Details on car upgrades in NFS:Shift

The folks at gamerzines.com got a copy of Need for Speed SHIFT for a preview and decided to share the details with us in their blog.
Today we'll look at the "Upgrades" menu in Need for Speed SHIFT, which lets you improve the performance of every car in the game.
Levels I, II and III

Every car in SHIFT has access to numerous upgrades. As you progress through your career, more and more upgrade options for your car become available.
At this point, we can say that every car in the game has access to the same upgrades.
Each upgrade level lets you improve specific parts of your vehicle, including the transmission, engine, turbocharger, brakes, suspension and tires.
Naturally, each subsequent upgrade will cost more than the previous one. For example, upgrading the transmission to level one will cost $6,000, level two - $12,000 and level three - $15,000.
At the start of the game, only level-one upgrades will be available; the rest will gradually unlock once you reach a certain point in your career. Unfortunately, we can't say exactly at which points this happens, since we haven't figured it out ourselves:)
Upgrading your car isn't as clear-cut as it might seem. There are positive and negative sides. For example, while an engine upgrade has a positive effect on top speed and acceleration, the same change has a negative effect on your braking time. So you should always think before throwing money at the first upgrade you come across.
Aerodynamics

The fourth tab in the "Upgrades" menu lets you improve aerodynamics: choose an aerodynamic body kit option, change the interior and reduce the car's weight. There are also three levels here.
Interior upgrades are purely visual (aesthetic) changes - steering wheel, seats, additional gauges and material replacement.
Race Parts

The last tab in the menu is Race Parts. Here you can buy nitrous oxide, which gives you an extra boost during a race (level one provides 10 seconds, level two - 20), although replacing the exhaust system and tires will give a more substantial gain.
It's strange that when buying an upgrade that shortens the final gear, we got a more negative effect - speed and acceleration decreased, without any obvious positive changes. This may be a bug in the game in this preview version.
Source: gamerzines.com, nfsworld.ru