Adapt dimension axis of an object to viewport

i run into following problem: i try to make a wheel out of a cylinder. after creating the cylinder i rotate it 90° on x-axis. now i want to adapte the width of the wheel. unfortunately the object dimension axis is now not the same anymore like the viewport axis. when i reduce the width by changing the values in the dimension tab i have to change z instead of y (like it is in the viewport) to control the width. how can i change the dimension axis of the object (so that it aligns with the viewport again?).