In the regions of the Tore Supra tokamak with significant ripple it is expected that a radial electric field (Er) ensures the ambipolarity of fluxes of thermal particles trapped in ripple wells. A neoclassical calculation (Connor and Hastie 1973 Nucl. Fusion13 221, Stringer 1972 Nucl. Fusion12 689) shows that Er is related to ion temperature and density gradients. The validity of this relation is investigated in a series of Tore Supra L-mode discharges without external momentum input. Doppler reflectometry measurements of fluctuations perpendicular velocity, which is dominated by the Er × B drift, are found to be in good agreement with the predicted neoclassical Er.