
Hi,
All three of my new cars over the years never agree with the GPS speed.

They
all read faster than the GPS speed. Which is more accurate, as speed
cameras are also measuring a few MPH if over the top.?


Mine is like that.
Car 30mph
GPS 27mph

Cat 70mph
GPS 67mph


--
Regards,
David

Please reply to News Group.


  #3 (permalink)  
Old May 17th 05, 05:08 AM posted to uk.rec.caravanning
David
external usenet poster
 
Posts: 1,622
Default GPS speed


"Colin Williams" wrote in message
...
Hi,
All three of my new cars over the years never agree with the GPS speed.

They
all read faster than the GPS speed. Which is more accurate, as speed
cameras are also measuring a few MPH if over the top.?


Mine is like that.
Car 30mph
GPS 27mph

Cat 70mph
GPS 67mph


--
Regards,
David

Please reply to News Group.


  #4 (permalink)  
Old May 17th 05, 05:21 AM posted to uk.rec.caravanning
Sam1953
external usenet poster
 
Posts: 4
Default GPS speed

The GPS speed is likely to be more accurate, but it is not wise to take
a chance, and the police will not accept the excuse that you were using
your GPS as a speedometer.

My GPS also reads a slower speed than the car speedo, by around 10%
consistently up to and including speeds over 120mph (done in Germany of
course).

  #5 (permalink)  
Old May 17th 05, 05:21 AM posted to uk.rec.caravanning
Sam1953
external usenet poster
 
Posts: 4
Default GPS speed

The GPS speed is likely to be more accurate, but it is not wise to take
a chance, and the police will not accept the excuse that you were using
your GPS as a speedometer.

My GPS also reads a slower speed than the car speedo, by around 10%
consistently up to and including speeds over 120mph (done in Germany of
course).

  #6 (permalink)  
Old May 17th 05, 06:58 AM posted to uk.rec.caravanning
Dave Fawthrop
external usenet poster
 
Posts: 1,941
Default GPS speed

On Mon, 16 May 2005 22:29:10 GMT, "Colin Williams"
wrote:

| Hi,
| All three of my new cars over the years never agree with the GPS speed. They
| all read faster than the GPS speed. Which is more accurate, as speed
| cameras are also measuring a few MPH if over the top.?
| Thanks you

Car speedometers are notoriously inaccurate and read less than the real
speed as you say. I have calibrated my car speedometer against the GPS
which I believe to be more accurate. I now have an extra 3-5mph if I
need it.

--
Dave Fawthrop dave hyphenologist co uk
On any Usenet newsgroup, *truth* is defined by the person or
group who shout longest and loudest.
It is not related to any reality. :-(
  #7 (permalink)  
Old May 17th 05, 06:58 AM posted to uk.rec.caravanning
Dave Fawthrop
external usenet poster
 
Posts: 1,941
Default GPS speed

On Mon, 16 May 2005 22:29:10 GMT, "Colin Williams"
wrote:

| Hi,
| All three of my new cars over the years never agree with the GPS speed. They
| all read faster than the GPS speed. Which is more accurate, as speed
| cameras are also measuring a few MPH if over the top.?
| Thanks you

Car speedometers are notoriously inaccurate and read less than the real
speed as you say. I have calibrated my car speedometer against the GPS
which I believe to be more accurate. I now have an extra 3-5mph if I
need it.

--
Dave Fawthrop dave hyphenologist co uk
On any Usenet newsgroup, *truth* is defined by the person or
group who shout longest and loudest.
It is not related to any reality. :-(
  #8 (permalink)  
Old May 17th 05, 07:31 AM posted to uk.rec.caravanning
Andy R
external usenet poster
 
Posts: 821
Default GPS speed


"Dave Fawthrop" wrote in message
...
On Mon, 16 May 2005 22:29:10 GMT, "Colin Williams"
wrote:

| Hi,
| All three of my new cars over the years never agree with the GPS speed.
They
| all read faster than the GPS speed. Which is more accurate, as speed
| cameras are also measuring a few MPH if over the top.?
| Thanks you

Car speedometers are notoriously inaccurate and read less than the real
speed as you say.

IIRC to meet approval standards vehicle speedos can over-read by up to 10%
but cannot under-read.

I have calibrated my car speedometer against the GPS
which I believe to be more accurate. I now have an extra 3-5mph if I
need it.

The manufacturers set the speedos to over-read to allow for errors caused by
temperature, humidity, wear and the fact that it's difficult to get a cheap
guage to read accurately throughout its entire range and for a life of maybe
10 years or more. Consider also that your GPS is only as accurate as your
speed control over the sampling period at each different speed and the road
you took the sample on must have been flat with no bends.

Rgds

Andy R


  #9 (permalink)  
Old May 17th 05, 07:31 AM posted to uk.rec.caravanning
Andy R
external usenet poster
 
Posts: 821
Default GPS speed


"Dave Fawthrop" wrote in message
...
On Mon, 16 May 2005 22:29:10 GMT, "Colin Williams"
wrote:

| Hi,
| All three of my new cars over the years never agree with the GPS speed.
They
| all read faster than the GPS speed. Which is more accurate, as speed
| cameras are also measuring a few MPH if over the top.?
| Thanks you

Car speedometers are notoriously inaccurate and read less than the real
speed as you say.

IIRC to meet approval standards vehicle speedos can over-read by up to 10%
but cannot under-read.

I have calibrated my car speedometer against the GPS
which I believe to be more accurate. I now have an extra 3-5mph if I
need it.

The manufacturers set the speedos to over-read to allow for errors caused by
temperature, humidity, wear and the fact that it's difficult to get a cheap
guage to read accurately throughout its entire range and for a life of maybe
10 years or more. Consider also that your GPS is only as accurate as your
speed control over the sampling period at each different speed and the road
you took the sample on must have been flat with no bends.

Rgds

Andy R


  #10 (permalink)  
Old May 17th 05, 09:46 AM posted to uk.rec.caravanning
Harpic
external usenet poster
 
Posts: 66
Default GPS speed


"Colin Williams" wrote in message
...
Hi,
All three of my new cars over the years never agree with the GPS speed.
They all read faster than the GPS speed. Which is more accurate, as speed
cameras are also measuring a few MPH if over the top.?
Thanks you

Colin Williams


Speedometers can never be accurate. they work by counting the number of
revolutions of the final drive from the gearbox.

Remember - as your tyres wear their diameter and therefore their
circumference reduce, resulting in less distance travelled per revolution of
the road wheel, which then requires more revolutions to travel each mile.

This difference can be as much as 3% so this will make the speedo vary by
3% throughout the life of the tyre.

As a rough Guide

15 Inch wheels
New tyre Diameter 22 inch Circumference 69.1 inches Revs per mile 917
Assuming 6mm difference in tread depth
Worn Tyre diameter 21.5 in Circumference 67.5 inches Revs per mile 938

100 x (938-917) / 938 = 2.33%





 



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