Joy of joys. Just found out that there is a setting in the IID Tool Car Configuration File menu to allow users to specify the tire size currently fitted to the car. This means that those people who are running larger diameter tires can have their speedometer reading the proper speed again.

Is it a big deal? Maybe not, but that 2-3mph difference bugs me all the time!

 

What menu is it under?

 

Update your IID.
It's under the instrument panel config menu

 

its also spelled tyres in there lol

 

BTW, just in case anybody does this, I'd like to know what your results are. I updated mine to the current tire size and not long after, I got a check engine light. Turns out it was for the "vehicle speed sensor". Cleared the code and it came back. Returned tire size to default and haven't had the check engine light come on again.

Obviously, there appears to be more to it than just updating the tire size in the CCF

 

I’ve done the same car configure update for my larger 275/65/R18 tires. Got the same trouble code. So far I’ve gotten it to work without a code when set to 390mm (should be 408mm). Not sure if there is something else I need to change to get the right tire radius setting without a trouble code.

anyone else have a better experience or guidance?

 

Mine i think is set to 401mm with 265/65/18 and still reads over by about 4kph which is a good safety margin.

 

It is a train wreck and a shame that GAP has not devised some sorta internal calculator to make this easy. My speed reads over by 2mph, which is fine. But during really tight turns my ABS will get triggered. When I try other values, I get faults. The numbers seem to be sorta arbitrary. I think even entering that I have 18" versus 19" wheels cause a fault on its own. Not that wheel size matters at all, just actual tire diameter. I have not had time sit down and really dial it in. Also when I did research on this, I found that with my GAP tool I dont have some of the same settings available, so that does not help. Assuming software updates and changes in software?

 

I haven’t checked my speedometer vs GPS for accuracy yet - curious to discover any discrepancies.

While the Gap tool has been great, it does have its limitations - probably a combination of landrover software and gap software deficiencies. Something like changing tire size should be very straightforward. Not sure why landrover or gap wouldn’t allow for any theoretical tire size since it’s a basic equation for speed.

Do you base your tire radius on the nominal tire size or take a measurement from center of axel to ground to account for tire deformation under load?

 

When I changed my tires size on the 6G Bronco I owned, one had to do a PCM and TCM reset or you would get a DTC. Since there is a good amount of Ford DNA contaminating our LR3's I have to wonder if there might be something similar needed to sigificantly change tire size.

Just for reference, I found this - https://www.bronco6g.com/forum/threa...-bronco.23064/
This did work on the Bronco.
The other thing I found was the calculation for the correction one needed. I went through a whole series of calculations involving tire diamters and revolutions per mile and at the end found it was way off. Next I tried reading the speed off the speedo and GPS, divided to come up with a ratio, applied that to the correction and it was spot on.