[TD5 Speedo Mileage run up circuit]

I think I got the algorithm and it is as an Excel formula:

=DEC2HEX(BITAND(255;1024+BITLSHIFT(BITAND(2*(BITAND(BITRSHIFT(A1;4);32771)+BITRSHIFT(A1;12));7)+5;4)-BITXOR(BITRSHIFT(A1;8);BITAND(A1;255)));2)

whereby the rate (in dec) is in the excel field "A1" (see also attached Excel file)

So the checksum for a rate of 2472 (=2548 - 3%) should be 0xEF ... maybe someone knowledgable could confirm this?

TD5SpeedometerAdjustmentChecksumCalc.xlsx

[TD5 Speedo Mileage run up circuit]

44 minutes ago, mickeyw said:

Is this in a 90 or 110?

I have 110 that has that size tyre. I find the is spot on according to 2 different GPS devices. Have you checked yours yet?

 I think normally a speedometer is intended to under read, so in my case a larger than standard tyre still achieves an accurate reading.

No, it's a 130 and I checked with a calibrated GPS and the speedometer shows slightly less than the GPS, which is illegal. So I have to do the adjustment 

[TD5 Speedo Mileage run up circuit]

Hi, 

I want to adjust my KPH to +3% to change the tires from 7.5R16 to 255/85R16 

So currently I should have a RATE=0x09F4 and Checksum:B3 

the +3% would mean I have to reduce the rate to d2472 or 0x09A8, correct?

I read through all of this thread, but in all honesty I don't get the algorithm you were talking about. So what would be the correct checksum for a rate of 0x9A8?

thx, Franz