This upgrade does not influence driving features. It is only about the appearance. Each truck offers different options as each make has different parts.
The chassis is a crucial element which controls the stability and turning. The chassis in 4x2 version (the rear axle has four wheels) turns well but does not provide too much grip. This parameter is much better in 6x2 version (two rear axles with respectively two and four wheels). The best grip is offered by the 6x4 version (two rear axles with four wheels each).
Available engines depend on a selected truck make. However, the power is the king! The more HP the better. Pay attention to torque as well. It is expressed in Nm - the bigger the better. The last parameters are revolutions (expressed in rpm) - the higher the better.
The gearbox depends on the engine you have chosen. The more expensive, the better. A better gearbox reacts quicker to gear change. If there is an "R" letter near a gear it means it has a retarder.
Each vehicle looks different inside. However, each is available in two versions: a standard one and exclusive (both in continental and British version) one. It does not influence the driving parameters, only aesthetics and available GPS.
The truck customization tool offers only colors and patterns created for that model by its producer. Therefore the choice is not very spectacular.
Two last tabs are accessories. The first gives you access to those assembled outside and the other one to those assembled in a cabin.
The choice is wide: chromium plated covers, exhaust system pipes, mirrors, wheels, additional lighting, driver's plates, steps and even handles. Each circle gives you access to other upgrades.
Some of items available in this category are the same as those in the cabin category.
Here you are not limited to colors offered by the manufacturer. The higher level the more patterns you unlock and each can be changed to make your truck really unique. You can select patterns available from DLCs as well.