The factory swinging arm on the Sixty-5 limits your choice of tyre, anything much above a 3.50", 410 or a 100/90 section is going to foul the chain guard or the front of the swinging arm. I tried an Avon 4.00" x 18" AM26 on one of mine, had it truly been 4" wide it would not have been a problem, but the width was actually 116mm or roughly 4⅝" inches. It might pay you to check the tyre data sheets in various manufacturers' web sites. With that tyre on, the wheel would only fit at the very back-end of the chain adjustment range.
A.