Update:
Since my above posts, I finally had time to change tire (rubber) size. Below is something I posted on a different thread. Outcome: Very happy I upgraded to smaller diameter size tire - with larger load weight ratings as well. Especially for my hauling & towing needs.
Yes. Speedo is slight off (with the 1.45% smaller size rubber). Dash Gauge speed shows 65 MPH (as per engine RPMs). Dash GPS ground speed in reality shows 63 MPH. Variance is not worth worrying about - especially since we tend to drive slightly above speed limit anyway. Best part of all, it's new slightly higher engine RPM creates transmission's less "lugging" and less down shifting on the hills - which sucks life expectancy out of the transmission...
For my 2017 DGC SXT that I use for long haul and cargo towing / trailering, it uses factory 17" black steel 6.5" side rims, factory 17" chrome / plastic hub caps and 235/60R17 Yokohama AVID ASCEND 103H (which are XL rated) rubber. Yes. 1.45% smaller size than factory rubber 225/65/17 size. NO pics but visually, one cannot see a difference (on the outside).... 235/60R17 is better than factory for my usage....