D4 Speedo v GPS

[LeaRoy]

Having tried to protable type GPS in my D4 I would like to know how accruate the speedo is in the D4.

According to both GPS the speedo is about 6km a hour faster.

I have the stardard 18" wheels and tyres on as supplied by the dealer.

Is this normal or is it something I should have checked by the dealer?

[mowog]

My D4 speedo is around 4k's slower than my Garmin GPS speed.

I think its case of living with it.

[101RRS]

The speedo is allowed to have a max error of 10% over - ie if the car is actually doing 100kph the speedo can read up to 110kph.

However the opposite is not allowed - the speedo cannot read less than actual speed.

The above applies to cars manufactured since about 2005/06. - ADRs.

So if you speedo is reading fast that is OK.

Garry

[Disco4SE]

Having tried to protable type GPS in my D4 I would like to know how accruate the speedo is in the D4.

According to both GPS the speedo is about 6km a hour faster.

I have the stardard 18" wheels and tyres on as supplied by the dealer.

Is this normal or is it something I should have checked by the dealer?
Hi Learoy, I have the D4 3.0 with 19" wheels and standard tyres. Mine is between 4 - 5 Kph faster than than the speed on my GPS.
I am told by ULR that they do this on purpose.
Cheers, Craig

[mowog]

My D4 speedo is around 4k's slower than my Garmin GPS speed.

I think its case of living with it.

Doh...

Make that faster.

Actual 96k via GPS, Displayed by speedo 100.

Maybe this is why the LR satnav has no speed display option.

[Jim621]

Im sure the manufactures also allow for tyre wear in the speedo design. id say its almost 2% allowance just for that.
Steve

[Graeme]

Im sure the manufactures also allow for tyre wear in the speedo design. id say its almost 2% allowance just for that.
Steve
That's going the wrong direction as the speedo will read faster again as the tyres wear.

I'm a cynic and think that LR does it to give the impression of better fuel economy.

[rmp]

The GPSR will be more accurate provided you maintain a constant speed for a few seconds in a straight line.

All car speedos over-read so you can't sue the manufacturer when you get a speeding ticket. This is by design.

With 19s, 18s etc you are referring to the rim diameter which is not related to the tyre diameter which is what is important for considering the effect on the speedo.

[powella]

The D3 computer actually has a tire Diameter figure. Assuming the D4 is the same, with the right tool, just change the tire diameter.

Cheers,
AP
P.S. mine is now dead on....

[PaulGOz]

I have the TDV6 D4 with 18 inch wheels and tyres from factory approx 8000kms and I am reading between 4 - 6kph indicated speed over the GPS speed. I often get 109kph on the GPS and 115kph on the dash. I just ignore the dash (or mentally adjust):) and go by the GPS just be careful when you enter a tunnel!

[xoa]

I have the D4 with 19" wheels. Just completed trip across the Simpson and routinely compared highway speeds of 100 km/h on GPS (Garmin 60 CSx) to 105 Km/h on Disco readout. 2 Landcrusiers on same trip read 101.

[RichardK]

The D3 computer actually has a tire Diameter figure. Assuming the D4 is the same, with the right tool, just change the tire diameter.

Cheers,
AP
P.S. mine is now dead on....

Yes, I have adjusted mine to be accurate with my GPS so there is no guesswork.

[Duck's Guts]

D4 with the new wheels & tyres (255/65x17) still result in a significant error. Pls note that this is the same diameter as factory 255/60x18's).

GPS vs Speedo km/hr is as follows:
40 - 43
50 - 54
60 - 65
70 - 75
80 - 85
90 - 95
100 - 105
110 - 116

[101RRS]

That is about what it should be.

Garry

[rmp]

D4 with the new wheels & tyres (255/65x17) still result in a significant error. Pls note that this is the same diameter as factory 255/60x18's).

GPS vs Speedo km/hr is as follows:
40 - 43
50 - 54
60 - 65
70 - 75
80 - 85
90 - 95
100 - 105
110 - 116

what it should be!

