Currently Being ModeratedFeb 6, 2014 5:38 PM (in response to 4thSpace)
I don't think you can change the width of a tab.
But note that you can quickly scroll through the tabs horizontally.
Move your cursor up to the band where all the tabs are and hold the mouse button down (or trackpad equivalent), and swipe left or right to quickly navigate to tabs out of view.
Currently Being ModeratedFeb 6, 2014 6:05 PM (in response to 4thSpace)
Ok. A lot of people (including me) first thought you had to scroll with the left and right triangles at the right of the band, which is slow. Moving the cursor into the band and swiping left and right is much better for me.
As far as I know there is no control to reduce the minimum width of the tabs, though the width will expand to accommodate long names.
If it's important to you maybe give Apple feedback at Numbers > Provide Numbers Feedback in your menu.