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    @hibs.net private member Peevemor's Avatar
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    Daft car question

    Like most cars, my speedo indicates that I'm going faster than I actually am (compared with the GPS). However mine exaggerates more than most, with the speed shown being more than 8% higher than the reality (eg. 110km/h on GPS = 119 on the speedo).

    Will the total distance clocked by my car also be 8%+ higher than the reality?

    It's not at all important, I'm just wondering.


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  3. #2
    @hibs.net private member Scouse Hibby's Avatar
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    Quote Originally Posted by Peevemor View Post
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    Like most cars, my speedo indicates that I'm going faster than I actually am (compared with the GPS). However mine exaggerates more than most, with the speed shown being more than 8% higher than the reality (eg. 110km/h on GPS = 119 on the speedo).

    Will the total distance clocked by my car also be 8%+ higher than the reality?

    It's not at all important, I'm just wondering.
    GPS Speed vs. Vehicle Speedometer. With a clear view of the sky, GPS speed has shown to be more accurate than most vehicle speedometers. ... Your vehicle speedometer accuracy can vary based on several factors, most notably differences in wheel size due to wear, pressure.

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    @hibs.net private member Peevemor's Avatar
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    Quote Originally Posted by Scouse Hibby View Post
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    GPS Speed vs. Vehicle Speedometer. With a clear view of the sky, GPS speed has shown to be more accurate than most vehicle speedometers. ... Your vehicle speedometer accuracy can vary based on several factors, most notably differences in wheel size due to wear, pressure.
    I understand that, but is the total distance clocked by the car linked to the speedo? My car shows that it's done about 210k km, but could that be 8% or whatever less in reality?

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    Quote Originally Posted by Peevemor View Post
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    I understand that, but is the total distance clocked by the car linked to the speedo? My car shows that it's done about 210k km, but could that be 8% or whatever less in reality?
    I think the odometer normally works by counting wheel rotations.

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    @hibs.net private member Peevemor's Avatar
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    Quote Originally Posted by RyeSloan View Post
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    I think the odometer normally works by counting wheel rotations.
    As does the speedo, but do the 2 things take their information from the same place (which would seem logical)?

    For example, if I drive at 119km/h (on the speedo) for one hour, will the odometer clock 119km, even though in reality I'll have only done 110km?

    If this is the case, my odometer is well wrong. It's currently at about 210k km, when in reality the car's done less than 195k.

    It's no big deal as I plan to run the car until it's dead (or almost), it's just one of these daft things that's got me thinking.

  7. #6
    @hibs.net private member Scouse Hibby's Avatar
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    Quote Originally Posted by Peevemor View Post
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    I understand that, but is the total distance clocked by the car linked to the speedo? My car shows that it's done about 210k km, but could that be 8% or whatever less in reality?
    GPS tracking devices have traditionally only given reasonably accurate mileage data ó they typically don't tell you what your odometer readings is. ... The system uses information from the engine to calculate odometer, and is generally slightly over actual miles traveled.
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  8. #7
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    That is a very good question. I really don't know.

    I have always noticed that the speedo is way over reading. Say by 10% at 30mph but way more at high speeds.

    I was stopped by the police when my speed indicated 104 mph but the police camera said 88 mph. No excuses for that speeding like that I know. In my youth.

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    Quote Originally Posted by Peevemor View Post
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    As does the speedo, but do the 2 things take their information from the same place (which would seem logical)?

    For example, if I drive at 119km/h (on the speedo) for one hour, will the odometer clock 119km, even though in reality I'll have only done 110km?

    If this is the case, my odometer is well wrong. It's currently at about 210k km, when in reality the car's done less than 195k.

    It's no big deal as I plan to run the car until it's dead (or almost), it's just one of these daft things that's got me thinking.
    I suppose the speedo is also factoring time so therefore has a greater margin of error. Also is your speedo a manual gauge / needle? If so then you have the error of the display of the speed as well as the calculation to account for.

    But distance is simply counting wheel rotations (no matter how fast the wheel is rotating) so should be much more reliable as the circumference of the wheel is known (or at least to a high degree of certainty...as long as your tyres are inflated properly etc). Itís then a simple matter of rotations x circumference = distance

    So with no expert knowledge whatsoever I would proffer my position that that the accuracy of your speedo is no indicator of the accuracy of your odometer

  10. #9
    @hibs.net private member Peevemor's Avatar
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    It's a needle, so it could well be set up incorrectly - I hadn't thought of that.

    Doesn't mean I'll sleep tonight.

  11. #10
    Private Members Prediction League Winner Hibrandenburg's Avatar
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    Speed = distance ų time.

    Time (generally) isn't variable therefore logically the false reading in speed can only be accounted for due to inaccuracies in the measuring of distance. It therefore stands to reason that your mileage reading will also be inaccurate.

  12. #11
    Itís illegal to make a car with a speedo that says youíre going slower than you are. They have to allow for a certain amount of inaccuracy, so the result is that theyíre all calibrated on the safe side and show you going faster than you are.

