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We use our catalogue of structural decomposition measurements for theextended GALEX Arecibo SDSS Survey (xGASS) to study the role of bulges bothalong and across the galaxy star-forming main sequence (SFMS). We show that theslope in the $sSFR$-$M_{\star}$ relation flattens by $\sim$0.1 dex per decadein $M_{\star}$ when re-normalising $sSFR$ by disc stellar mass instead of totalstellar mass. However, recasting the $sSFR$-$M_{\star}$ relation into theframework of only disc-specific quantities shows that a residual trend remainsagainst disc stellar mass with equivalent slope and comparable scatter to thatof the total galaxy relation. This suggests that the residual declining slopeof the SFMS is intrinsic to the disc components of galaxies. We furtherinvestigate the distribution of bulge-to-total ratios ($B/T$) as a function ofdistance from the SFMS ($\Delta SFR_{MS}$). At all stellar masses, the average$B/T$ of local galaxies decreases monotonically with increasing $\DeltaSFR_{MS}$. Contrary to previous works, we find that the upper-envelope of theSFMS is not dominated by objects with a significant bulge component. This rulesout a scenario in which, in the local Universe, objects with increased starformation activity are simultaneously experiencing a significant bulge growth.We suggest that much of the discrepancies between different works studying therole of bulges originates from differences in the methodology of structurallydecomposing galaxies.

xGASS: The Role of Bulges Along and Across the Local Star-Forming Main Sequence