Kubica to join Renault from BMW Sauber

POLISH racer Robert Kubica has vowed to mount a strong challenge for next season&rsquo;s world championship after signing for Renault.<br /><br />The 24-year-old, who came third when Britain&rsquo;s Lewis Hamilton won the 2008 title, is moving as his current team BMW Sauber are withdrawing from the sport.<br /><br />Renault have not won a championship since 2006, when Fernando Alonso secured the second of his back-to-back triumphs.<br /><br />But Kubica said: &ldquo;I&rsquo;m highly motivated and optimistic that together we can be at the front of the grid next year, and hopefully fighting for the world title.&rdquo;