In most cases and I know the previous image may look funny and very basic, but I always get asked by people who want to model a high res realistic car and they still don't test with the basics and keep asking why their mesh looks like clay with no sharp edges at the right places, so please forgive me for this.
After you start adding edge loops and details, things sometimes start to turn the other way around; your mesh becomes messy with no decent flow and doesn't feel smooth, I take for example this part of a model I made at an early stage, I will try to demonstrate what I mean.
Now you could, in some cases avoid adding the edge loops all over by trying to do it smart to get the sharpness you want with as few edges as you can. Try to make an even distribution of edges to fix the areas which gets messed up as a result of adding edges, even if it means adding even more edges, but please try to understand how mesh smooth works when you add edges and anticipate what effect they will have.
By the way if anyone found any difficulties doing this mesh, you he can check wire frames of finished cars and try to learn from them or you can use your tablet to draw a basic wireframe on any image similar to the image below. If you don't have a tablet, just print the image out and draw on it using your pencil, this image will help you realise how to start modelling it. As you can see from my rough drawing, anything will do. I don't draw the wireframe now but when I was starting out learning about edge loops it helped me, you can do as I do now, just look at the model and visualize how you are going to do the edge loops and it will make your modelling faster.
Car Rendering Tutorial
This tutorial will be about rendering a car in 2 different styles. I used VRay to render, but you can do the same in all renders, it's the same principle.
Firstly, I would like to thank Dominick Cliff, Who made a very short tutorial way back about rendering a car, but it helped me to understand the importance of the surrounding environment for reflections. The cool thing about HDRI is that it makes life a lot easier, it stores both light information and the environment to reflect as well, which makes sense. The most crucial thing to take care about when using an HDRI is that it should fit with the background image or scene you are using if it wasn't taken from the HDRI it self.
For example, you obviously can't just put a car on a white background with an HDRI reflecting a beach, it will look apparent even if the reflections on the car and all the render settings and materials are perfect.
In some cases when the HDRI is similar to your scene, but not enough, you can try to put the HDRI in a mix map to try to add a different tone of colour to it and play with the light value of the HDRI to make it as close as possible to your scene, but in studio style or other types of renders or scenes with no similar HDRI maps or closed sets etc, it becomes hard to use an HDRI which will give you what you want. There are ready HDRI's in white and black colour which are prepared to simulate lights in a studio, but they can't always give you the results you're after. That's why for studio renders I always depend mainly on lights or reflection from the objects that I make.
I will start off with the material so you can test the lights on a good material.
Now the material or shader key to any successful car paint should be multilayer. In order to make car paint more realistic, it's not enough to put in just one layer with fresnel reflections. When you observe car paint in real life, and especially when there is intense sun on it you see it reflecting the sunlight but you can also see the sun being reflected in a glossy blurred reflection. This is why we need to make the 3d car paint in more than one layer.
For people using Brazil renderer or mental ray in Maya, you have a ready car paint material/ shader to use. These will include multilayer reflection and more details by default, it will be easier to use the car paint materials there.
Anyway as you can see in the image the reflection will come in different layers.
Just put a base material with it to make the most of the material and a subtle, but needed, other material or 2 to simulate the blurry reflections layer. For this I used a shellac material, the first main slot is a simple fresnel reflecting material, the second slot is actually a blend material containing a blurry reflections material and a very blurry material (so its actually 3 materials altogether but you get the idea). By blurry I mean 'less glossy' material (a value of 1 glossiness will make a shiny surface, a value of 0 will generate an extremely blurry surface).
You could generate glossy surfaces by using a bump map (tiny bumps on the surface of the objects make them glossy in the first place, so the shape of the bumps will determine how the surface is blurred) but it's faster and easier to just play with glossiness parameter.
Here are the material settings:
One thing to mention is that my material is not coloured since its black, obviously, but just by changing the diffuse colour of the main material you will be able to have any colour you want. You can try putting different colours in the less glossy materials as well for different effects.
The other thing is that I didn't simulate the sparkling effect of metallic car paint flecks. The reason is that, after observing and checking reference images, I noticed that unless you are doing a very high res extreme close-up image for a car reflecting an HDRI or scene, you can do without it, by adding another layer for: A little trick I used was to not increase the subdiv's of the reflective glossiness to give the surface just a bit of a grainy look. Here are car paint flecks in action, don't forget that car paints come in different variations; some have flip paint (cool paint which changes colour depending on your viewing angle) and many more, but if you can understand how it works you can simply apply it all using blend, shellac materials and different falloff maps.
The image below is of a car Mirror flicker (you can imagine how much close-up it is.