The phrase "flat underside" means the bottom part or surface of something that is completely level and without any curves or bumps.
Sentences with «flat underside»
A new, almost completely flat underside aids airflow under the vehicle and combines with a rear diffuser to optimise downforce — effectively «sucking» the car onto the road. (ausmotive.com)
Universal cast Alloy wing support mounts (satin black powder coated) with flat underside for boot or roof mounting (supplied each). (reverie.ltd.uk)
Optimized aerodynamics are achieved by the Type R's extreme body kit, consisting of a wide front splitter, deep side skirts, an almost completely flat underside, and downforce - optimizing rear diffuser and spoiler. (autofocus.ca)