The overcontact binary SS arietis

•New RV and light curve data.•Simultaneous roche modelling for this overcontact type-W binary.•M1 = 0.510 (15) m ʘ, m 2 = 1.521 (26) m ʘ, R1 = 0.87 (2) Rʘ, R2 = 1.42 (2) Rʘ.•L1 = 0.88 (8) l ʘ, and l 2 = 2.13 (21) l ʘ.•The more massive star is likely evolved, but the other, under-luminous.•The period change (OC) double sine relation of Kim et al. (2003) is no longer valid. A tentative 2-companion LiTE relation has been found. New radial velocity and photometric data for SS Ari have been obtained and analysed using the 2003 versions of the Wilson-Devinney code. Values for fundamental quantities have been obtained: M1 = 0.510 (15) M ʘ, M 2 = 1.521 (26) M ʘ, R1 = 0.87 (2) Rʘ, R2 = 1.42 (2) Rʘ, L1 = 0.88 (8) L ʘ, and L 2 = 2.13 (21) L ʘ. In addition to the values provided by the Wilson-Devinney output, luminosities have been computed directly using photometry from APASS, the Gaia distance, and estimates of the interstellar absorption. Although the two sets of luminosities compare well, the accuracy of the latter set is limited by the uncertainty in the APASS magnitudes. Although the TYC magnitudes for the comparison star are more precise, they produce higher luminosities (but still within error limits). In any case, the good agreement between the luminosities determined by the two methods suggests that they, and all other results in this paper, might be more reliable than previous values in the literature. Inserting the parameters into a Log(L)-Log(Teff) plot for each star using data from Yakut and Eggleton (2005) suggests that the more massive star is somewhat over-luminous and therefore evolved, whereas its companion is under-luminous. Analysis of the period behaviour with the aid of an eclipse timing difference (OC) plot reveals that the double sine relationship Kim et al. (2003) is no longer valid. A new LiTE relationship adding two companion stars has been obtained, but, in view of the fact the putative period of one of them is in the range of ∼600 years, the relationship must be regarded as very tentative indeed.