The rates of solvolysis of secondary p-toluenesulfonates in acetic acid or 97% trifluoroethanol are interpreted in terms of strain changes between substrate and the corresponding ketone. Such strain changes are obtained from force-field calculations (ΔE_st) and from equilibration of alcohols and ketones (ΔG_ox). This simple model reproduces the behaviour of substrates reacting by kc-pathways to afford unstrained carbenium ions. Anchimeric assistance and leaving group hindrance in the transition state are recognized in clear-cut cases by deviations from the expected reactivity. However, the model breaks down when highly strained carbenium ions of the cyclobutyl or 7-norbornyl type are involved.