The phrase "to tune the vehicle" means to make adjustments or modifications to the vehicle's engine and other parts in order to improve its performance and efficiency. Full definition
Fine tune your vehicles with a RPG - style upgrade system and compete in split - screen races for up to 4 - players or play online against opponents on other platforms. (nintendo-insider.com)
Things such as replacing parts after accidents, restoring classic vehicles, or fine - tuning vehicles for racing often require custom fabrication jobs. (yellowpages.com)
They could then use those credits to purchase upgrades to fine tune their vehicle. (ps3attitude.com)