If you have an excessive number of tabs in your RadRibbonBar Tab Collection, you can use CSS to set the overflow to visible as follows:
In my test, I open a RadRibbonBar that has 3 tabs and add 14 new tabs, server-side on the Page_Load event. Adding the CSS allows me to show all tabs in two rows.
See the attached "radribbonbar_excesstabs.png" image for the resulting display.
Hope this helps!