[Graeme]

I adjusted the D4's CCF speedo fudge factors to 0% and 0 kph but it made no difference. A 2nd look revealed the exisitance of a Calibration Market field which was set to Market 0: 3.5% & 2kph (which is what was originally in the the individual fields) so changed to the other option Market 1: 2% & 0 kph. However this caused the ABS ecu to produce a programming specification fault so I changed it back. The ABS ecu still objected until the ignition was recycled, even though all ecus were rebooted as part of the CCF rewrite. I'll try the market change again another day and cycle the ignition afterwards to see if the ABS ecu still objects. I'd rather not change the tyre size (except perhaps to my current slightly larger size) as my odometer was spot-on when checked against freeway 5km odometer check posts with the original 19" wheels.

[WhiteD3]

My 2.7 D4 on standard 255/60 R18 tyres reads ~8 KPH faster than the GPS at 100-110 KPH but just about spot on at < 80 KPH.

[outasight]

The speedo is allowed to have a max error of 10% over - ie if the car is actually doing 100kph the speedo can read up to 110kph.

However the opposite is not allowed - the speedo cannot read less than actual speed.

The above applies to cars manufactured since about 2005/06. - ADRs.

So if you speedo is reading fast that is OK.

Garry

Just in the interests of complete accuracy of information Garry, the relevant ADR allows for up to +10% + a flat 4 km/h on top of that!

So in fact doing a real 60km/h could be shown as high as 70km/h, or a real 100km/h could be shown as high as 114km/h !!!:wasntme:

Regards,

Les.

[Graeme]

I discovered today that cruise control setspeed uses the individual values in the speedo % and kph adjustment fields. I had left both fields at 0 (even though the market setting was for +3.5% & +2 kph) and CC setspeed now shows the precise speed if standard tyres were fitted. My tyres are 1.5-2% larger in diameter and the CC setspeed now shows 108 kph for a real 110 kph. Its a little strange cruising with the GPS showing 110, CC setspeed 108 and speedo 113-114. The slightly larger tyres have also made the odometer read about 2% less than it did with std tyres, no longer matching the 5 km calibration markers. The odometer and CC setspeed display could be corrected by specifying the fitted tyre size but that would return the speedo to 5-6 kph overstated instead of the current 3-4. I haven't finished fiddling yet.

[eddomak]

For those who are interested and have the aCar Android App, there is actually a gauge you can put on the digital dashboard which is specifically the value of the difference between the GPS speed and the engine management speed.

I too have noticed that the discrepancy is different at different speedo readings.

[Graeme]

My D4's speedo now shows proper speeds - yeh! It shows 100 when the GPS shows 99 with CC setspeed at 100 on a long, flat straight. The speedo market option of 2% + 0 kph has been selected. The tyres size is set to the fitted 245/70-17 so the odometer should be correct again but will be able to confirm on Monday. These tyres are reported to be 30.8" instead of the nominal 30.5" so the odometer may still understate marginally, as evidenced by the speedo not being a full 2% optomistic. The fuel economy factor has been set to -6% because changing from the original +7% to 0 still showed about a 6% discrepancy on a 500 km brim to brim check (10.1 display vs 10.67 actual).
Edit: the individual % & kph fields have been set to the same as the market option 2% + 0 kph - for CC use it seems.

[Graeme]

I'm still working away at getting the specs right. The odometer doesn't seem to honour the tyre size specs because its still reading 3% low. Perhaps it uses the rolling radius specification which has so far been unchanged but now increased by 10 mm to reflect the slightly larger tyres. Fuel consumption was pessimistic by 7% on 1 refill (495/510 kms) and 4% on a 2nd (450/463 kms), so the economy factor now set to -2%. No 950 km days again soon so it might be a while before any more worthwhile results.

[Wilbur]

Graeme, what device are you using to change these settings? I would very much like to get my speedo (and fuel economy) reading correctly.

