Hi Folks...

My local tire expert is strongly warning me against up-sizing my tires; saying that it will degrade the ABS functionality.

Have any of you who have already done so, noticed any change in ABS response or any impact on Crawl, Hill Start, Down Hill Assist...etc?

I would be surprised if it did cause a problem with ABS. ABS pretty much only cares about the difference in speed between the wheels while you are braking. Basically, if it detects the wheels spinning at different speeds while you are braking, it assumes there is slippage happening. Of course, there could be more complex things happening with the ABS system that I'm not aware of, but it's usually all based on detecting some wheels spinning at different speeds than others. I can't imagine how smaller or larger tires would cause problems with that. Maybe someone with a more nuanced understanding of the modern Toyota ABS could fill in the blanks?

I'd be very curious to hear your local tire person's explanation...

Check out these opinions: How do bigger tires affect VSC, TRAC, ABS