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We present a new dispersive framework for the extraction of the strongcoupling constant $\alpha_s$ from $\tau$-lepton decays. A new feature of ourprocedure is the use of the quark-hadron duality on the limited region $s_{\rmd}<s<m_{\tau}^{2}$. The duality point $s_{\rm d}$ and the $\bar{\rm MS}$ strongcoupling constant $\alpha_{s}(m_{\tau}^{2})$ are self-consistently extractedfrom the $\tau$ data for the non-strange vector spectral function. We use 2005ALEPH and 1998 OPAL experimental data on the vector spectral function. Wecompare the new framework with the contour improved perturbation theory up toorder $\alpha_s^{5}$. The new procedure yields systematically lower values for$\alpha_s$. From the 2005 ALEPH data, we obtain$\alpha_{s}(m_{\tau}^{2})=0.308\pm 0.014_{\rm exp}\pm 0.005_{\rm th}$ whichcorresponds to $\alpha_{s}(M_{\rm_{z}}^{2})=0.1170\pm 0.0018_{\rm exp}\pm0.0007_{\rm th}\pm 0.0005_{\rm ev}$. The extracted value for the duality point$s_{\rm d}$ is found surprisingly stable against perturbation theorycorrections $s_{\rm d}= 1.71\pm 0.05_{\rm exp}\pm 0.00_{\rm th}\,\, {\rmGeV^{2}}$. From the 1998 OPAL data, we obtain$\alpha_{s}(m_{\tau}^{2})=0.290\pm 0.023_{\rm exp}$ and $s_{\rm d}=1.68\pm0.10_{\rm exp}\,\, {\rm GeV^{2}}$.

Strong Coupling Constant from $\tau$ Decay within a Dispersive Approach to Perturbative QCD