Col, let us know if you have any success in adjusting your speedo through the CCF changes. I've changed the tyre size and circumference values in the CCF a few times and I don't think it's made any difference. Kev

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Kev, played about with them before as well and didn't think It made a blind bit of difference either, but never really changed the rolling circumference by any significant amount though. The list of different circumference in the CCF only goes up to 2385mm which is pretty close to my required calculated figure of 2405mm although quite a bit more than the original factory set one of 2220mm for the 275/40x20 wheel, but will try it to see if there is any real change. Not to bothered as the speedo reading with nothing changed except the actual wheel/tyre size the speedo is reading spot on when compared to the road side display cameras, which there a quite a lot of here, the digital readout on the speedo is exactly the same as the camera although not sure what the tolerance allowances are on the cameras. Haven't been brave enough to actualy try it through speed traps though to see what reading we get on the ticket. As far as the false fuel consumption figure is concerned I think most of the guy's that have the 5.0L S/C will agree that economy is not really the primary concern with them.

Cheers
Col

Just did a comparison, currently have 275/45 x 21" wheels and tyres fitted. CCF file set at original factory setting of 275/40 x 20" wheel/tyre with rolling circumference of 2220mm. 30mph on speedo digital readout, 30mph on GPS at 50mph on speedo read 51mph on GPS, 70mph on speedo read 72mph on GPS. Changed CCF file setting to 275/45 x 21" wheel/tyre with rolling circumference of 2385mm.

Got exactly same figures as before, so in my case changing the tyre/wheel size combinations didn't make a blind bit of difference to the speedo reading, might try playing about with just the rolling circumference to see if that changes anything sometime, but happy with speedo accuracy as is. The only thing I did notice is set cruise at 70mph digital readout but the cruise setting message saying set speed was 68mph but was the same for both CCF file settings, but have a feeling it has always been like that but not sure.

Did exactly same route both times, only 6 miles admittedly but original CCF file setting trip readout returned 6 miles, average speed 15mph and 13.5 mpg, second setting 6 miles average speed 23mph and 16.5mpg so little puzzled with that one, will have to wait until do longer trip to see which is most accurate.

Cheers
Col

Must read page 2 first  2006 2.7 TDV6 HSE in Cairns Blue.