Foosang, W. Gamelin, A. Nagaoka, R. JACoW Publishing Geneva, Switzerland 2673-5490 978-3-95450-227-1 10.18429/JACoW-IPAC2022-WEPOMS001 English 2225-2228 Contribution to a conference proceedings 2022 2022-07 https://doi.org/10.18429/JACoW-IPAC2022-WEPOMS001 https://jacow.org/ipac2022/papers/wepoms001.pdf In the context of SOLEIL Upgrade, the 4th generation storage ring project of SOLEIL, several methods are pursued to extend the beam lifetime and limit the emittance growth by reducing the Touschek effect and intra-beam scattering. Betatron coupling is one of the potential techniques to achieve this objective as it can increase the beam volume by transforming a flat beam into a round beam. However, the effect of the coupling on the collective effects is not fully comprehended, but some studies have shown an improvement in transverse instability thresholds. It was, therefore, crucial to investigate the impact of coupling on beam instability for SOLEIL Upgrade. This work presents numerical studies on the impact of coupling on the transverse mode-coupling and the head-tail instabilities. The results showed that coupling could be not only beneficial, but also detrimental.