We study the spreading of characteristics for a class of one-dimensional sc
alar conservation laws for which the flux function has one point of inflect
ion. It is well known that in the convex case the characteristic speed sati
sfies a one-sided Lipschitz estimate. Using Dafermos' theory of generalized
characteristics, we show that the characteristic speed in the non-convex c
ase satisfies an Holder estimate. In addition, we give a one-sided Lipschit
z estimate with an error term given by the decrease of the total variation
of the solution.