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Thread: Speedo vs Road Speed

  1. #1
    Senior Member AdelaideSRT's Avatar
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    Speedo vs Road Speed

    OK, so through a roundabout method, I discovered that the speed shown on my old satnav was actually more accurate than the dash, in the Statesman - and had double checked it with those road side speed signs on the Hume Highway whilst running around in a rented XR-6 - if we assume it's still pretty much spot on for what it should be, I'm looking at a rough 10% slower speed than the dash is telling me in the VT. That's actually good news, if I'm 'creeping' at 65 kmh, I'm actually doing 60 so should be fairly safe from the boys in blue - likewise my 'usual' 110 on the open road is 100, and again, that's usually the 'turn a blind eye' zone for most SA coppers...

    All good, I have some leeway on the speedo... thing is though, this, to me, explains some of the inaccuracies with the distance to empty, the estimated fuel economy, etc - if I drive for an hour at 100 kmh on the dash, I've probably travelled 90 kilometres... but the car THINKS it's 100. Whatever it's calculating at that point is going to be thrown out all round. (This could help explain some of those people I find at various speeds under the limit when I'm actually thinking about what speed *I'm* doing... "Come on... it's an open road, you can do MORE than 80 now, honest" is a frequent comment on the run down to Victor on the back roads lol)
    Manual Veloster SR Turbo in Marmalade

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  3. #2
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    Old news SRT .. all car speedos are out and will always show speeds higher than actual (protects car manufacturers from law suits).

    I don't think you are correct on the distance travelled. If the odometer shows 100ks them that is the true distance travelled.

  4. #3
    Senior Member AdelaideSRT's Avatar
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    So we're working on the theory that the odometer 'measures' separately to the speedometer, or that the speedometer is displaying a different (lower) speed? I guess I'm more used to being 5% out rather than 10% out - hey, on the rotaries I was in mph anyway, so had to mentally convert - who am I kidding, when I had those I didn't care about speed limits, just who I was in front of... lol
    Manual Veloster SR Turbo in Marmalade

  5. #4
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    For what it is worth, not long after taking delivery of my Silver DCT Plus I noticed that my speedo seemed to register well over my actual speed (100kph true + 108 on speedo) Not sure if it effects the odometer? and thus the L/100km which in my case has been just under 7 around town.
    Anyway I contacted Customer Care by email, and below is the response.

    Thank you for contacting Hyundai Customer Care.

    We would recommend that your local Hyundai Dealer’s Service Department escalate the Audio reception matter to our Head Office Technical Support division for a diagnosis.

    Below in black, our technical Department have also supplied us with the ADR requirement that the Hyundai and all other manufactures work by: They have also advised that some portable GPS’s (Window mount) have been found to supply lag time data results pending satellite locations, but we have no way of testing this or your unit which they do not recommend or use in any form of speedo testing.
    Australian Design Rules (ADR) SPEEDO
    When vehicle manufacturers install a speedo at the factory, the speedo has been calibrated using data that assumes the vehicle is fitted with new standard tyres inflated to full pressure, on standard rims, and usually the tyre circumference has been measured before the wheel is put on a vehicle or when the vehicle is on a hoist (no load on tyre). When they test the car for compliance with the ADR, the speedo will invariably produce an over-read result.
    The current Australian Design Rules require speedos to be calibrated when the vehicle is unladen, fitted with normal tyres inflated to full pressure with an allowance for tyre heating:
    "Unladen vehicle" means the vehicle in running order, complete with fuel, coolant, lubricant, tools and a spare wheel (if provided as standard equipment by the vehicle manufacturer), carrying a driver weighing 75 kg, but no driver's mate, optional accessories or load.
    "Tyres normally fitted" means the type or types of tyre provided by the manufacturer on the vehicle type in question; snow tyres shall not be regarded as tyres normally fitted;
    "Normal running pressure" means the cold inflation pressure specified by the vehicle manufacturer increased by 0.2 bar.

    The current ADR prohibits any under-reading:
    "5.3. The speed indicated shall not be less than the true speed of the vehicle. At the test speeds specified in paragraph 5.2.5. above, there shall be the following relationship between the speed displayed (V1 ) and the true speed (V2).
    0 ≤ (V1 - V2) ≤ 0.1 V2 + 4 km/h."
    This formula means that the vehicle's actual (true) speed must not be greater than the displayed speed. (Displayed speed minus true speed must be greater than or equal to 0, and less than or equal to 4kmh plus 10% of true speed). This means that if your vehicle's actual speed is 100kmh, the displayed speed is permitted to be anywhere between 100kmh and 114kmh.
    Once again, Thank you for contacting Hyundai Customer Care.

