I made a wheel rolling. The animation show a bet slow speed when start and end it. How to fix this. here is my file [http://www.filedropper.com/wheel]
I believe your referring to the curve on the animation of an object. When you set keyframes or keys in Blender, it makes a graph of how the property you keyed changes over time. By default, the curve has bezier easing, so it tries to animate more smoothly. This results in your wheel slowly starting to spin and slowing down before it stops.
You can change how the animation behaves by editing your keyframes as curves in the graph editor window. You probably want to make your curve linear.
SteveW gives a good explanation of linear interpolation for Blender animations in this question: