Q:

Modeling a car wheel arc: Move vertex to form an arc

I'm really noob with Blender and 3D modelling in general. I started modelling a *very* low polly car, and I wasn't careful at all about the topology, little by little I started adding some more detail to some parts, and end up trying to fix the topology also. I'm having the impression that maybe this is not so easy as to start with a good topology from the beginning. 
I'm currently trying to make the arc of the wheel resemble a semi-circle, right now is aproximated by eye.

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But till now I'm clueless about how to reorder those vertex so I can make the flow of the mesh start from the arc of the wheels to the rest of the body, this kind of flow:

Some more views of the car if needed: 
https://i.stack.imgur.com/ZwPqx.png
https://i.stack.imgur.com/RBIpe.png
https://i.stack.imgur.com/ypFV2.png

A:

There are two tools that can help you achieve that.
1) Scale to sphere (Alt + Shift + S)
2) LoopTools Addon to space out vertices.
I recommend you proceed like this:
Scale to sphere

Set the 3D cursor to the center of your arc. We will use it as the pivot point for scaling the vertices.
press "." (NOT on the NumPad) to set the pivot point to the 3D cursor
select all the vertices you want to sit on the arc.
press Alt + Shift + S and move your mouse until the vertices align on an arc.

Space the vertices

Enable the LoopTools Addon in the User Preferences
with the vertices selected, press W and select LoopTools - Space

