l'm always facing this problem when it's came to the curve modifier in creating the wheels ..... an extra curved face ..... like this below 
Hi Ahmed,
Could it be that you have some Scale issues?
I assume you have your Array set to "Fit Curve".
Make sure to Apply the Scale of your Mesh.
If you have Scaled your Curve in Object Mode, you should ALT+S, to Reset the Scale of the Curve and then Scale it back again in Edit Mode.
But you don't have a Curve Modifier on the tires, did you Apply that already? In that case, you should go back in time a bit, to before Applying the Curve Modifier.
