Ash_EP3
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Registered: 15th May 07
Location: Melksham, Wiltshire
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Firstly let me explain I downloaded an app on my phone (speedview) which using GPS tells me how fast I am going - the app is free and I wouldn't have thought for 1 minute it was 100% accurate...
As I've heard a lot on forums that car speedo's are out so I thought I'd test my speedo and I can confirm it was 5% out throughout most of the range 30+....
30 on speedo = 28/29 on gps
31/32 on speedo = 30 on gps
63 on speedo = 60 gps...
130 on speedo = 123 on gps 
So roughly 5% ish out throughout the range (not too bad for a 7 year old car...)
Tested this on my bro's (aerox-lad) corsa the other day and that was 10% out.. (66 on speedo = 60 on GPS)
Question is why are car speedo's out so much (is it a calibration issue?)?
That is all
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3CorsaMeal
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Registered: 11th Apr 02
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i wonder if tyre wear accounts for anything, i don't know how much tread depth a tyre comes with, but your losing the few mm's twice on the overall diameter of wheel
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sand-eel
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Registered: 15th Mar 07
Location: carluke/braidwood--IRNBRULAND
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By law they have to over read!
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sand-eel
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Registered: 15th Mar 07
Location: carluke/braidwood--IRNBRULAND
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If you get bigger wheels from the factory spec, the speedo becomes more accurate, I remember in my corsa 205/40/17 tyres at 80mph the GPS was 80mph as well.
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Steve
Premium Member
Registered: 30th Mar 02
Location: Worcestershire Drives: Defender
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gps will be very accurate regardless of how much it cost the equation is still the same
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John
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Registered: 30th Jun 03
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quote:
Originally posted by sand-eel
By law they have to over read!
They can't under read by law, how could you have a law governing somebodys speedo being too accurate.
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3CorsaMeal
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Registered: 11th Apr 02
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so should a cars real mileage be 5% less than whats stated
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harrisp
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Registered: 15th Dec 07
Location: Derbyshire
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My car speedo seems bang on with gps, on tyres 3" bigger than standard.
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Rob R
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Registered: 31st May 03
Location: Kent
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When I'm doing 80 in my Civic I'm actually going 73, so mines near enough 10% out
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pow
Premium Member
Registered: 11th Sep 06
Location: Hazlemere, Buckinghamshire
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85 in the MiTo = 80 on the GPS, confirmed by tomtom, garmin and a range of andriod apps
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pow
Premium Member
Registered: 11th Sep 06
Location: Hazlemere, Buckinghamshire
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Oh and the prius is a consistant 10% out 
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Steve
Premium Member
Registered: 30th Mar 02
Location: Worcestershire Drives: Defender
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you'l often find there is ecu mph and what you see on the clocks, not sure how it works but usually the mph the ecu registers is more accurate then what you see on the dials
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Fro
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Registered: 20th Jun 06
Location: Rainham, Essex Drives: A3 2.0TDi Sport
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quote:
Originally posted by Steve
you'l often find there is ecu mph and what you see on the clocks, not sure how it works but usually the mph the ecu registers is more accurate then what you see on the dials
Correct from experience.
My 350z has digi speed and clocks, digi is always higher.
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John
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Registered: 30th Jun 03
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Clocks are deliberately out, quite a few of them you can adjust the accuracy, the mileage is probably more accurate than the mph in the same set of clocks.
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whitter45
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Registered: 15th Nov 02
Location: Norton
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95 in the BMW is 89 on GPS
Worst cars for over reading used to be fords in particular the focus
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DaveyLC
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Registered: 8th Oct 08
Location: Berkshire
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quote:
Originally posted by Steve
you'l often find there is ecu mph and what you see on the clocks, not sure how it works but usually the mph the ecu registers is more accurate then what you see on the dials
They come from the same signal so why would they be different you dingus.
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Steve
Premium Member
Registered: 30th Mar 02
Location: Worcestershire Drives: Defender
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probably because the dials needles are positioned slightly ahead of what the signal provides  at a guess
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John
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Registered: 30th Jun 03
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It's because the dials are programmed to be slightly innacurate, nothing to do with the accuracy of the speed signal.
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Nath
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Registered: 3rd Apr 02
Location: MK
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quote:
Originally posted by Steve
gps will be very accurate regardless of how much it cost the equation is still the same
GPS is only as accurate as the measurement engine in the reciever.
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Steve
Premium Member
Registered: 30th Mar 02
Location: Worcestershire Drives: Defender
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dont even think that matters, it could take 3 readings and regardless of the pin point of the readings themselves, the equation to work out the speed qould still be very accurate, far more then a speedo anyway
or im talking shit, one or the other
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Nath
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Registered: 3rd Apr 02
Location: MK
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quote:
Originally posted by Steve
dont even think that matters, it could take 3 readings and regardless of the pin point of the readings themselves, the equation to work out the speed qould still be very accurate, far more then a speedo anyway
or im talking shit, one or the other
It does. Hence why Car GPS isn't as accurate as Surveying GPS. Car GPS is accurate to a few metres, positional wise, but Surveying GPS is accurate to milimetres, Due to the way its calculated from the satelite signals. It's accurate enough in a car/phone, but not the most accurate. Which is why some car GPS doesnt show your on a sliproad for example, it doesnt exactly know where you are.
[Edited on 09-09-2010 by Nath]
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Steve
Premium Member
Registered: 30th Mar 02
Location: Worcestershire Drives: Defender
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yeah but if you think about it, it doesnt matter if its only accurate to a few meters as long as the other readings are equally as innaccurate it wouldnt matter
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Nath
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Registered: 3rd Apr 02
Location: MK
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quote:
Originally posted by Steve
yeah but if you think about it, it doesnt matter if its only accurate to a few meters as long as the other readings are equally as innaccurate it wouldnt matter
I dunno, I just know it's not all that accurate. I work with Surveying equipment and had to hear all about how accurate it is in a presentation. Boring 
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Fro
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Registered: 20th Jun 06
Location: Rainham, Essex Drives: A3 2.0TDi Sport
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quote:
Originally posted by Nath
quote:
Originally posted by Steve
dont even think that matters, it could take 3 readings and regardless of the pin point of the readings themselves, the equation to work out the speed qould still be very accurate, far more then a speedo anyway
or im talking shit, one or the other
It does. Hence why Car GPS isn't as accurate as Surveying GPS. Car GPS is accurate to a few metres, positional wise, but Surveying GPS is accurate to milimetres, Due to the way its calculated from the satelite signals. It's accurate enough in a car/phone, but not the most accurate. Which is why some car GPS doesnt show your on a sliproad for example, it doesnt exactly know where you are.
[Edited on 09-09-2010 by Nath]
Majority dont count gradients either iirc?
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DaveyLC
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Registered: 8th Oct 08
Location: Berkshire
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quote:
Originally posted by Steve
probably because the dials needles are positioned slightly ahead of what the signal provides at a guess
Nothing to do with converting a Digital signal to an Analogue one then? 
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