About the automatic merging issue in array modifiers. ( About "Tread" )

 Hi 凯 胡 CCash_Hoo ,

That is perfectly normal with this method. You'll just have to adjust the (in your case) Z-scale of the single rubber segment until it fits the circle (and Merges the first and last sides).

An alternative method, that avoids this merging problem (but which only works if the two sides of the segment are straight and parallel, which they seem to be in your case) is, to use a Simple Deform Modifier, that is set to Bend 360° (often, the Empty, used as Origin point for the bending, needs to be rotated 90° around one of the main Axes). So a Modifier stack like this:

Maybe also your merge setting is the array modifier is set to off? Because they don't seem to merge, the difference in shading is a sign of that?

Hey Omar, the O.P. has Merge enabled, as you can see:

But there is a Curve Modifier after that and that doesn't do another Merge (therefor a Weld Modifier after the Curve Modifier, bu t before the Subsurf, might help...)

Dangs you can read that, Phil is right you should right a book. I think the only mystery here is why there is a shading difference if it is merging. For sure the weld might help.