For this reason ceramic and porcelain tile floors can be considered somewhat delicate despite the inherent strength of the material.
Subfloor material for ceramic tile.
Concrete expands and contracts and that type of movement can also crack the tiles and the grout.
Materials such as vinyl and carpeting are flexible enough to tolerate engineered floor truss systems with larger joist spacings such as 24 inches on center.
Underlayment is the material placed on top of the subfloor that assists in the installation of the tile or other type of flooring.
Tile floors are heavy and tile is a hard material.
It will break or dislodge if the surface bends under the load.
Cement backer board can provide a solid flat surface to install tiles on if you have a wood subfloor.
It sounds like your joists are well within the acceptable limits of l 300 so your main concern is the deflection of the subfloor between joists.
When installing a ceramic tile floor on a concrete subfloor you don t have to worry about flexing as long as the concrete slab is at least 1 1 8 inch thick which most slabs are.
A plywood subfloor must be structurally sound and able to support the installation.
With ceramic tile you also need to limit the deflection between joists which is a function of the subfloor thickness and how it is installed.
However you re not out of the woods.
Check for dips in the floor by sliding a 4 foot to 6 foot straight edge in different directions all around the room.
For ceramic tile the tile council recommends using joists that are 16 inches on center a 3 4 inch thick plywood subfloor and a 1 2 inch thick cement backer board or concrete slab.