    Odometers donít have that issue and are much more accurate.

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    @hibs.net private member Peevemor's Avatar
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    Quote Originally Posted by Hibrandenburg View Post
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    Speed = distance ų time.

    Time (generally) isn't variable therefore logically the false reading in speed can only be accounted for due to inaccuracies in the measuring of distance. It therefore stands to reason that your mileage reading will also be inaccurate.
    Quote Originally Posted by JeMeSouviens View Post
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    Itís illegal to make a car with a speedo that says youíre going slower than you are. They have to allow for a certain amount of inaccuracy, so the result is that theyíre all calibrated on the safe side and show you going faster than you are.

    Odometers donít have that issue and are much more accurate.
    Fight! Fight! Fight! Fight!...

  14. #13
    Quote Originally Posted by Peevemor View Post
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    Fight! Fight! Fight! Fight!...
    Itís not that the speedo couldnít be as accurate, itís deliberately calibrated not to be.

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    Private Members Prediction League Winner Hibrandenburg's Avatar
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    Quote Originally Posted by Peevemor View Post
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    Fight! Fight! Fight! Fight!...
    Both answers aren't mutually exclusive.

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    @hibs.net private member Peevemor's Avatar
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    Quote Originally Posted by JeMeSouviens View Post
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    Itís not that the speedo couldnít be as accurate, itís deliberately calibrated not to be.
    Makes perfect sense.

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    @hibs.net private member Peevemor's Avatar
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    Quote Originally Posted by Hibrandenburg View Post
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    Both answers aren't mutually exclusive.
    ;-)

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    Testimonial Due Hibby70's Avatar
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    Hence why Dr Emmett Brown used his own digital speedometer in the DeLorean.

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    Coaching Staff One Day Soon's Avatar
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    Best .net thread ever.

  20. #19
    @hibs.net private member Hibs Class's Avatar
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    Quote Originally Posted by JeMeSouviens View Post
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    Itís not that the speedo couldnít be as accurate, itís deliberately calibrated not to be.

    It's based on an EU standard - details here https://www.thecarexpert.co.uk/how-a...r-speedometer/

    I think I'm right in saying there isn't an equivalent standard in e.g. USA, so their speedos are more accurate.
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    @hibs.net private member Andy Bee's Avatar
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    I drive one of four different trucks to the Lancaster area every night, to the exact same place in the exact same type and year of truck. Mileage ranges from 482 to 503km depending on which truck I drive but the 482km truck is the fastest even though they're all limited to 56mph, go figure

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    @hibs.net private member Peevemor's Avatar
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    Quote Originally Posted by Andy Bee View Post
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    I drive one of four different trucks to the Lancaster area every night, to the exact same place in the exact same type and year of truck. Mileage ranges from 482 to 503km depending on which truck I drive but the 482km truck is the fastest even though they're all limited to 56mph, go figure
    Excellent! Long live the thread!

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    Testimonial Due Hibby70's Avatar
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    So are we saying that if you fit monster wheels to your Ford fiesta that are twice the circumference of the standard ones you'll actually do twice the distance to that shown on your odometer?

  24. #23
    @hibs.net private member Peevemor's Avatar
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    Quote Originally Posted by Hibby70 View Post
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    So are we saying that if you fit monster wheels to your Ford fiesta that are twice the circumference of the standard ones you'll actually do twice the distance to that shown on your odometer?
    Yup. And twice the speed indicated on the speedo.

  25. #24
    @hibs.net private member danhibees1875's Avatar
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    I'm imagining Vauxhall Corsa's being modified to look like penny farthings once the information above goes mainstream.
    Mon the Hibs.

  26. #25
    @hibs.net private member Hibbyradge's Avatar
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    Quote Originally Posted by danhibees1875 View Post
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    I'm imagining Vauxhall Corsa's being modified to look like penny farthings once the information above goes mainstream.
    That would be quite fitting as it's exactly what they're worth.
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  27. #26
    @hibs.net private member McSwanky's Avatar
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    Quote Originally Posted by Andy Bee View Post
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    I drive one of four different trucks to the Lancaster area every night, to the exact same place in the exact same type and year of truck. Mileage ranges from 482 to 503km depending on which truck I drive but the 482km truck is the fastest even though they're all limited to 56mph, go figure
    Off topic, but can I just say, your profile pic is without a doubt the best one I've ever seen. Might just nick that for other places!!!

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    @hibs.net private member Jack's Avatar
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    I'm on a fag run this weekend and one of the guys is a car mechanic. He's very good but I've never recommended him on here cause he's a jambo!!!

    He's never considered this question but made a few points.

    Firstly the measuring stuff is all calibrated for when it leaves the factory, no surprise, so it's all downhill from then re accuracy. Wear on the tyres being the obvious one.

    It depends what car, or vehicle, your talking about as various makes take take the information from different places, the gearbox among others and surprisingly,for me anyway, BMW and Mercedes from the ABS system. It takes a reading from the 4 wheels and works out the average of the 4 for speed and distance!

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