CamelToephy
Member
On my 2005 LR3 I recently swapped from OEM 255/55/19 to 275/65/18 and unsurprisingly the speedo is now off about 4-5mph at freeway speeds.
I have a Blackbox Rovacom-IQ, so I can reprogram the CCF. However, I'm having difficulties actually affecting the speedometer values with virtually any CCF edits.
NONE of these settings made any impact on the speedometer vs my GPS:
'Jaguar KPH Offset', 'Jaguar Percent Scaling Factor', 'Speedometer Offset', 'Jaguar Legacy Tyre Size LSB', 'Jaguar Legacy Tyre Size MSB', 'Tyre Aspect Ratio', 'Tyre Width', 'Wheel Rim Diameter'
The only value that affected the speedometer, was editing the 'Tyre Dynamic Rolling Radius LSB' value to 140. The problem is that changing this to any value other than the default of 114 triggers a check engine light with code P0610.
I know that later year model LR3s and LR4s can successfully edit this value, but maybe not the earlier LR3s?
I suspect I'll either have to choose between an inaccurate speedometer or the CEL but I wanted to check to make sure I'm not missing something here; including flashing an ECU with different firmware maybe?
-- Extra info on calculating the Rolling Radius for the lucky folks it won't trigger a CEL for --
The Dynamic Rolling Radius is calculated by first determining the radius of the tire size in mm.
This is 275mm * .65 = 178.75mm * 2 = 357.5 + (18 * 25.4) = 814.7 / 2 = 407.35mm static radius with slight variance from manufacturer to manufacturer.
Note the CCR value is the dynamic rolling (e.g. loaded weight) value, not the static value, which you can estimate by removing 2.8% from the static value.
Or just use the calculator at http://paws.kettering.edu/~amazzei/tire_calculator.html to work out the correct values.
Once you know the dynamic radius you calculate the MSB value by dividing by 256 and keeping only the whole number. The LSB is calculated by taking that whole number and subtracting the MSB * 256. Or more simply, since it's not likely anyone is putting 40" tires, the MSB will always be 1 and just subtract 256 to get the LSB.
For a 275/65/18 tire, the calculator gives the value 396mm as the dynamic rolling radius, so 396/256 = 1.546875, or MSB would be 1. The LSB is then calculated as 396 - (1* 256) = 140
I have a Blackbox Rovacom-IQ, so I can reprogram the CCF. However, I'm having difficulties actually affecting the speedometer values with virtually any CCF edits.
NONE of these settings made any impact on the speedometer vs my GPS:
'Jaguar KPH Offset', 'Jaguar Percent Scaling Factor', 'Speedometer Offset', 'Jaguar Legacy Tyre Size LSB', 'Jaguar Legacy Tyre Size MSB', 'Tyre Aspect Ratio', 'Tyre Width', 'Wheel Rim Diameter'
The only value that affected the speedometer, was editing the 'Tyre Dynamic Rolling Radius LSB' value to 140. The problem is that changing this to any value other than the default of 114 triggers a check engine light with code P0610.
I know that later year model LR3s and LR4s can successfully edit this value, but maybe not the earlier LR3s?
I suspect I'll either have to choose between an inaccurate speedometer or the CEL but I wanted to check to make sure I'm not missing something here; including flashing an ECU with different firmware maybe?
-- Extra info on calculating the Rolling Radius for the lucky folks it won't trigger a CEL for --
The Dynamic Rolling Radius is calculated by first determining the radius of the tire size in mm.
This is 275mm * .65 = 178.75mm * 2 = 357.5 + (18 * 25.4) = 814.7 / 2 = 407.35mm static radius with slight variance from manufacturer to manufacturer.
Note the CCR value is the dynamic rolling (e.g. loaded weight) value, not the static value, which you can estimate by removing 2.8% from the static value.
Or just use the calculator at http://paws.kettering.edu/~amazzei/tire_calculator.html to work out the correct values.
Once you know the dynamic radius you calculate the MSB value by dividing by 256 and keeping only the whole number. The LSB is calculated by taking that whole number and subtracting the MSB * 256. Or more simply, since it's not likely anyone is putting 40" tires, the MSB will always be 1 and just subtract 256 to get the LSB.
For a 275/65/18 tire, the calculator gives the value 396mm as the dynamic rolling radius, so 396/256 = 1.546875, or MSB would be 1. The LSB is then calculated as 396 - (1* 256) = 140
