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~Rich~
Member Since: 16 Mar 2009
Location: Sydney
Posts: 628
  
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Yeah I noticed this too with many different brands of vehicles, all read higher than actual.
I always use my GPS to set the cruise control, depending on which state you are driving on how much over you can get away with. 
I am running oversize Cooper LTZ's and the speedo is just about spot on now!
Photos in Gallery.
755mm standard - 799mm Coopers. 2014 SDV6 HSE White, LLAMS Height Controller, Tinted Glass, Tuff Ant Sliders and 18" steel wheels, Safari Snorkel, Rhino Rack Platform, ARB Air Compressor, Custom Drawer and storage unit -http://www.box.com/s/jem0ilac3cner2mexq64 UHF CB, 4x4 Intellegence RWC, 120ltr Long range tank, Rock Sliders and Compressor protection plate Beanie grill, De Tango.
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 26th Feb 2010 3:20 am |
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DingMark
Member Since: 14 Sep 2007
Location: Perth Oz or Erbil, Iraq
Posts: 388
 
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On a new-ish highway near here I always take a new vehicle and test the speed at 100km over odometer calibration signs exactly 5km apart. Using different GPS's, they have all been very close to accurate, while most vehicles are 5%-10% slow. This is consistent with what this thread has said, but I'll trust the fixed odometer calibration signs more than anything else. It seems there's a consensus that the D3s and D4s read more or less 5-7% low. Jim Dowell - D4 HSE TDi, 12,000 hydraulic winch & hidden winch mount, MTRs, TyreDog, Traxide 2 x aux battery system, fixed air compressor, Dolium roof rack, MitchHitch.
RIP 2005 D3 HSE V8 5 seater gold (stolen and torched)
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| 26th Feb 2010 5:55 am |
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SGK
Member Since: 09 Jun 2006
Location: Melbourne
Posts: 40
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No luck so far. Landrover service says that they have no idea on recalibrating and that to the best of their knowledge it can bot be done.
The annoying thing is that the Speedometer actually seems to be very consistent accross the range - so just setting it properly would be enough. HELLLOOO LANDROVER: A software update could make this possible may be???
sgk Prado Grande --> D3 --> D4 ... its getting better all the time
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| 26th Feb 2010 8:08 am |
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DG
Site Moderator
Member Since: 12 Dec 2005
Location: The Gaff
Posts: 50978
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Why would they want to  No other manufacturer does. 21 year LR veteran > D2 GS 2003 > D3 S 2006 > D3 HSE 2009 > D4 HSE 2013 > D4 HSE 2015 > D5 HSE 2018 > DS HSE R-Dynamic P300e 2021
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| 26th Feb 2010 8:17 am |
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GraemeS
Member Since: 17 Mar 2008
Location: NSW
Posts: 706
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I have been told that the D3 sat-nav system has a calibrate function that's thought to use its GPS speed to correct speedo inaccuracies. The owner of the D3 had used the function but at the time did not know if it actualy changed anything.
Has anyone else encountered this facility and know just what is achieved, if anything?
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| 26th Feb 2010 8:27 am |
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DG
Site Moderator
Member Since: 12 Dec 2005
Location: The Gaff
Posts: 50978
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The reason they won't bother is that they cannot afford to have the speedo readout dropping below the true speed.
Varying factors will affect the true speed compared to readout on the dial ...that is why for example in the UK a police traffic vehicle has to have its speed equipment certified as calibrated every time the vehicle goes out...because it will change over short period of time. In the olden days they used to have a seperate calibrated unit in the centre of the dash for checking speeders and would ignore the OEM unit.
I don't think you will get what you are asking for from LR ...or any other manufacturer TBH..but there are plenty 'racetech' type companies that will supply you with an aftermarket unit I'm sure 21 year LR veteran > D2 GS 2003 > D3 S 2006 > D3 HSE 2009 > D4 HSE 2013 > D4 HSE 2015 > D5 HSE 2018 > DS HSE R-Dynamic P300e 2021
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| 26th Feb 2010 8:41 am |
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Alicatt
Member Since: 10 Jul 2007
Location: Eating in Eksel or Working in Wick
Posts: 320
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Not for the LR D3/4 etc.
In my MG ZT with the BMW electronics, if you enter the service menu on the instrument cluster then you get an offset for correcting the speedo and the procedure is documented in the service manual for the car (RAVE2)
There is also a separate "offset" for the satnav to correct for the slight diffrences in the speed sensors on the wheels (for the ABS)
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| 26th Feb 2010 9:50 am |
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TSR2
Member Since: 22 Jul 2008
Location: North Lincolnshire
Posts: 1104
  
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Sounds interesting Alicatt. Did it say how accurate the system was and did they guarantee the accuracy?? What if you messed up the recalibration did it always leave you on the safe side?? Regards, Trev.
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In the wilds of North Lincs or the middle of the North Sea.
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| 26th Feb 2010 10:12 am |
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hensoni
Member Since: 01 Oct 2007
Location: Sleepy Somerset
Posts: 576
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In terms of GPS speed accuracy, GPS can be incredibly accurate at measuring velocities in all planes. However, car sat navs use a specific data interface called NMEA 0183. The interface is split into data sentences (strings of data words) with each data word containing the native GPS info.
The use of NMEA interface leads to several features - one, the "M" stands for "marine" so most users of the standard only transmit the horizontal component of the GPS velocity signals (Vx) as ships don't go uphill. If you drive up and down hills, then the velocity will be inaccurate due to the missing vertical component (Vz).
Secondly, the NMEA interface only updates once per second. Thus, your "raw" data from the GPS receiver is being strangled by the data interface. Cars and all other vessels / vehicles are constantly changing their velocities - GPS can track those changes, so can the speed sensor on the gearbox. The NMEA interface cannot and nor can the driver. The speedo needle has to be damped to take out these constant changes otherwise the needle would moving all over the place. If a needle connected to a varying signal source is undamped, then it will always alternate between over and and under-reading. It will never read accurately! Smiths made instruments like this for many years.
So, by all means use the GPS data on the open road where gradients are less dramatic and the rate of change of speed is lower, but don't rely on it in stop / start traffic or when negotiating the bends and twists of a country road. Most importantly, never use GPS as a defence against a speeding offence - you'll lose.
Having said all of the above, it's a shame that the D4 speedo isn't accurate. My D3 speedo is refreshingly accurate - compared against 2 GPS receivers (with different chipsets and software) and monitored on a flat road at a (nearly) constant speed.
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| 26th Feb 2010 12:41 pm |
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