Given a spherical fibration ξ over the classifying space BG of a finite group G we define a dimension function for the m-fold fiber join of ξ, where m is some large positive integer. We show that the dimension functions satisfy the Borel-Smith conditions when m is large enough. As an application we prove that there exists no spherical fibration over the classifying space of (formula presented) with p- effective Euler class, generalizing a result of Ünlü (2004) about group actions on finite complexes homotopy equivalent to a sphere. We have been informed that this result will also appear in upcoming work of Alejandro Adem and Jesper Grodal as a corollary of a previously announced program on homotopy group actions due to Grodal.