Non-dimensional CME expansion rate evolution based on EUHFORIA simulations. Left column: derivation of the non-dimensional CME expansion rate ζ from the linear fitting of the CME speed profile in EUHFORIA simulations at D = 0.2 au (a), D = 1.0 au (b), and D = 1.8 au (c). Right column: non-dimensional CME expansion rate ζ_CME as a function of D (d), v_c, CME (e), and Δv_x, CME (f). Values observed at Wind are shown as blue diamonds. The green lines represent the fit for perturbed CMEs (dashed line), non-perturbed CME (thin continuous line) and for both sets of CMEs (thick continuous line) as reported by Gulisano et al. (2010).