Thanks,

Paul

[Graeme]

I'm using a Faultmate MSV2. The rolling radius had 1 for the most significant (left) byte and 116 for least significant (right) byte, making 372 (1 x 256 + 116) which is 9-10 mm less than the nominal radius of the standard tyre. It now has 1 & 126. Immediately the ABS ecu is reloaded it reports several faults presumably because its specifications have been changed, but none once the ignition is cyced. I then clear the faults and no more occur.

The speedo still shows 99-100 with 100 on the GPS after the increase in rolling radius, so the speedo parameters seem set. Its likely to be some time before I can check the odometer against freeway odometer check posts to confirm the rolling radius change is having the desired effect, but the odometer at least agrees with a 1000 m distance to destination check on the navigation device so I haven't particularly upset it.

[Wilbur]

Thanks Graeme,

Cheers,

Paul

[allisong]

I have also been trying out some settings in nmy RRS 2010 model. As standard it comes with 275/40/20 tyres but I have fitted the L322 rims (identical to my FFRR) with 255/50/20 tyres. Without any settings changes the speedo is now absolutely spot on at all speeds but the ODOmeter is around 4% low (for 100 miles on the GPS it reads 96 miles).

Also the vehicle is equipped with adapative crusie control and the fitting of larger tyres is claimed to affect this, although mine seems fine, very ocasionally I get "radar signal blocked" and then it disables the "forward alert function" until a recycle of the ignition. I don't think I get any more of these than before but I do know it uses the ABS singals along with the radar.

My tyre settings are MSB = 1 and LSB = 106 and the FFRR fitted with these tyres as standard is MSB = 1 and LSB =115.

Both have market settings of 3.5% + 2kph, but the RRS has individual settings of the same value and the FFRR has the individual settings as 0% and 0 kph.

Out of interest the trip computer fuel ecomomy setting is also +7%.

So I think I need to adjust the RRS to match the tyres and what you have discovered that the settings actually do is very interesting! What I have not found out is what the actual tyre circumference setting does and the tyre size setting as it seems to have no influence (in my case 2320mm).

If I find out some more I will post here.

[Graeme]

My D4 CCF does not appear to have a tyre circumference.

I have deduced that the tyre width, aspect and rim diameter are used to create the actual speed signal but that the speedo adjusts it according to the market specification of +3.5% & +2kph or +0% & +2kph as the only options. The suspension ecu seems to use the actual speed generated by ABS that's broadcast on the HS canbus, not the market specification adjusted speed shown by instruments.

I have deduced that cruise control uses the speed signal generated from tyre size and the individual values matching +3.5% & +2kph or whatever is selected, noting that 0% & 0kph are available. Setting these values different to the speedo values results in CC speed different to the speedo. (It looks odd to set CC and see setspeed quite different to the speedo whilst travelling at a constant speed.)

I have deduced that the dynamic rolling radius Most Significant Byte and Least Significant Byte are used for the odometer. The decimal values are converted to hex then the pair of hex bytes formed by the MSB and LSB in hex (now a word) are converted to decimal to produce the dynamic rolling radius in mm. Hence 1 & 106 results in 362mm dynamic rolling radius and 1 & 115 results in 371 mm. Note that the radius is dynamic rolling which allows for tyre deformation due to the vehicle weight so doubling the result is 5-10mm less than the nominal tyre diameter.

[allisong]

Thanks for the reply! The tyre circumference in the RRS is in the EUCD section of the config, in my case 2320mm.

I find that the MSB and LSB figure alters the speedo and odometer. If I change mine from 106 to 116 the odometer now suits the larger FFRR tyres and the speedo goes back to being optimistic from being spot on. This can be corrected by setting the region to 0% a already documented above!

What fun, we are slowly getting there.

[Graeme]

I hadn't detected the relationhip between the rolling radius and the speedo but my fiddling wasn't exhaustive, being content with achieving the correct speeds and distance. Its also possible that ecu logic has changed parameter usage since I played with the parameters.

