"To tune the car" means making adjustments or modifications to improve its performance, such as enhancing the engine, suspension, or other components to enhance speed, power, handling, or overall efficiency. Full definition
This tuning is very cool and also special for me because it makes part from that category with tuned cars in a mode very pleasant to me. (automotorblog.com)
However, don't expect to be able to fine tune a car... that is still the bread and butter of the simulation games. (thelatenightsession.com)
In fact, it is entirely possible to complete the career mode up to class S with less than 5 finely tuned cars. (newgamenetwork.com)