Member Since: 01 Aug 2008
Location: Roodeplaat
Posts: 84
Speed indicators
Hi Guys, some advice needed, please, but it requires a bit of explaining, so please bear with me. The question is about the software settings that are seemingly for calibrating the speed indicators in the D4. I have a South African Disco4 SDV6 HSE, 2014 model, and am using an IIDTool BT with latest firmware and iPhone 4S interface. On the IIDTool's IPC-Instrument pack module it gives the option to adjust what is called "Speed scaling factor" and "KPH off-set".
Let me first state what the situation was before any adjustments: KPH off-set at +2kph and Speed scaling factor set at +3.5%. Running at a steady true speed (hand-held GPS) of 129kph with the car on cruise control on a level road (no change in speed), the analog speedometer dial, the digital speed indicator at the bottom right on the message centre, as well as the “Cruise Setspeed†indicator at the top of the message centre all show 135kph.
I then changed the KPH off-set to 0kph and the Speed scaling factor to 0%. Again running at true speed of 129kph with cruise control engaged, the analog speedometer dial and the digital speed indicator still show 135kph, but the Cruise setspeed indicator now shows 128kph. Here is a picture to show this.
My logic tells me that the adjustments I made did change at least some measurements/outputs of the car (otherwise the Cruise setspeed would not have changed from 135 to 128kph) but that the adjustments do not register everywhere it should, specifically not the analog and digital speed dials’ input.
Any similar experiences and advice to offer?
Thanks very much!
Danie
16th Apr 2015 3:17 pm
Robbie
Member Since: 05 Feb 2006
Location: ¯\_(ツ)_/¯
Posts: 17932
I've not tried this but I know the speedo CCF settings are in a number of places and not all are used. My 'as built' are as below and I am happy to tweak them in the same way, but it would be best to change just one parameter at a time so we can establish exactly what it does.
Member Since: 01 Aug 2008
Location: Roodeplaat
Posts: 84
Thanks for your response, Robbie. I will reset the two values to what it was previously and then start one at a time.
By the way, I noted today that the "Live Values" in the "PCM-Engine SDV6" menu shows the Vehicle Speed to be the lower, more accurate value (related to 128kph in my first post), and not the same value as the two speedometers... Same goes for Wheel Speed. Thus, the adjustments definitely adjusted a number of the behind-the-scenes values, but (frustratingly) not the speedometers.
Will keep playing...
Regards,
Danie
17th Apr 2015 9:50 am
mse
Member Since: 27 Jun 2005
Location: Shropshire
Posts: 2702
Just one point - don't trust your GPS to provide accurate speed reading...they don't and can range between close to just as off as the thing you are trying to correct.
The higher speed the more potential for an error. Before trusting a hand-held unit, I would want a calibrated unit.
On the detail of changing the speed reading - why would you want to, is only a few KPH out and its always in your favour.Mike
21st Apr 2015 11:05 am
Robbie
Member Since: 05 Feb 2006
Location: ¯\_(ツ)_/¯
Posts: 17932
You would be pretty unlucky to have 0.5 mph error in a GPS. With a good signal and geometry they usually achieve better.
Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 27 Jun 2005
Location: Shropshire
Posts: 2702
GPS accuracy of speed and position can vary widely - ive seen it be some be mph out off speed 1 or 2 - when at 100's + it doesn't really matter. As you know there are so many factors that can cause speed inaccuracy against position inaccuracy - especially within vehicle situations.
Yes a WAAS enabled GPS, good line of site (eg probably out of the car) and a good GPS unit should be around 0.5mph out, possibly between 0.25 and 0.75(which links to how it calculates, eg does it average over a period or do different calculations? Many garmin handhelds take a point every second so could be 30m out at 120kph or so {im not doing maths this morning!!}).
So assuming 1mph error on a good day, with a good unit in the car that's 1.6kph out already - can easily see that being increased without to much hardship
The OP was only talk 6kph so I could see a GPS error of around 3kph as easily possible from say a walkers (or phone) GPS inside a car.
