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Could anyone advise please ? It seems, nowadays, that speedo accuracy is of ever increasing importance, especially when we hear of drivers being booked for, seemingly, small increases over a particular limit. Also, in my case, having converted my Japanese import's speedo face from KPH to MPH, I am getting a bit paranoid about it's accuracy. I can, of course, do a check by some arrangement wherebye I follow a driver who will indicate his speed but, with the knowledge that most speedometers are not very accurate anyway, this method has it's drawbacks. Does anyone know if the Police, or Dept of Transport, offer speedometer testing at any of their national centres? It is to be hoped that the police vehicle speedos are regularly checked, probably on an accurate chassis dynamometer but, is this facility available to the public ?
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DoT SVA centres check MPH speedo readings as part of the SVA test,but i dont think you could take your car along for just a speedo check.What car is it that you have changed the face on?I have seen many where just the face has been changed and because not enough care/attention was taken the reading is very optomistic,especially with the electricly powered units.Its allways better to fit an electronic converter or the mechanical speedos a small gearbox converter.Probably the best/easiest way to check your speedo is to compare it down the road with at least 2 different cars.The SVA check them upto 70 MPH,they are allowed to read over but never under.
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Best way to check a speedo is on the motorway. There are posts every 100m, so it's not too difficult to count the posts as they pass (they're even numbered so there's no mistake!) and time 2km at a few indicated speeds. Get an obliging passenger to help you so you don't fall off the road! Couple of minutes mental aritmetic will demonstrate what your actual speed is vs your indicated speed.
Did this on my BX as I was sure the speedo was reading way over - indeed it is, so I just ignore it now, and drive on the rev counter which is far more accurate.
Richard
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If you own, or have access to, a GPS this will give you acceptable readings. After all the system is accurate enough to be used to duff up crazed dictators, and may be again this year!
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I have checked several vehicles, mostly Peugeots, using the Mway 100-metre markers. On a longish journey this can be done using the trip recorder over a measured 30 or 40 km. All cars have recorded high by ½ to 2 percent (distance) or 1 to 4 percent (speed). All 205s show at the top of this range, 306s are closer to the truth.
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John,
I would suggest asking a traffic occifer to point you in the direction of some measured mile markers.
Its easier than counting motorway posts, and if you time yourself over the distance at varying speeds then you can draw a calibration curve to get the accuracy over the whole range from 30 to 70 Thus you can then happily blat along, assuming its safe at an indicated 74 say, knowing that it is a true 70.
In the absence of a guidance from a proper b-i-b if you know where your local traffic unit is based, or maybe force HQ you should find some markers on measured miles handy for outgoing and incoming patrols.
Typically you find that the markers are the black and white road edge marker posts complete with red reflector on top, and there may be a white paint line painted out perpendicularly out from the kerb at start and finish. Some distances are 1 mile some 0.5.
Once you know what to look for then they become easier to spot.
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What I believe is a measured mile on the M4 near J 14 uses a small circular yellow sign at the start, with every quarter mile marked by a similar sign with an additional quadrant changed to red.
Regards
John S
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Top Tip:
How about get yourself photo snapped by a speed camera and then compare your speedo reading with the photo that comes through the door!
S.
(Seriously though, easiest is to compare yourself with other cars by driving alongside on a dual carriageway or motorway when quiet and with a colleague. Also the timing method (lascar?) between posts or countdown junction markers could be used.
You could also time yourself against your odometer/tachometer display and calculate an average speed from it?
S.
_____________________________________
SVPworld (incorporating PSRworld)
www.svpworld.com
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Thanks to all for the helpful replies. Yes, the GPS method sounds good and I have already put out the feelers among my gadget loving friends.
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If you live near Grantham I could help out with a GPS.
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I have worked on a Motorway and can say that the marker posts are generally always 15% out. (Yes I measured them.) Although over a long stretch they should average out.
I would recon that the sliproad countdown signs are the same.
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Many thanks indeed AS. In fact, I do live just across the border (Leics) and know your lovely town very well. However, when I mentioned it to my London based Son, who will be visiting next weekend, the reply was "Why didn't you say ? I use my GPS device all the time for my regular SIXTY mile cycle rides ".
He will be bringing the GPS unit with him but, thanks again for your kind offer of help.
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In Hertfordshire there are pairs of square solid white markings about 60cmx60cm on various roads (set in the centre of the lane). I have always believed that these were for police use for calibration checking. I do not know the distance apart. Can anybody confirm use and distance?
pmh (was peter)
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pmh
these are reference points for vascar/provida and similar.
The true story, albeit somewhat tongue in cheek, of how these came about in one force is in the following post.
www.honestjohn.co.uk/forum/post/index.htm?t=1575&m...e
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"when we hear of drivers being booked for, seemingly, small increases over a particular limit"
No we don't.
An oft repeated urban myth.
Time after time this nonsense gets repeated as "fact".
What are Gatsos set at?
In my county at 39 in 30 limits.
To answer your question, I have done the GPS bit with 4 cars - the results were between 3 and 6% fast at 60mph.
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"No we don't."
Yes we do. Not all "bookings" are done via Gatso's and many drivers DO get booked for much smaller percentage increases over the speed limit.
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Yep Essex plod have the "37 club" whereby 37 mph gets you a version of traffic school.
My next door neighbour has a NIP for 34mph in a 30 issued manually courtesy of Cheshire's finest galls a bit when local housebreaking stats are at 10% clearup.
as ever
Mark
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Sorry not 34 but 35 although he insists it was 34, it does actually say 35 on the form.
as ever
Mark
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Now that REALLY is the "nonsense" mentioned by a previous contributor and, sadly, it REALLY is a fact.
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ive checked a couple with a gps and seem to be and seem to be 3 0r 4 mph faster then the gps
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Best thing to do to make sure your vehicle gives an acurate reading, is to drive a Maestro!
Within their own checks, the police found these vehicles to give the most precise readings, from ALL vehicles within their fleets!
Mark
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I knew there had to be a positive feature somewhere!
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I thought the most accurate were Citroens. Can't speak for C5's ec but the Xantias (Xantiae?) and BX I've checked have been cock on. (are we allowed to say that????/ clicks preview button....hmmmm yes it appears)
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Hi,
I recently i.e. Tuesday tested a Vauxual Astra Estate 3000miles on the clock for speedo accuracy using a serious chunk of Trimple Professional GPS and roof Antenna. This was on an airfield runway so a steiaght line was not a problem at 60mph true speed the speedo read a touch under 63mph and at 30 mph the speedo read 31/31.5.
Same car on the motorway straight section using 2km markers and a little maths and the figures were almost identical. Using the motorway if accurate enough but holding your speed is the difficult bit if other traffic around and at noght you can not read the markers. Suggest Sunday mornings early on.
My Volvo electronic speedo is spot on at 60 and lass than 1 mile high at 30.
VW Golf spot on at 30 1 mile high at 60 and 2 miles high at 90. Runway test of course.
Peter
Peter
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Sorry about the typos there. Trimble, straight, night, less
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>When we hear of drivers being booked for, seemingly, small >increases over a particular limit"
>
>No we don't.
>
>An oft repeated urban myth.
I think this varys from police force to police force. I was on the M40 the other day and noticed a marked police Vauxhall Omega behind me. Looked at my speedo and was doing 85mph.
I just moved over into the middle lane and he went passed.
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