Apologies accepted and your explanation makes lots of sense on "stock" setup.

 

Okay, so with the greatest of respect, what have you (or anyone else) done to change to a 'non-stock" set-up? If you've increased the tyre profile size (and I can't think why anyone would want to do that), then yes the speed shown by the speedometer will be incorrect, but not due to a speed offset being applied to the speedometer in the DIM.

If I understand your side of the argument correctly, then you're saying that VH-platform cars in the United States of America have a speedometer offset applied to them at the factory, from new. Just for clarification, is that correct? That's what you believe? From the work that I have done on these cars over the years, particularly in terms of diagnostics and software, and the relevant information and documentation the I have been privy to, that's not what I understand to be the case.

 

Well that is my believe as they always show a higher speed on the speedo then actual GPS speed but I never worked for AM. Also by changing the size of the tires it will affect the speed sensors as you mention above, you can see the setup on my car at the moment which shows a different diameter and circumference. I don't know about the United States but I believe the cars are identical as they are sold back and forth across our borders, the only difference one can noticed is the Speedo in MPH vs KPH for Canada. I try to get some 265/35R19 for the front but they weren't available... the website I use for the tire calculation is https://www.willtheyfit.com

Just so you know I am not trying to argue as you have the knowledge from working on the car from the factory, I am just showing what I am seeing in my car by changing the tires from factory size to my new setup. We are so lucky to have people like you with all the knowledge from factory on these cars to help us and I am very grateful

 

No, the speed sensors remain the same, in terms of the distance travelled by the toothed tone wheel. It's the the rolling circumference of the wheel that changes.
Don't worry Handyman, I'm not trying to argue either. I'm just trying to explain why American VH-platform cars don't have the speedometer offset and how that potential offset works.