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What is correct, Speedo or sat nav?
Comments
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Yeah well it's not as if I can edit it now either as Strider has quoted it....0
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Yeah well it's not as if I can edit it now either as Strider has quoted it....
I get blamed for everything
“I may not agree with you, but I will defend to the death your right to make an a** of yourself.”
<><><><><><><><><<><><><><><><><><><><><><> Don't forget to like and subscribe \/ \/ \/0 -
ScoobySnacks79 wrote: »The answer is that neither is likely to be entirely accurate.
. GPS is only accurate to a few dozen metres, and so can only give an average speed over a number of readings. For various reasons it is inherently slightly inaccurate.
Assuming that the speedo reads in a linear manner, then doubling the speed should double the difference between the speedo and the gps.
QUOTE]
I have two completely independent Satnavs [we call them GPS s] on my boat and their indicated positions agree within 2 metres most of the time ... actually .001 of a minute of latitude or longitude.0 -
What is correct, Speedo or...
Unless you look like a male model from a perfume advert a Speedo is never the correct choice.0 -
One of the main gripes about 50 limit "average speed" roadworks with lorry drivers is the fact that cars crawl through them at 45MPH or lower - not bad on a short stretch but on a 20+ mile stretch like the M1 around Nottingham recently, a real pain in the arras.
On cars, a speedo can overread up to 10%. Its accuracy is never ever checked.
On a HGV, the tacho can only overread up to 2.5% and its accuracy is checked and certified every 2 years and if incorrect is recalibrated. Therefore a lorry doing an indicated 50 is likely to be doing 49-50 whereas the car its stuck behind doing its indicated 50 can be doing 45MPH or less - very frustrating.0 -
They don't, but they have to make allowances for the different size tyres which could be fitted to the car.
It's not unusual for there to be a 2-3% difference in circumference from one wheel/tyre size to another for the same model car.
You can get 2% difference in diameter from a new tyre to a fully worn one.0 -
A car which underreads is not legal. The majority of speedometers do indeed overread, typically by 5-10%.
The cost of making a speedo that reads 100% correctly would be prohibitively expensive. Since an underreading speedo is illegal, what makes you think that manufacturers don't err on the side of caution?
I was countering the assumption that there was a set margin that manufacturers use to set their speedometers. The key thing is to never assume either way.The greater danger, for most of us, lies not in setting our aim too high and falling short; but in setting our aim too low and achieving our mark0 -
cyclonebri1 wrote: »But they do have to work to cost which means the speedo will never be as accurate as the satnav. To protect themselves from the claims culture they ensure the accuracy is always to the plus side to ensure they cannot be held liable if you get a ticket for 32 when your speedp readout is 30.;)
Your average common or garden satellite navigation system is even less accurate than your average speedometer.The greater danger, for most of us, lies not in setting our aim too high and falling short; but in setting our aim too low and achieving our mark0 -
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
Wow, that is quite a margin of error. :eek:The greater danger, for most of us, lies not in setting our aim too high and falling short; but in setting our aim too low and achieving our mark0 -
spugzbunny wrote: »My speedo is allways around 4mph faster than the SatNav at 70. So yes - in the 5-10% overread bracket.
But that is making the presumption that your satellite navigation is accurate.The greater danger, for most of us, lies not in setting our aim too high and falling short; but in setting our aim too low and achieving our mark0
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