"To refine the handling" means to make improvements and adjustments to the way something is controlled or managed, usually with the goal of making it smoother, more efficient, or more effective. Full definition
Fans are rewarded this year with improvements in cabin quality, refined handling characteristics, and even styling updates. (autobytel.com)
The changes aren't huge, but they're refined the handling model so that it's the best yet. (wolfsgamingblog.com)
Weight distribution is balanced at 45:55 front to back, while several young engineers were tasked with refining the handling characteristics through multiple virtual on - track test sessions. (topspeed.com)