The phrase "to flatten the bottom" means making something level or even, particularly referring to a surface that is not straight or smooth. Full definition
The AMG Line is offered as an alternative and features 18 inch light - alloy wheels, a diamond radiator grille, special bumpers and sills, upholstery in Artico mand made leather / Dynamic microfibre in black with contrasting topstiching, a multifunction sports steering wheel with flattened bottom section and AMG sport pedals. (mercedesblog.com)
Another highlight is the new generation of 3 - spoke steering wheels in different variants, including a multifunction sports steering wheel with flattened bottom section and red or black topstitching. (emercedesbenz.com)
The designers also flattened the bottom of the steering wheel with a straight segment of the rim. (automobilemag.com)