  We provide an explicit formula for all primary genus-zero $r$-spin
invariants. Our formula is piecewise polynomial in the monodromies at each
marked point and in $r$. To deduce the structure of these invariants, we use a
tropical realization of the corresponding cohomological field theories. We
observe that the collection of all WDVV relations is equivalent to the
relations deduced from the fact that genus-zero tropical CohFT cycles are
balanced.