Perhaps BBS have updated their software with more fields displayed since I saved my original data which does not show the circumference in the EUCD section. It might be time to save another copy, having recently updated to the latest VE version.

[flotty1974]

The only way to check an accurate speed out of your car is to stick it on a certified set of rollers. When I say certified, I mean from those measures and standards people (I think the automotive societies/associations have them and hopefully your LR mechanic). GPS is unreliable and as such is not used in court (sorry for all those wanting to challenge speeding tickets off of GPS)there have been a number of cases around the country that have proven this (unless the lawyers in the crowd wish to challenge or support this). Obviously with tyre wear it varies the outcome and GPS is very very close but not classed as accurate. To answer the original question, no it isn't something to worry about, go off of your speedo and not the GPS and make sure your dealer calibrates it when you go in for a service.

[allisong]

I have now carried out some extensive work on my RRS 2010 TDV8 with MSV2 Faultmate and CCF and EUCD config files. The situation I have is that my RRS was delivered with 275/40 R20 tyres/wheels and I run FFRR rims and tyres on the vehicle and these are 255/50 R20. The increased “rolling” distance of the larger tyres is about 3.34%. As the speedo was already set to read faster than the actual speed, it became fairly“accurate” without any change of settings, (read 71 mph when actually doing 70mph and this is reflected across all speeds). However the ODOmeter became 6.13% inaccurate (for 106.13 miles travelled it reads 100 miles). This is already strange as it should have been about 3.34% wrong, but as I do not have the original wheels and tyres I cannot confirm what it read before the change, but it seems likely it was always somewhat wrong! This also influences the fuel consumption figure and this is set to 7% in the CCF, (I have not tested the influence of this setting yet).

So back to the CCF and EUCD settings. There are many entries that “could” potentially influence the speedo and odometer readings, but many of them do not influence these at all, and some are used for other modules.

This is what I found from changing the settings and testing:

CCF Settings “Wheels / Tyres and Brakes” Section:

Tyre Dynamic Rolling Radius MSB: 1
Tyre Dynamic Rolling Radius LSB: 115 (was 103)

This setting does not influence the speedo or ODOmeter at all! It does set the ABS and Adaptive Cruise Control (ACC) to use the correct wheel speeds, however, and it is VITAL that this is set correctly. If not set correctly the ACC will more often error with “radar signal blocked” and “forward alert disabled”. It is harder to assess the impact on the ABS, but if a silly figure is used the ABS will not function. The setting is calculated by MSB: 1 x 256 + LSB: 103 = 259 mm (revised in my case to 1 x 256 + 115 = 371 mm – the new rolling radius). Please note that this is the “Dynamic Rolling Radius” and can be calculated from the actual tyre data, in my case the tyres actually turn 691 revolutions per mile(varied from 691 to 693 between Continental, Pirelli and Michelin data). They also have a dynamic rolling length of 2330mm. All this data fortunately adds up but is quite hard to find from the manufacturers. Fortunately I also have a FFRR and could also compare the CCF & EUCD settings between vehicles also!

Wheel Rim Width: 8.5 inch (was 9.5 inch)
Wheel Rim Diameter: 20 inch
Tyre Width: 255mm (was 275mm)
Tyre Aspect Ratio: 50% (was 40%)

These settings have no influence on any system that I could measure. They seem to just be used for information only. They are not set at all in the FFRR (set as "undefined)".

CCF Settings “Warnings and Messages” Section:

Speedometer Offset: 167

I have not tested whether this setting has any influence. It is set to a different value in the FFRR (127)

CCF Settings “Miscellaneous and Unused” Section:

Jaguar Speedometer Calibration Market: Market0: 3.5% +2kph (option Market12% + 0kph)

This setting influences the speedo reading but not the ODOmeter reading. In my case the “Market0”setting was already set and actually results in a speedo that consistently reads 1 mph fast across all speeds. This is logical as the 3.5% is completely nullified as I have tyres that have a rolling distance increase of 3.34%, therefore, in effect, the only factor in play is the +2kph. I tried the “Market1”option and tested, the speedo then read a lower speed than the vehicle actual speed from 1 mph at 30mph to 2-3mph at 70mph and this is consistent with the setting and tyre size. I have confirmed this effect with the FFRR by using the “Market1”setting on that vehicle and now the speedo is accurate (it runs the standard tyres: 255/50 R20).

