Thread: D4 Speedo v GPS

Originally Posted by 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....

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

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

That is about what it should be.

Garry

Originally Posted by 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

what it should be!

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.

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.

Originally Posted by garrycol

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 !!!

Regards,

Les.

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.