Thread: D4 Speedo v GPS

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.

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