  Quark model results for the $B\to \pi,\rho$ decays are analysed, making use
of the dispersion formulation of the model: The form factors at $q^2>0$ are
expressed as relativistic invariant double spectral representation over
invariant masses of the initial and final mesons through their light--cone wave
functions. The dependence of the results on the quark model parameters is
studied. For various versions of the quark model the ranges $\Gamma(\bar
B^0\to\pi^+e\bar\nu)=(7\pm2)\times10^{12}|V_{ub}|^2\; s^{-1}$, $\Gamma(\bar
B^0\to\rho^+e\bar\nu)/\Gamma(\bar B^0\to\pi^+e\bar\nu)=1.45\pm0.1$, and
$\Gamma_L/\Gamma_T=0.7\pm0.08$ are found. The effects of the constituent quark
transition form factor are briefly discussed.