Jaguar KPH Offset: +2.0kph (a range of settings can be used)
Jaguar Percentage Scaling Factor: 3.5% (a range of settings can be used)

As previously reported by Graeme, these settings influence the cruise control setting and if they do not match the market value above then when you set the cruise control to 70, you may actually see that you are doing a different speed according to the speedo reading, very strange. So the simple advice is to always set these to the same value as the market value.

EUCD Settings “EUCD Wheels / Tyres and Brakes” Section:

Tyre Circumference: Rolling circumference 2330mm (was 2220mm)
Tyre Dimension: 255/50 R20 AT (was 275/40 R20 AT)

The Tyre Circumference setting was set to 2220 mm for the 275/40 R20 tyres. It is set to 2330 mm in the FFRR and this calculates correctly from the rolling radius so I now use this figure in the RRS. The Tyre Dimension setting reflects the tyres fitted in both the RRS and FFRR. However I cannot see any influence on any instrument or modules from the change to these settings, so they seem to be forinformation only.

So that concludes my findings, testing these settings is time consuming, as to do this you have to change a single setting and test each one on the road! So far I have not found anything that will influence the ODOmeter reading and I now think that is encoded into the VBF file (firmware) loaded into the instrument cluster for each vehicle, I will take a look at the firmware for the D4 versus the RRS as they use the same instrument pack!

Hope this helps for anyone thinking of changing these settings.

[allisong]

Apologies, there is a mathmatical error in the above post! It should have read:

CCF Settings “Wheels / Tyres and Brakes” Section:

Tyre Dynamic Rolling Radius MSB: 1
Tyre Dynamic Rolling Radius LSB: 115 (was 103)

This setting does not influence the speedo or ODOmeter at all! It does set the ABS and Adaptive Cruise Control (ACC) to use the correct wheel speeds, however, and it is VITAL that this is set correctly. If not set correctly the ACC will more often error with “radar signal blocked” and “forward alert disabled”. It is harder to assess the impact on the ABS, but if a silly figure is used the ABS will not function. The setting is calculated by MSB: 1 x 256 + LSB: 103 = 359 mm revised in my case to 1 x 256 + 115 = 371 mm – the new rolling radius).

[Glynhouse]

Nearly 3 pages so far, does it really matter ?
Of interest - yes.

For what it is worth the MY07 I picked up exactly 12 months ago, on the way back from Brisbane to Cairns read just under 2kph (roughly bit hard to tell) fast compared to the Garmin. I have 2 GPS's both read around the same. Vehicle had new tyres on standard 18" wheels, original tyres fitted new to match when I bought it. (G/Y Wranglers)
Cruiser I sold was about spot on with new Grandtreks on it original fitments, when I went to Pirelli ATR's it read 5kph fast, and considerably more when they were worn.
Both vehicles with new tyres measure about spot on with the 5klm test strips on the highways.

DD

[NavyDiver]

That is about what it should be.

Garry
Why Gary. 10% should be rubbish car not top of the pops D4. 5km out is not in my opinion very good. My GPS is almost perfect. 17 inch with mud tires on my D3 are as well on the speedo. 18inch ATs are out by about 5km at 100kph. I know we can alter this with gizmos but is it to much to ask for an acurate speed reading? I took toyota to task over a car (Lexus) which was fixed. Landrover can fix it. Why wont they fix it when they can?

[TerryO]

I suggest weakestlink it you want to debate with Garry a comment he made nearly three years ago then you let him know that you have responded.


cheers,
Terry:)