Create a new document with settings for example 3000 pixels wide X 2300 pixels high. From the tool palette, select the Brush Tool (B), and then select the icon: "Pressure", thanks to that the pen tablet will respond to your pressure so as to obtain a smooth line brush. In the settings, choose size "3" tip hard. In the tab "Layers": double-click on the first layer (Background). Draw a sketch of your concept car.
Continue sketching. Think and design pattern of the wheels. To facilitate the work, you can draw a pattern on one wheel first, then copy and move them to the rear. When the sketch is finished, removed completely unnecessary lines (eg, those that go beyond the "body" of the vehicle}.
From the color palette, choose a slightly darker shade of the same color as before, (in this case it's: #E0C822). Choose a soft brush and set the size to 100, opacity 15%. Create a new layer. Apply the color to the "body" of the car. Remove unnecessary brush strokes.
Create a new layer. Choose black color from the color palette. Select a tool "Ellipse". From the options bar, select "Shape" and while holding the SHIFT key, draw a circle. Using the Shape option, the path of the wheels will be created automatically, which can be used in the later stages.
Create a new layer. Choose black color #000000. Set the brush size of 3-5 and opacity of 100%. Draw the rim cavity, as in the picture. To make it easier for you, the wheels can create a selection. So you do not go beyond the selection brush.
Create a group of layers. Move all the layers containing the elements of the front wheel to this group. Copy group and while holding down Shift key, drag a copy to the rear so you will have second wheel in the back. Create bottom black shadow under the car using black color #000000.
Create a new layer. From the color palette, select lighter color than the color of the current window (in this case, it is a gray color). Select the Pen tool (P) and shape into a path that will mimic the glass on the other side of the car. In the "Path" tab, click on the button "Fill Path color". Add more details on the side.
Now add the first shades to the car body. For this purpose is necessary to create a new layer. Move it under layers with the wheels but before the layer contains main color of the car body. From the color palette, choose a slightly darker color (it is a: #DABD01). To impose this color I used the brush: "Square (coal)"