What is correct, Speedo or sat nav?

adouglasmhor

From wiki not the best source but short notice etc.

GPS devices are positional speedometers, based on how far the receiver has moved since the last measurement. Its speed calculations are not subject to the same sources of error as the vehicle's speedometer (wheel size, transmission/drive ratios). Instead, the GPS's positional accuracy, and therefore the accuracy of its calculated speed, is dependent on the satellite signal quality at the time. Speed calculations will be more accurate at higher speeds, when the ratio of positional error to positional change is lower. The GPS software may also use a moving average calculation to reduce error.

As mentioned in the satnav article, GPS data has been used to overturn a speeding ticket; the GPS logs showed the defendant traveling below the speed limit when they were ticketed. That the data came from a GPS device was likely less important than the fact that it was logged; logs from the vehicle's speedometer could likely have been used instead, had they existed.

Lum

adouglasmhor wrote: »

Missing the point there a bit Birkee, yes you need to have an operational speedo, guess what, your sat nav counts, one of my motorcycles had a radar speedometer that counted too, no one is saying you don't legally need a speedo, just that is not the speed reading they will use to prosecute if you exceed the limits.

Satnav doesn't count. For one it doesn't work on a dyno, second it doesn't work in tunnels or certain city centres.

I looked into this when I was converting my car (Japanese Import) before registering it in the UK as it's a requirement to have a speedo that reads in MPH. The rules explicitly exclude using GPS devices for this. Ended up going with a Defi VSD heads up display thingie hooked up to the speed wire going into the car's ECU. It's also interesting that the Defi is more accurate than the car's actual speedo despite both using the same source. Guess the arrow doesn't quite line up.

adouglasmhor

You can get satnav in MPH and you don't need to be on a dyno. The radar one on my bike was not on a dyno, I did point out it may not work in tunnels though.

adouglasmhor

Found this

Regulation 35 Road Vehicles (Construction and Use) Regulations 1986 states that every motor vehicle shall be fitted with a speedometer except:

a vehicle having a maximum speed not exceeding 25 m.p.h.,
a vehicle which, at all times, is unlawful to drive at more than 25 m.p.h.,
an agricultural motor vehicle driven at not more than 20 m.p.h.,
a motor cycle not exceeding 100cc first used before 1st April 1984,
an invalid carriage first used before 1st April 1984,
a works truck first used before 1st April 1984,
any vehicle first used before 1st October 1937,
a vehicle fitted with an approved tachograph which is required or not.

Vehicles first used on or after 1st April 1984 the speedometer should be capable of indicating the speed in miles per hour and kilometres per hour. Vehicles may instead comply with EC Regulation (Community Directive) 97/39 or ECE Reg 39.
These directives stipulate the markings, graduations of the speedometer and refer to 75/443/EEC which specifies the tolerances.

The indicated speed must never be less than the true speed (it must read exact or high) and between 40km/h and 120km/h the error must not exceed 10% + 2.5 m.p.h. high (true speed/10 + 4kph).
This means at a true speed of 25mph or 40km/h the speedometer may read 40/10+4 = 8km/h or 5mph high = 30mph indicated.

Maintenance

Regulation 36 Road Vehicles (Construction and Use) Regulations 1986 states that the speedometer fitted to a vehicle must be kept free from any obstruction which may prevent it from being easily read and shall at all times it is used on a road be maintained in good working order except if:

the speedometer became defective during the journey being undertaken, or
steps have been taken to have the defect remedied by replacement or repair with all reasonable expedition, or
the vehicle is fitted with an approved tachograph which is required to be fitted under the Community Recording Equipment Regulation (offence is under that regulation).

Some top of the range (usualy only built in) built in sat-navs as well as having GPS input, are also fed with gyroscopic information and a speedo sensor.

cyclonebri1

jase1 wrote: »

I have quite high level academic and professional qualifications, and a relatively well paid job (c80k/year) /QUOTE]


And I believe you, :rotfl:

cyclonebri1

birkee wrote: »

Let them identify you as having a non working speedo then.

United Kingdom

The amended Road Vehicles (Construction and Use) Regulations 1986 permits the use of speedometers that meet either the requirements of EC Council Directive 75/443 (as amended by Directive 97/39) or UNECE Regulation 39.[11]
The Motor Vehicles (Approval) Regulations 2001[12] permits single vehicles to be approved. As with the UNECE regulation and the EC Directives, the speedometer must never show an indicated speed less than the actual speed. However it differs slightly from them in specifying that for all actual speeds between 25 mph and 70 mph (or the vehicles' maximum speed if it is lower than this), the indicated speed must not exceed 110% of the actual speed, plus 6.25 mph.
For example, if the vehicle is actually travelling at 50 mph, the speedometer must not show more than 61.25 mph or less than 50 mph

Point missed Birkee
Speeding is speeding, the feds have calibrated kit you/we don't end of

jase1

cyclonebri1 wrote: »

And I believe you, :rotfl:

Don't care if you do or not

I regretted posting that as soon as I hit the enter key to be honest. Really none of anyone else's business what I or anyone else earns.

alleycat`

cyclonebri1 wrote: »

Point missed Birkee
Speeding is speeding, the feds have calibrated kit you/we don't end of

When they bother to get them calibrated...

Lum

adouglasmhor wrote: »

You can get satnav in MPH and you don't need to be on a dyno. The radar one on my bike was not on a dyno, I did point out it may not work in tunnels though.

I know you can get in them in MPH. I only brought up KPH vs MPH because that was the situation that caused me to look up the regulations in the first place (the speedo on my car only has KPH, no MPH markings at all)

The lag and the fact that they dont work in tunnels automatically puts them in foul of said regulations as it means they underread during acceleration and can overread by more than 10%+6.25 during braking.

cyclonebri1

jase1 wrote: »

Don't care if you do or not

I regretted posting that as soon as I hit the enter key to be honest. Really none of anyone else's business what I or anyone else earns.

And therefore totally irrelvant to this or any other thread??

Which really is then point. Post your qualifications or status or even situation if it gives creedance to your views, but earnings??:rotfl:

Sorry, many burglars can beat your quoted figures.

Jase, didn't mean that to be personal but my dicks bigge,,,,,,,,,,,,,,,,,,,,,,,,,;)