Originally Posted by Strongjeff
Because technically it is wrong. It can cause uneven wear patterns. When the sidewall is bowed to fit a narrower rim, it starts to pull the outside tread blocks down. This can cause the tire to wear in the center a little more then normal.
In extreme conditions I would say you're correct but when speaking about 10mm outside of the norm id say that's not necessarily true.
You also have to factor in the actual width of the tire being used.
As you know a 295 width wheel is not the same with every manufacturer.
Years ago I drove a 4th gen fbody and all the stock SS, WS6, Firehawks had 17x9 inch wheels with 275/40/17's.
295 is 20mm or .787 inches wider than a 275 and obviously a 9" rim is 1 inch wider so it's a better fit.
As long as you proper inflate you won't have an issue.