Hence, don't rely on it to get the car speedo perfectly accurate
There are of course many other errors and issues potentially likely - hence RNAV work in flying etcMike
21st Apr 2015 12:17 pm
daniem
Member Since: 01 Aug 2008
Location: Roodeplaat
Posts: 84
The reason for doing this is just because I like it when things are correct (personal taste), and thus I want the speedo to indicate as closely as possible to true speed. I am testing on a flat, straight road, where I run at the 135kph (or whatever) indicated speed for a couple of km, continuously checking the car vs the GPS reading, and thus not just a spot check while the car is accelerating or decelerating. Hopefully this gives me a fairly accurate state of affairs.
I have not been able to play around as much as I had hoped, but did change both settings back to the original (KPH off-set at +2kph and Speed scaling factor set at +3.5%), checked that it again shows what I found originally, and then changed only the Speed scaling factor to +0.5%. Why not 0.0% you ask? I read (generic, not IIDTool specific) that sometimes changing a value zero causes the software not to register the change. The result is that it now indicates the following with the GPS on 129 (as per my original test):
Analog Speedo: 135kph (no change when I changed the setting)
Digital speedo: 135kph (no change when I changed the setting)
Cruise setspeed: 131 kph (CHANGED)
Wheel speed on Live values of IIDTool: 128 kph (no change when I changed the setting)
Car speed on Live values of IIDTool: 128 kph (no change when I changed the setting)
Strange things here:
1) The Live Values seems to indicate very close to the GPS, regardless of the state of the two settings (and does not adjust as I had thought in a previous post).
2) The speedos indicate a positive offset of around 5% to the Live values, regardless of the state of the two settings.
3) The only thing I can find that does change with the changed settings is the Cruise set-speed, which does not help my quest at all.
I will test further this weekend, but at this stage it seems that I should rather leave it on the original setting where at least the speedos and the cruise set-speed agree, and then not worry about it further.
Regards,
Danie
24th Apr 2015 9:34 am
RSAChris
Member Since: 16 Apr 2010
Location: Centurion RSA
Posts: 154
Hi Danie
I can report the same results as you.
I also got to play last night and also set the values to 0 as you did initially. Just one small difference: my GPS shows the same as the Vehicle speed (128), when both speedos are on 135km/h.
I will also play with the setti gs and give feedback here.
Cheers
CSProud owner of an IIDTool
2010 Disco 4 TDV6 SE
R2D3 the 2007 Disco 3 TDV6 SE... gone now
Romulus [Defender 110 CSW Td5] will always be missed
Rofty [Defender 110 CSW Td5] first Td5 and start of motor electronics...
www.flickr.com/photos/the_steyns
20th May 2015 12:56 pm
RSAChris
Member Since: 16 Apr 2010
Location: Centurion RSA
Posts: 154
OK, had a lazy weekend and played with the speed settings.
None of the changes could affect the speedometer and digital speed reading. Only changes to the IID tool Vehicle speed and the Cruise control altered. I opted for 0 on both settings, as the Cruise speed now indicates the GPS speed.
O and some more: The Autolamp delay for reverse lights does not work on my 2010 model... sadly...
Cheers
CSProud owner of an IIDTool
2010 Disco 4 TDV6 SE
R2D3 the 2007 Disco 3 TDV6 SE... gone now
Romulus [Defender 110 CSW Td5] will always be missed
Rofty [Defender 110 CSW Td5] first Td5 and start of motor electronics...
www.flickr.com/photos/the_steyns
25th May 2015 8:27 am
Robbie
Member Since: 05 Feb 2006
Location: ¯\_(ツ)_/¯
Posts: 17932
The other option would be to change the tyre rolling circumference setting.Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 16 Apr 2010
Location: Centurion RSA
Posts: 154
... homework... Proud owner of an IIDTool
2010 Disco 4 TDV6 SE
R2D3 the 2007 Disco 3 TDV6 SE... gone now
Romulus [Defender 110 CSW Td5] will always be missed
Rofty [Defender 110 CSW Td5] first Td5 and start of motor electronics...
www.flickr.com/photos/the_steyns
Thanks for this thread guys, I now know where to look to correct the annoying 1mph/2kph discrepancy between speedo and SetCruise control speed which has appeared about a year ago and not due to my tinkering as I only just got an iid LRs are a fond memory, apart from the maintenance.
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