  6. #5
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    As you have suggested, the speed readings have been sorted and you can expect the 10% error or close to it over reporting of the speed.

    From my experience with other Hyundais, this is the norm. However from my investigations in other Hyundais I have found that the odometer reading is not out by this amount.

    My most thorough investigations were in an i30. I used a Scangauge connected to the ODB2 port and found that this device reports distance and speed that is no more than 1% from real world distances and speed, out of the box, without recalibration. Only minimal correction was required. With a GPS I was able to recalibrate the Scangauge to be accurate using a 1% correction. Over a full tank of fuel, the distance travelled error calculated by comparing the ODB2 data read by the Scanguage (after recalibration) against the odometer reading was no more than 7km in 1200km, thats an error of 0.58%.

    Now I realise that was with an i30, but it does illustrate that it can not be assumed that errors in distances reported by the odometer are directly related to the errors with the speedo or vice versa.

  7. #6
    Senior Member AdelaideSRT's Avatar
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    Same gps, my wife's new X3, she's on the 5% over road speed that I expected - and sure enough, both of us side by side doing "60", and she drifts ahead of me - out of them all, I trust the gps because it matches what Vic main roads say the vehicle speed is, too... Nice to see Hyundai think it shouldn't be trusted for measurement

    Having just washed the X3, I love my Veloster even more... Boy that's a lot of car to wash and dry lol


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    Manual Veloster SR Turbo in Marmalade

  8. #7
    Junior Member TheBlackBass's Avatar
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    From using the TORQUE app and OBD2 reader. The ECU knows how fast you are actually going yet the speedometer will show something different. Mine, for example, is off 5%. It reads 84mph on the dash while the ECU states I am going 80. The ECU reading and GPS speeds match. Everything I can tell runs off the ECU speed, the mileage, MPG, etc, except for the actual dial.

    This is on my VT btw.

  9. #8
    Senior Member Evan L's Avatar
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    anyone ever see the MCM episode on correcting the speedo? so if everything but the speedo is run from the ecu, does that mean we could do their mod on the dial and have a more accurate reading?

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    Quote Originally Posted by Evan L View Post
    anyone ever see the MCM episode on correcting the speedo? so if everything but the speedo is run from the ecu, does that mean we could do their mod on the dial and have a more accurate reading?
    I haven't seen the episode, but I suspect the speedo is using the same sensor either directly or via the ECU (OBD2). It is just that like most manufacturers, Hyundai speedometers readjust (calibrate) the information received by the dash unit to fit the regulations for speedometers that Hyundai quoted to magnagusta above

    The speedo errors being experienced by Veloster owners are within a range of 0-2kph that I have experienced in 5 other Hyundais over the last 6 years. I've learned to live with it knowing that I am driving within the speed limits. When I creep over a little, I know that I am safe from attracting the wrath of the law.

  11. #10
    Senior Member blackjack's Avatar
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    Quote Originally Posted by SRobz View Post
    Old news SRT .. all car speedos are out and will always show speeds higher than actual (protects car manufacturers from law suits).

    I don't think you are correct on the distance travelled. If the odometer shows 100ks them that is the true distance travelled.
    Actually not 100% correct SRobz, my 2009 i30 is actually 100% spot on at all speeds, have checked via GPS and those speed detections devices on our highways. All show the exact same reading. Reckon it must be a fault in the car...
    But its good to actually drive a car that is correct, takes the guess work out of driving.

  12. #11
    Senior Member cbrmale's Avatar
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    I stuck my old GPS on the windscreen of the Veloster and noted the speedo error at 60, 80, 100, 110 and 120 (the speed that's allowed in NSW before you get booked). It was 5 out at 60 and 6 out at 100 - 120. So that's what I drive to (freeway cruise speed is half-way between 120 and 130 = 119). I bought a GPS for my motorcycle and the speedo on that is even worse! It's 7 out at 100 through 120. It's such an odd number that I ride the motorcycle to the tacho: 4,400rpm in 5th is a whisker under 120 while 3,900 is right on 100 actual, and so on.

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