Scheme variations of the QCD coupling and tau decays

The QCD coupling, αs, is not a physical observable since it depends on conventions related to the renormalization procedure. Here we discuss a redefinition of the coupling where changes of scheme are parametrised by a single parameter C. The new coupling is denoted αˆs and its running is scheme independent. Moreover, scheme variations become completely analogous to renormalization scale variations. We discuss how the coupling αˆs can be used in order to optimize predictions for the inclusive hadronic decays of the tau lepton. Preliminary investigations of the C-scheme in the presence of higher-order terms of the perturbative series are discussed here for the first time.