Sat navs can't take inclines/declines into account, the speedo does, so best to rely on it and assume it's no more than a few mph over.
Or, perish the thought, drive to the speedo and travel a few mph under.
Speed limits are not a minimum or a target, they are a maximum.
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Accordig to my satnav my Golf overreads by 3 mph at any speed.
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'According to my satnav my Golf overreads by 3 mph at any speed'.
Interesting - my Astra does exactly the same. Not the fixed percentage error you'd expect.
JS
Edited by John S on 19/05/2008 at 21:02
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Speed limits are not a minimum or a target they are a maximum.
Very often an absurdly low blanket limit set without real thought as to its appropriateness or otherwise.
Perish the thought indeed. Five or ten over is nearly always quite all right, best five when actually passing a speed camera. Naturally any resulting carnage is entirely the driver's responsibility, so it pays to drive at an appropriate speed even on the very rare occasions when this is below the speed limit.
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My favourite game, on the A69 at Low Row there are 2 speed cameras in quick succession, both on straights, though one is a bit dangerous as right by a fuel station.
For some reason the trucks drop to 40mph so, if safe, I overtake in the camera zone keeping below 60 mph. Amazed looks from everyone else.
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Isn't 40mph the speed limit for HGVs on a single carriageway road? That'd explain the slowing down...;-)
Peter
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You are absolutely correct, Peter, hence the great opportunity, if safe, to get past them before they speed up again to 55mph or thereabouts.
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Extract from www.speed-trap.co.uk :-
"ACPO Guidelines on speeding, and the UK law regarding prosecution.
Vehicle construction and use regulations require a vehicle speedometer accuracy to be in the range of -0->+10%. The implications are that it must never under-read - for obvious reasons - but may over-read. As the cost of manufacturing a speedometer with -0% error would be very costly they all over-read by a few percent without exception. Even if speed is measured correctly the display may not be accurate, so a speedometer error is allowed. Because of this, the Association of Chief Police Officers (ACPO) have an official formula for calculating a speeding offence. It allows a leeway of 10% plus 2mph. In reality, most speed traps are triggered at higher speeds than this because if they were set bang-on those guidelines, the sheer amount of paperwork generated would overrun the police speeding departments."
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(ACPO) have an official formula for calculating a speeding offence. It allows a leeway of 10% plus 2mph. >>
Wasn't someone posting a couple of weeks ago having been flashed at 34 in a 30 limit and taken a safer driving course?
Or am I beginning to hallucinate threads on this forum?
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ACPO guidelines are only advice...if someone in a Safety Camera Partnership wanted to set a low limit, there's nothing stopping them
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Our Subaru Forester II 2.0x 2003, 76 on speedo = 70 on TomTom
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My experience of many cars confirms that they nearly all over read by the permitted 10%. Obviously this does help to avoid exceeding speed limits, which I do not regard as optional, but most drivers could confirm their own speedo's reading if they followed the average modern HGV on the Motorway, where, subject to much tighter tolerences, they will be doing exactly 56 mph. I will bet your car's speedo will be showing around 60/62. that 4 or 5 mph difference is the 10% (or thereabouts) your speedo is fast.
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My Hyundai and my VW speedos do/did not overread by as much as 10% but seemed to have a 3/4 mph error at most speeds. According to the Road Angel anyway.
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My various Vauxhalls, well at least those I've checked against motorway markers, have over-read by close to 10%, but my current lovely green Vectra is more or less spot on. Another equally sad co-worker says his Vectra is much the same.
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My current car over reads by 2 mph consistantly across the legal range with nearly new tyres.
My previous car speedo was very inaccurate, at least +10% so I had the speedo recalbrated by a garage who claimed (rightly) that it would be within 3% of actual speed. It was then accurate to +/- 1 mph from 30-80 mph and over read by 3 or 4 mph at 20-25 mph and below 20 mph next to useless.
Edited by Marc FourSix on 20/05/2008 at 19:21
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I have found over the last few years that spedos are getting more accurate,The digital readout ones tend to be nearly spot on and the analoge dial ones vary usually about 5 % high.
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My A3 is only 2mph high at 70 and 1mph high at 30, according to my sat nav.
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