The equid locomotor transition is one of the most iconic morphofunctional shifts in terrestrial mammals. Throughout their evolution, equids reduced their side-digits, with different phylogenetic clades exhibiting greater or lesser degrees of digit reduction. One hypothesised driver behind the reduction (and loss in equinin equids) of side-digits is their potential lack of functionality during locomotion. However, hipparionin equids retain side-digits until their extinction during the middle-Pleistocene, despite coexisting with monodactyl equids for over 7 Ma. In this study, we aim to shed light on the functionality of the side-digits of extinct equids using an extant morphological bracket, comparing toe-ground interception across ecologically diverse ungulates which exhibit side-digits. Modern and extinct ungulate proximal phalanges were measured and compared across a broad range of taxa using a toe-reduction index (a morphometric measure of central-to-side-toe length). Using high-resolution 3D scans, joint range-of-motion was estimated from osteological material; we then built and analysed a series of ungulate distal limb skeletons, rotating the third proximal phalange parasagittally at biologically realistic, regularly spaced intervals. Toe-to-ground interception for the side-digits was scored for the varying degrees of central digit extension, and under hypothetically increasing substrate compliances (mimicking different underfoot conditions, e.g. mud). Our results from toe-reduction indices align with 3D virtual ROM experiments, which themselves demonstrate widespread functionality in the side digits of transitional and hipparionin equids (e.g. Nannippus). This preliminary study refutes the notion of functional redundancy in equid side-digits, paving the way for more advanced investigations in the future.