Just spoke two techs about this yesterday.
A wider tire on stock rim decreases the tires contact patch with the road.
Rider probably will not notice the slight difference....until pressing very hard in a corner.
Think what happens to the contact area when you pinch the tire rims together.
See what happens?:-)
Now a wider wheel rim is a whole 'nather story!!!
,A wider tire on a wider rim increases the contact with the road.....but can offer up ither issues on that bike.
Made sense to me.
Stig